/**
 * Copyright 2010 JogAmp Community. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are
 * permitted provided that the following conditions are met:
 *
 *    1. Redistributions of source code must retain the above copyright notice, this list of
 *       conditions and the following disclaimer.
 *
 *    2. Redistributions in binary form must reproduce the above copyright notice, this list
 *       of conditions and the following disclaimer in the documentation and/or other materials
 *       provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY JogAmp Community ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JogAmp Community OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * The views and conclusions contained in the software and documentation are those of the
 * authors and should not be interpreted as representing official policies, either expressed
 * or implied, of JogAmp Community.
 */

package com.jogamp.opengl.util.glsl;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.StringReader;
import java.net.URLConnection;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.IntBuffer;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Set;

import javax.media.opengl.GL;
import javax.media.opengl.GL2ES2;
import javax.media.opengl.GL3;
import javax.media.opengl.GL4;
import javax.media.opengl.GLES2;
import javax.media.opengl.GLContext;
import javax.media.opengl.GLException;

import jogamp.opengl.Debug;

import com.jogamp.common.nio.Buffers;
import com.jogamp.common.util.IOUtil;
import com.jogamp.common.util.VersionNumber;

/**
 * Convenient shader code class to use and instantiate vertex or fragment programs.
 * <p>
 * A documented example of how to use this code is available
 * {@link #create(GL2ES2, int, Class, String, String, String, boolean) here} and
 * {@link #create(GL2ES2, int, int, Class, String, String[], String, String) here}.
 * </p>
 * <p>
 * Support for {@link GL4#GL_TESS_CONTROL_SHADER} and {@link GL4#GL_TESS_EVALUATION_SHADER}
 * was added since 2.2.1.
 * </p>
 */
public class ShaderCode {
    public static final boolean DEBUG_CODE = Debug.isPropertyDefined("jogl.debug.GLSLCode", true);

    /** Unique resource suffix for {@link GL2ES2#GL_VERTEX_SHADER} in source code: <code>{@value}</code> */
    public static final String SUFFIX_VERTEX_SOURCE   =  "vp" ;

    /** Unique resource suffix for {@link GL2ES2#GL_VERTEX_SHADER} in binary: <code>{@value}</code> */
    public static final String SUFFIX_VERTEX_BINARY   = "bvp" ;

    /** Unique resource suffix for {@link GL3#GL_GEOMETRY_SHADER} in source code: <code>{@value}</code> */
    public static final String SUFFIX_GEOMETRY_SOURCE =  "gp" ;

    /** Unique resource suffix for {@link GL3#GL_GEOMETRY_SHADER} in binary: <code>{@value}</code> */
    public static final String SUFFIX_GEOMETRY_BINARY = "bgp" ;

    /**
     * Unique resource suffix for {@link GL4#GL_TESS_CONTROL_SHADER} in source code: <code>{@value}</code>
     * @since 2.2.1
     */
    public static final String SUFFIX_TESS_CONTROL_SOURCE =  "tcp" ;

    /**
     * Unique resource suffix for {@link GL4#GL_TESS_CONTROL_SHADER} in binary: <code>{@value}</code>
     * @since 2.2.1
     */
    public static final String SUFFIX_TESS_CONTROL_BINARY = "btcp" ;

    /**
     * Unique resource suffix for {@link GL4#GL_TESS_EVALUATION_SHADER} in source code: <code>{@value}</code>
     * @since 2.2.1
     */
    public static final String SUFFIX_TESS_EVALUATION_SOURCE =  "tep" ;

    /**
     * Unique resource suffix for {@link GL4#GL_TESS_EVALUATION_SHADER} in binary: <code>{@value}</code>
     * @since 2.2.1
     */
    public static final String SUFFIX_TESS_EVALUATION_BINARY = "btep" ;

    /** Unique resource suffix for {@link GL2ES2#GL_FRAGMENT_SHADER} in source code: <code>{@value}</code> */
    public static final String SUFFIX_FRAGMENT_SOURCE =  "fp" ;

    /** Unique resource suffix for {@link GL2ES2#GL_FRAGMENT_SHADER} in binary: <code>{@value}</code> */
    public static final String SUFFIX_FRAGMENT_BINARY = "bfp" ;

    /** Unique relative path for binary shader resources for {@link GLES2#GL_NVIDIA_PLATFORM_BINARY_NV NVIDIA}: <code>{@value}</code> */
    public static final String SUB_PATH_NVIDIA = "nvidia" ;

    /**
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param count number of shaders
     * @param source CharSequence array containing the shader sources, organized as <code>source[count][strings-per-shader]</code>.
     *               May be either an immutable <code>String</code> - or mutable <code>StringBuilder</code> array.
     *
     * @throws IllegalArgumentException if <code>count</count> and <code>source.length</code> do not match
     */
    public ShaderCode(final int type, final int count, final CharSequence[][] source) {
        if(source.length != count) {
            throw new IllegalArgumentException("shader number ("+count+") and sourceFiles array ("+source.length+") of different lenght.");
        }
        switch (type) {
            case GL2ES2.GL_VERTEX_SHADER:
            case GL2ES2.GL_FRAGMENT_SHADER:
            case GL3.GL_GEOMETRY_SHADER:
            case GL4.GL_TESS_CONTROL_SHADER:
            case GL4.GL_TESS_EVALUATION_SHADER:
                break;
            default:
                throw new GLException("Unknown shader type: "+type);
        }
        shaderSource = source;
        shaderBinaryFormat = -1;
        shaderBinary = null;
        shaderType   = type;
        shader = Buffers.newDirectIntBuffer(count);
        id = getNextID();

        if(DEBUG_CODE) {
            System.out.println("Created: "+toString());
            // dumpShaderSource(System.out); // already done in readShaderSource
        }
    }

    /**
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param count number of shaders
     * @param binary binary buffer containing the shader binaries,
     */
    public ShaderCode(final int type, final int count, final int binFormat, final Buffer binary) {
        switch (type) {
            case GL2ES2.GL_VERTEX_SHADER:
            case GL2ES2.GL_FRAGMENT_SHADER:
            case GL3.GL_GEOMETRY_SHADER:
            case GL4.GL_TESS_CONTROL_SHADER:
            case GL4.GL_TESS_EVALUATION_SHADER:
                break;
            default:
                throw new GLException("Unknown shader type: "+type);
        }
        shaderSource = null;
        shaderBinaryFormat = binFormat;
        shaderBinary = binary;
        shaderType   = type;
        shader = Buffers.newDirectIntBuffer(count);
        id = getNextID();
    }

    /**
     * Creates a complete {@link ShaderCode} object while reading all shader source of <code>sourceFiles</code>,
     * which location is resolved using the <code>context</code> class, see {@link #readShaderSource(Class, String)}.
     *
     * @param gl current GL object to determine whether a shader compiler is available. If null, no validation is performed.
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param count number of shaders
     * @param context class used to help resolving the source location
     * @param sourceFiles array of source locations, organized as <code>sourceFiles[count]</code>
     * @param mutableStringBuilder if <code>true</code> method returns a mutable <code>StringBuilder</code> instance
     *                        which can be edited later on at the costs of a String conversion when passing to
     *                        {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}.
     *                        If <code>false</code> method returns an immutable <code>String</code> instance,
     *                        which can be passed to {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}
     *                        at no additional costs.
     *
     * @throws IllegalArgumentException if <code>count</count> and <code>sourceFiles.length</code> do not match
     * @see #readShaderSource(Class, String)
     */
    public static ShaderCode create(final GL2ES2 gl, final int type, final int count, final Class<?> context, final String[] sourceFiles, final boolean mutableStringBuilder) {
        if(null != gl && !ShaderUtil.isShaderCompilerAvailable(gl)) {
            return null;
        }

        CharSequence[][] shaderSources = null;
        if(null!=sourceFiles) {
            // sourceFiles.length and count is validated in ctor
            shaderSources = new CharSequence[sourceFiles.length][1];
            for(int i=0; i<sourceFiles.length; i++) {
                try {
                    shaderSources[i][0] = readShaderSource(context, sourceFiles[i], mutableStringBuilder);
                } catch (final IOException ioe) {
                    throw new RuntimeException("readShaderSource("+sourceFiles[i]+") error: ", ioe);
                }
                if(null == shaderSources[i][0]) {
                    shaderSources = null;
                }
            }
        }
        if(null==shaderSources) {
            return null;
        }
        return new ShaderCode(type, count, shaderSources);
    }

    /**
     * Creates a complete {@link ShaderCode} object while reading the shader binary of <code>binaryFile</code>,
     * which location is resolved using the <code>context</code> class, see {@link #readShaderBinary(Class, String)}.
     *
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param count number of shaders
     * @param context class used to help resolving the source location
     * @param binFormat a valid native binary format as they can be queried by {@link ShaderUtil#getShaderBinaryFormats(GL)}.
     * @param sourceFiles array of source locations, organized as <code>sourceFiles[count]</code>
     *
     * @see #readShaderBinary(Class, String)
     * @see ShaderUtil#getShaderBinaryFormats(GL)
     */
    public static ShaderCode create(final int type, final int count, final Class<?> context, int binFormat, final String binaryFile) {
        ByteBuffer shaderBinary = null;
        if(null!=binaryFile && 0<=binFormat) {
            try {
                shaderBinary = readShaderBinary(context, binaryFile);
            } catch (final IOException ioe) {
                throw new RuntimeException("readShaderBinary("+binaryFile+") error: ", ioe);
            }
            if(null == shaderBinary) {
                binFormat = -1;
            }
        }
        if(null==shaderBinary) {
            return null;
        }
        return new ShaderCode(type, count, binFormat, shaderBinary);
    }

    /**
     * Returns a unique suffix for shader resources as follows:
     * <ul>
     *   <li>Source<ul>
     *     <li>{@link GL2ES2#GL_VERTEX_SHADER vertex}: {@link #SUFFIX_VERTEX_SOURCE}</li>
     *     <li>{@link GL2ES2#GL_FRAGMENT_SHADER fragment}: {@link #SUFFIX_FRAGMENT_SOURCE}</li>
     *     <li>{@link GL3#GL_GEOMETRY_SHADER geometry}: {@link #SUFFIX_GEOMETRY_SOURCE}</li>
     *     <li>{@link GL4#GL_TESS_CONTROL_SHADER tess-ctrl}: {@link #SUFFIX_TESS_CONTROL_SOURCE}</li>
     *     <li>{@link GL4#GL_TESS_EVALUATION_SHADER tess-eval}: {@link #SUFFIX_TESS_EVALUATION_SOURCE}</li>
     *     </ul></li>
     *   <li>Binary<ul>
     *     <li>{@link GL2ES2#GL_VERTEX_SHADER vertex}: {@link #SUFFIX_VERTEX_BINARY}</li>
     *     <li>{@link GL2ES2#GL_FRAGMENT_SHADER fragment}: {@link #SUFFIX_FRAGMENT_BINARY}</li>
     *     <li>{@link GL3#GL_GEOMETRY_SHADER geometry}: {@link #SUFFIX_GEOMETRY_BINARY}</li>
     *     <li>{@link GL4#GL_TESS_CONTROL_SHADER tess-ctrl}: {@link #SUFFIX_TESS_CONTROL_BINARY}</li>
     *     <li>{@link GL4#GL_TESS_EVALUATION_SHADER tess-eval}: {@link #SUFFIX_TESS_EVALUATION_BINARY}</li>
     *     </ul></li>
     * </ul>
     * @param binary true for a binary resource, false for a source resource
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     *
     * @throws GLException if <code>type</code> is not supported
     *
     * @see #create(GL2ES2, int, Class, String, String, String, boolean)
     */
    public static String getFileSuffix(final boolean binary, final int type) {
        switch (type) {
            case GL2ES2.GL_VERTEX_SHADER:
                return binary?SUFFIX_VERTEX_BINARY:SUFFIX_VERTEX_SOURCE;
            case GL2ES2.GL_FRAGMENT_SHADER:
                return binary?SUFFIX_FRAGMENT_BINARY:SUFFIX_FRAGMENT_SOURCE;
            case GL3.GL_GEOMETRY_SHADER:
                return binary?SUFFIX_GEOMETRY_BINARY:SUFFIX_GEOMETRY_SOURCE;
            case GL4.GL_TESS_CONTROL_SHADER:
                return binary?SUFFIX_TESS_CONTROL_BINARY:SUFFIX_TESS_CONTROL_SOURCE;
            case GL4.GL_TESS_EVALUATION_SHADER:
                return binary?SUFFIX_TESS_EVALUATION_BINARY:SUFFIX_TESS_EVALUATION_SOURCE;
            default:
                throw new GLException("illegal shader type: "+type);
        }
    }

    /**
     * Returns a unique relative path for binary shader resources as follows:
     * <ul>
     *   <li>{@link GLES2#GL_NVIDIA_PLATFORM_BINARY_NV NVIDIA}: {@link #SUB_PATH_NVIDIA}</li>
     * </ul>
     *
     * @throws GLException if <code>binFormat</code> is not supported
     *
     * @see #create(GL2ES2, int, Class, String, String, String, boolean)
     */
    public static String getBinarySubPath(final int binFormat) {
        switch (binFormat) {
            case GLES2.GL_NVIDIA_PLATFORM_BINARY_NV:
                return SUB_PATH_NVIDIA;
            default:
                throw new GLException("unsupported binary format: "+binFormat);
        }
    }

    /**
     * Convenient creation method for instantiating a complete {@link ShaderCode} object
     * either from source code using {@link #create(GL2ES2, int, int, Class, String[])},
     * or from a binary code using {@link #create(int, int, Class, int, String)},
     * whatever is available first.
     * <p>
     * The source and binary location names are expected w/o suffixes which are
     * resolved and appended using {@link #getFileSuffix(boolean, int)}.
     * </p>
     * <p>
     * Additionally, the binary resource is expected within a subfolder of <code>binRoot</code>
     * which reflects the vendor specific binary format, see {@link #getBinarySubPath(int)}.
     * All {@link ShaderUtil#getShaderBinaryFormats(GL)} are being iterated
     * using the binary subfolder, the first existing resource is being used.
     * </p>
     *
     * Example:
     * <pre>
     *   Your std JVM layout (plain or within a JAR):
     *
     *      org/test/glsl/MyShaderTest.class
     *      org/test/glsl/shader/vertex.vp
     *      org/test/glsl/shader/fragment.fp
     *      org/test/glsl/shader/bin/nvidia/vertex.bvp
     *      org/test/glsl/shader/bin/nvidia/fragment.bfp
     *
     *   Your Android APK layout:
     *
     *      classes.dex
     *      assets/org/test/glsl/shader/vertex.vp
     *      assets/org/test/glsl/shader/fragment.fp
     *      assets/org/test/glsl/shader/bin/nvidia/vertex.bvp
     *      assets/org/test/glsl/shader/bin/nvidia/fragment.bfp
     *      ...
     *
     *   Your invocation in org/test/glsl/MyShaderTest.java:
     *
     *      ShaderCode vp0 = ShaderCode.create(gl, GL2ES2.GL_VERTEX_SHADER, 1, this.getClass(),
     *                                         "shader", new String[] { "vertex" }, "shader/bin", "vertex");
     *      ShaderCode fp0 = ShaderCode.create(gl, GL2ES2.GL_FRAGMENT_SHADER, 1, this.getClass(),
     *                                         "shader", new String[] { "vertex" }, "shader/bin", "fragment");
     *      ShaderProgram sp0 = new ShaderProgram();
     *      sp0.add(gl, vp0, System.err);
     *      sp0.add(gl, fp0, System.err);
     *      st.attachShaderProgram(gl, sp0, true);
     * </pre>
     * A simplified entry point is {@link #create(GL2ES2, int, Class, String, String, String, boolean)}.
     *
     * <p>
     * The location is finally being resolved using the <code>context</code> class, see {@link #readShaderBinary(Class, String)}.
     * </p>
     *
     * @param gl current GL object to determine whether a shader compiler is available (if <code>source</code> is used),
     *           or to determine the shader binary format (if <code>binary</code> is used).
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param count number of shaders
     * @param context class used to help resolving the source and binary location
     * @param srcRoot relative <i>root</i> path for <code>srcBasenames</code> optional
     * @param srcBasenames basenames w/o path or suffix relative to <code>srcRoot</code> for the shader's source code
     * @param binRoot relative <i>root</i> path for <code>binBasenames</code>
     * @param binBasename basename w/o path or suffix relative to <code>binRoot</code> for the shader's binary code
     * @param mutableStringBuilder if <code>true</code> method returns a mutable <code>StringBuilder</code> instance
     *                        which can be edited later on at the costs of a String conversion when passing to
     *                        {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}.
     *                        If <code>false</code> method returns an immutable <code>String</code> instance,
     *                        which can be passed to {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}
     *                        at no additional costs.
     *
     * @throws IllegalArgumentException if <code>count</count> and <code>srcBasenames.length</code> do not match
     *
     * @see #create(GL2ES2, int, int, Class, String[])
     * @see #create(int, int, Class, int, String)
     * @see #readShaderSource(Class, String)
     * @see #getFileSuffix(boolean, int)
     * @see ShaderUtil#getShaderBinaryFormats(GL)
     * @see #getBinarySubPath(int)
     */
    public static ShaderCode create(final GL2ES2 gl, final int type, final int count, final Class<?> context,
                                    final String srcRoot, final String[] srcBasenames, final String binRoot, final String binBasename,
                                    final boolean mutableStringBuilder) {
        ShaderCode res = null;
        final String srcPath[];
        String srcPathString = null;
        String binFileName = null;

        if( null!=srcBasenames && ShaderUtil.isShaderCompilerAvailable(gl) ) {
            srcPath = new String[srcBasenames.length];
            final String srcSuffix = getFileSuffix(false, type);
            if( null != srcRoot && srcRoot.length() > 0 ) {
                for(int i=0; i<srcPath.length; i++) {
                    srcPath[i] = srcRoot + '/' + srcBasenames[i] + "." + srcSuffix;
                }
            } else {
                for(int i=0; i<srcPath.length; i++) {
                    srcPath[i] = srcBasenames[i] + "." + srcSuffix;
                }
            }
            res = create(gl, type, count, context, srcPath, mutableStringBuilder);
            if(null!=res) {
                return res;
            }
            srcPathString = Arrays.toString(srcPath);
        } else {
            srcPath = null;
        }
        if( null!=binBasename ) {
            final Set<Integer> binFmts = ShaderUtil.getShaderBinaryFormats(gl);
            final String binSuffix = getFileSuffix(true, type);
            for(final Iterator<Integer> iter=binFmts.iterator(); iter.hasNext(); ) {
                final int bFmt = iter.next().intValue();
                final String bFmtPath = getBinarySubPath(bFmt);
                if(null==bFmtPath) continue;
                binFileName = binRoot + '/' + bFmtPath + '/' + binBasename + "." + binSuffix;
                res = create(type, count, context, bFmt, binFileName);
                if(null!=res) {
                    return res;
                }
            }
        }
        throw new GLException("No shader code found (source nor binary) for src: "+srcPathString+
                              ", bin: "+binFileName);
    }

    /**
     * Simplified variation of {@link #create(GL2ES2, int, int, Class, String, String[], String, String, boolean)}.
     * <p>
     * Example:
     * <pre>
     *   Your std JVM layout (plain or within a JAR):
     *
     *      org/test/glsl/MyShaderTest.class
     *      org/test/glsl/shader/vertex.vp
     *      org/test/glsl/shader/fragment.fp
     *      org/test/glsl/shader/bin/nvidia/vertex.bvp
     *      org/test/glsl/shader/bin/nvidia/fragment.bfp
     *
     *   Your Android APK layout:
     *
     *      classes.dex
     *      assets/org/test/glsl/shader/vertex.vp
     *      assets/org/test/glsl/shader/fragment.fp
     *      assets/org/test/glsl/shader/bin/nvidia/vertex.bvp
     *      assets/org/test/glsl/shader/bin/nvidia/fragment.bfp
     *      ...
     *
     *   Your invocation in org/test/glsl/MyShaderTest.java:
     *
     *      ShaderCode vp0 = ShaderCode.create(gl, GL2ES2.GL_VERTEX_SHADER, this.getClass(),
     *                                         "shader", "shader/bin", "vertex");
     *      ShaderCode fp0 = ShaderCode.create(gl, GL2ES2.GL_FRAGMENT_SHADER, this.getClass(),
     *                                         "shader", "shader/bin", "fragment");
     *      ShaderProgram sp0 = new ShaderProgram();
     *      sp0.add(gl, vp0, System.err);
     *      sp0.add(gl, fp0, System.err);
     *      st.attachShaderProgram(gl, sp0, true);
     * </pre>
     * </p>
     *
     * @param gl current GL object to determine whether a shader compiler is available (if <code>source</code> is used),
     *           or to determine the shader binary format (if <code>binary</code> is used).
     * @param type either {@link GL2ES2#GL_VERTEX_SHADER}, {@link GL2ES2#GL_FRAGMENT_SHADER}, {@link GL3#GL_GEOMETRY_SHADER},
     *                    {@link GL4#GL_TESS_CONTROL_SHADER} or {@link GL4#GL_TESS_EVALUATION_SHADER}.
     * @param context class used to help resolving the source and binary location
     * @param srcRoot relative <i>root</i> path for <code>basename</code> optional
     * @param binRoot relative <i>root</i> path for <code>basename</code>
     * @param mutableStringBuilder TODO
     * @param basenames basename w/o path or suffix relative to <code>srcRoot</code> and <code>binRoot</code>
     *                  for the shader's source and binary code.
     * @param mutableStringBuilder if <code>true</code> method returns a mutable <code>StringBuilder</code> instance
     *                        which can be edited later on at the costs of a String conversion when passing to
     *                        {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}.
     *                        If <code>false</code> method returns an immutable <code>String</code> instance,
     *                        which can be passed to {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}
     *                        at no additional costs.
     * @throws IllegalArgumentException if <code>count</count> is not 1
     *
     * @see #create(GL2ES2, int, int, Class, String, String[], String, String)
     */
    public static ShaderCode create(final GL2ES2 gl, final int type, final Class<?> context,
                                    final String srcRoot, final String binRoot, final String basename, final boolean mutableStringBuilder) {
        return create(gl, type, 1, context, srcRoot, new String[] { basename }, binRoot, basename, mutableStringBuilder );
    }

    /**
     * returns the uniq shader id as an integer
     */
    public int id() { return id; }

    public int        shaderType() { return shaderType; }
    public String     shaderTypeStr() { return shaderTypeStr(shaderType); }

    public static String shaderTypeStr(final int type) {
        switch (type) {
            case GL2ES2.GL_VERTEX_SHADER:
                return "VERTEX_SHADER";
            case GL2ES2.GL_FRAGMENT_SHADER:
                return "FRAGMENT_SHADER";
            case GL3.GL_GEOMETRY_SHADER:
                return "GEOMETRY_SHADER";
            case GL4.GL_TESS_CONTROL_SHADER:
                return "TESS_CONTROL_SHADER";
            case GL4.GL_TESS_EVALUATION_SHADER:
                return "TESS_EVALUATION_SHADER";
        }
        return "UNKNOWN_SHADER";
    }

    public int shaderBinaryFormat() { return shaderBinaryFormat; }
    public Buffer shaderBinary() { return shaderBinary; }
    public CharSequence[][] shaderSource() { return shaderSource; }

    public boolean    isValid() { return valid; }

    public IntBuffer  shader() { return shader; }

    public boolean compile(final GL2ES2 gl) {
        return compile(gl, null);
    }
    public boolean compile(final GL2ES2 gl, final PrintStream verboseOut) {
        if(isValid()) return true;

        // Create & Compile the vertex/fragment shader objects
        if(null!=shaderSource) {
            if(DEBUG_CODE) {
                System.err.println("ShaderCode.compile:");
                dumpShaderSource(System.err);
            }
            valid=ShaderUtil.createAndCompileShader(gl, shader, shaderType,
                                                    shaderSource, verboseOut);
        } else if(null!=shaderBinary) {
            valid=ShaderUtil.createAndLoadShader(gl, shader, shaderType,
                                                 shaderBinaryFormat, shaderBinary, verboseOut);
        } else {
            throw new GLException("no code (source or binary)");
        }
        return valid;
    }

    public void destroy(final GL2ES2 gl) {
        if(isValid()) {
            if(null!=gl) {
                ShaderUtil.deleteShader(gl, shader());
            }
            valid=false;
        }
        if(null!=shaderBinary) {
            shaderBinary.clear();
            shaderBinary=null;
        }
        shaderSource=null;
        shaderBinaryFormat=-1;
        shaderType=-1;
        id=-1;
    }

    @Override
    public boolean equals(final Object obj) {
        if(this==obj) { return true; }
        if(obj instanceof ShaderCode) {
            return id()==((ShaderCode)obj).id();
        }
        return false;
    }
    @Override
    public int hashCode() {
        return id;
    }
    @Override
    public String toString() {
        final StringBuilder buf = new StringBuilder("ShaderCode[id="+id+", type="+shaderTypeStr()+", valid="+valid+", shader: ");
        for(int i=0; i<shader.remaining(); i++) {
            buf.append(" "+shader.get(i));
        }
        if(null!=shaderSource) {
            buf.append(", source]");
        } else if(null!=shaderBinary) {
            buf.append(", binary "+shaderBinary+"]");
        }
        return buf.toString();
    }

    public void dumpShaderSource(final PrintStream out) {
        if(null==shaderSource) {
            out.println("<no shader source>");
            return;
        }
        final int sourceCount = shaderSource.length;
        final int shaderCount = (null!=shader)?shader.capacity():0;
        for(int i=0; i<shaderCount; i++) {
            out.println("");
            out.println("Shader #"+i+"/"+shaderCount+" name "+shader.get(i));
            out.println("--------------------------------------------------------------");
            if(i>=sourceCount) {
                out.println("<no shader source>");
            } else {
                final CharSequence[] src = shaderSource[i];
                int lineno=0;

                for(int j=0; j<src.length; j++) {
                    out.printf("%4d: // Segment %d/%d: \n", lineno, j, src.length);
                    final BufferedReader reader = new BufferedReader(new StringReader(src[j].toString()));
                    String line = null;
                    try {
                        while ((line = reader.readLine()) != null) {
                            lineno++;
                            out.printf("%4d: %s\n", lineno, line);
                        }
                    } catch (final IOException e) { /* impossible .. StringReader */ }
                }
            }
            out.println("--------------------------------------------------------------");
        }
    }

    /**
     * Adds <code>data</code> after the line containing <code>tag</code>.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     *
     * @param shaderIdx the shader index to be used.
     * @param tag search string
     * @param fromIndex start search <code>tag</code> begininig with this index
     * @param data the text to be inserted. Shall end with an EOL '\n' character.
     * @return index after the inserted <code>data</code>
     *
     * @throws IllegalStateException if the shader source's CharSequence is immutable, i.e. not of type <code>StringBuilder</code>
     */
    public int insertShaderSource(final int shaderIdx, final String tag, final int fromIndex, final CharSequence data) {
        if(null==shaderSource) {
            throw new IllegalStateException("no shader source");
        }
        final int shaderCount = (null!=shader)?shader.capacity():0;
        if(0>shaderIdx || shaderIdx>=shaderCount) {
            throw new IndexOutOfBoundsException("shaderIdx not within shader bounds [0.."+(shaderCount-1)+"]: "+shaderIdx);
        }
        final int sourceCount = shaderSource.length;
        if(shaderIdx>=sourceCount) {
            throw new IndexOutOfBoundsException("shaderIdx not within source bounds [0.."+(sourceCount-1)+"]: "+shaderIdx);
        }
        final CharSequence[] src = shaderSource[shaderIdx];
        int curEndIndex = 0;
        for(int j=0; j<src.length; j++) {
            if( !(src[j] instanceof StringBuilder) ) {
                throw new IllegalStateException("shader source not a mutable StringBuilder, but CharSequence of type: "+src[j].getClass().getName());
            }
            final StringBuilder sb = (StringBuilder)src[j];
            curEndIndex += sb.length();
            if(fromIndex < curEndIndex) {
                int insertIdx = sb.indexOf(tag, fromIndex);
                if(0<=insertIdx) {
                    insertIdx += tag.length();
                    int eol = sb.indexOf("\n", insertIdx); // eol: covers \n and \r\n
                    if(0>eol) {
                        eol = sb.indexOf("\r", insertIdx); // eol: covers \r 'only'
                    }
                    if(0<eol) {
                        insertIdx = eol+1;  // eol found
                    } else {
                        sb.insert(insertIdx, "\n"); // add eol
                        insertIdx++;
                    }
                    sb.insert(insertIdx, data);
                    return insertIdx+data.length();
                }
            }
        }
        return -1;
    }

    /**
     * Replaces <code>oldName</code> with <code>newName</code> in all shader sources.
     * <p>
     * In case <code>oldName</code> and <code>newName</code> are equal, no action is performed.
     * </p>
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     *
     * @param oldName the to be replace string
     * @param newName the replacement string
     * @return the number of replacements
     *
     * @throws IllegalStateException if the shader source's CharSequence is immutable, i.e. not of type <code>StringBuilder</code>
     */
    public int replaceInShaderSource(final String oldName, final String newName) {
        if(null==shaderSource) {
            throw new IllegalStateException("no shader source");
        }
        if(oldName == newName || oldName.equals(newName)) {
            return 0;
        }
        final int oldNameLen = oldName.length();
        final int newNameLen = newName.length();
        int num = 0;
        final int sourceCount = shaderSource.length;
        for(int shaderIdx = 0; shaderIdx<sourceCount; shaderIdx++) {
            final CharSequence[] src = shaderSource[shaderIdx];
            for(int j=0; j<src.length; j++) {
                if( !(src[j] instanceof StringBuilder) ) {
                    throw new IllegalStateException("shader source not a mutable StringBuilder, but CharSequence of type: "+src[j].getClass().getName());
                }
                final StringBuilder sb = (StringBuilder)src[j];
                int curPos = 0;
                while(curPos<sb.length()-oldNameLen+1) {
                    final int startIdx = sb.indexOf(oldName, curPos);
                    if(0<=startIdx) {
                        final int endIdx = startIdx + oldNameLen;
                        sb.replace(startIdx, endIdx, newName);
                        curPos = startIdx + newNameLen;
                        num++;
                    } else {
                        curPos = sb.length();
                    }
                }
            }
        }
        return num;
    }

    /**
     * Adds <code>data</code> at <code>position</code> in shader source for shader <code>shaderIdx</code>.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     *
     * @param shaderIdx the shader index to be used.
     * @param position in shader source segments of shader <code>shaderIdx</code>, -1 will append data
     * @param data the text to be inserted. Shall end with an EOL '\n' character
     * @return index after the inserted <code>data</code>
     *
     * @throws IllegalStateException if the shader source's CharSequence is immutable, i.e. not of type <code>StringBuilder</code>
     */
    public int insertShaderSource(final int shaderIdx, int position, final CharSequence data) {
        if(null==shaderSource) {
            throw new IllegalStateException("no shader source");
        }
        final int shaderCount = (null!=shader)?shader.capacity():0;
        if(0>shaderIdx || shaderIdx>=shaderCount) {
            throw new IndexOutOfBoundsException("shaderIdx not within shader bounds [0.."+(shaderCount-1)+"]: "+shaderIdx);
        }
        final int sourceCount = shaderSource.length;
        if(shaderIdx>=sourceCount) {
            throw new IndexOutOfBoundsException("shaderIdx not within source bounds [0.."+(sourceCount-1)+"]: "+shaderIdx);
        }
        final CharSequence[] src = shaderSource[shaderIdx];
        int curEndIndex = 0;
        for(int j=0; j<src.length; j++) {
            if( !(src[j] instanceof StringBuilder) ) {
                throw new IllegalStateException("shader source not a mutable StringBuilder, but CharSequence of type: "+src[j].getClass().getName());
            }
            final StringBuilder sb = (StringBuilder)src[j];
            curEndIndex += sb.length();
            if( 0 > position && j == src.length - 1 ) {
                position = curEndIndex;
            }
            if(0 <= position && position <= curEndIndex ) {
                sb.insert(position, data);
                return position+data.length();
            }
        }
        return position;
    }

    /**
     * Adds shader source located in <code>path</code>,
     * either relative to the <code>context</code> class or absolute <i>as-is</i>
     * at <code>position</code> in shader source for shader <code>shaderIdx</code>.
     * <p>
     * Final location lookup is performed via {@link ClassLoader#getResource(String)} and {@link ClassLoader#getSystemResource(String)},
     * see {@link IOUtil#getResource(Class, String)}.
     * </p>
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     *
     * @param shaderIdx the shader index to be used.
     * @param position in shader source segments of shader <code>shaderIdx</code>, -1 will append data
     * @param context class used to help resolve the source location
     * @param path location of shader source
     * @return index after the inserted code.
     * @throws IOException
     * @throws IllegalStateException if the shader source's CharSequence is immutable, i.e. not of type <code>StringBuilder</code>
     * @see IOUtil#getResource(Class, String)
     */
    public int insertShaderSource(final int shaderIdx, final int position, final Class<?> context, final String path) throws IOException {
        final CharSequence data = readShaderSource(context, path, true);
        if( null != data ) {
            return insertShaderSource(shaderIdx, position, data);
        } else {
            return position;
        }
    }

    @SuppressWarnings("resource")
    private static int readShaderSource(final Class<?> context, final URLConnection conn, final StringBuilder result, int lineno) throws IOException  {
        if(DEBUG_CODE) {
            if(0 == lineno) {
                result.append("// "+conn.getURL().toExternalForm()+"\n");
            } else {
                result.append("// included @ line "+lineno+": "+conn.getURL().toExternalForm()+"\n");
            }
        }
        final BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        try {
            String line = null;
            while ((line = reader.readLine()) != null) {
                lineno++;
                if (line.startsWith("#include ")) {
                    final String includeFile = line.substring(9).trim();
                    URLConnection nextConn = null;

                    // Try relative of current shader location
                    nextConn = IOUtil.openURL(IOUtil.getRelativeOf(conn.getURL(), includeFile), "ShaderCode.relativeOf ");
                    if (nextConn == null) {
                        // Try relative of class and absolute
                        nextConn = IOUtil.getResource(context, includeFile);
                    }
                    if (nextConn == null) {
                        // Fail
                        throw new FileNotFoundException("Can't find include file " + includeFile);
                    }
                    lineno = readShaderSource(context, nextConn, result, lineno);
                } else {
                    result.append(line + "\n");
                }
            }
        } finally {
            IOUtil.close(reader, false);
        }
        return lineno;
    }

    /**
     *
     * @param context
     * @param conn
     * @param result
     * @throws IOException
     */
    public static void readShaderSource(final Class<?> context, final URLConnection conn, final StringBuilder result) throws IOException {
        readShaderSource(context, conn, result, 0);
    }

    /**
     * Reads shader source located in <code>path</code>,
     * either relative to the <code>context</code> class or absolute <i>as-is</i>.
     * <p>
     * Final location lookup is performed via {@link ClassLoader#getResource(String)} and {@link ClassLoader#getSystemResource(String)},
     * see {@link IOUtil#getResource(Class, String)}.
     * </p>
     *
     * @param context class used to help resolve the source location
     * @param path location of shader source
     * @param mutableStringBuilder if <code>true</code> method returns a mutable <code>StringBuilder</code> instance
     *                        which can be edited later on at the costs of a String conversion when passing to
     *                        {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}.
     *                        If <code>false</code> method returns an immutable <code>String</code> instance,
     *                        which can be passed to {@link GL2ES2#glShaderSource(int, int, String[], IntBuffer)}
     *                        at no additional costs.
     * @throws IOException
     *
     * @see IOUtil#getResource(Class, String)
     */
    public static CharSequence readShaderSource(final Class<?> context, final String path, final boolean mutableStringBuilder) throws IOException {
        final URLConnection conn = IOUtil.getResource(context, path);
        if (conn == null) {
            return null;
        }
        final StringBuilder result = new StringBuilder();
        readShaderSource(context, conn, result);
        return mutableStringBuilder ? result : result.toString();
    }

    /**
     * Reads shader binary located in <code>path</code>,
     * either relative to the <code>context</code> class or absolute <i>as-is</i>.
     * <p>
     * Final location lookup is perfomed via {@link ClassLoader#getResource(String)} and {@link ClassLoader#getSystemResource(String)},
     * see {@link IOUtil#getResource(Class, String)}.
     * </p>
     *
     * @param context class used to help resolve the source location
     * @param path location of shader binary
     * @throws IOException
     *
     * @see IOUtil#getResource(Class, String)
     */
    public static ByteBuffer readShaderBinary(final Class<?> context, final String path) throws IOException {
        final URLConnection conn = IOUtil.getResource(context, path);
        if (conn == null) {
            return null;
        }
        final BufferedInputStream bis = new BufferedInputStream( conn.getInputStream() );
        try {
            return IOUtil.copyStream2ByteBuffer( bis );
        } finally {
            IOUtil.close(bis, false);
        }
    }

    // Shall we use: #ifdef GL_FRAGMENT_PRECISION_HIGH .. #endif for using highp in fragment shader if avail ?
    /** Default precision of {@link GL#isGLES2() ES2} for {@link GL2ES2#GL_VERTEX_SHADER vertex-shader}: {@value #es2_default_precision_vp} */
    public static final String es2_default_precision_vp = "\nprecision highp float;\nprecision highp int;\n/*precision lowp sampler2D;*/\n/*precision lowp samplerCube;*/\n";
    /** Default precision of {@link GL#isGLES2() ES2} for {@link GL2ES2#GL_FRAGMENT_SHADER fragment-shader}: {@value #es2_default_precision_fp} */
    public static final String es2_default_precision_fp = "\nprecision mediump float;\nprecision mediump int;\n/*precision lowp sampler2D;*/\n/*precision lowp samplerCube;*/\n";

    /** Default precision of {@link GL#isGLES3() ES3} for {@link GL2ES2#GL_VERTEX_SHADER vertex-shader}: {@value #es3_default_precision_vp} */
    public static final String es3_default_precision_vp = es2_default_precision_vp;
    /**
     * Default precision of {@link GL#isGLES3() ES3} for {@link GL2ES2#GL_FRAGMENT_SHADER fragment-shader}: {@value #es3_default_precision_fp},
     * same as for {@link GL2ES2#GL_VERTEX_SHADER vertex-shader}, i.e {@link #es3_default_precision_vp},
     * due to ES 3.x requirements of using same precision for uniforms!
     */
    public static final String es3_default_precision_fp = es3_default_precision_vp;

    /** Default precision of GLSL &ge; 1.30 as required until &lt; 1.50 for {@link GL2ES2#GL_VERTEX_SHADER vertex-shader} or {@link GL3#GL_GEOMETRY_SHADER geometry-shader}: {@value #gl3_default_precision_vp_gp}. See GLSL Spec 1.30-1.50 Section 4.5.3. */
    public static final String gl3_default_precision_vp_gp = "\nprecision highp float;\nprecision highp int;\n";
    /** Default precision of GLSL &ge; 1.30 as required until &lt; 1.50 for {@link GL2ES2#GL_FRAGMENT_SHADER fragment-shader}: {@value #gl3_default_precision_fp}. See GLSL Spec 1.30-1.50 Section 4.5.3. */
    public static final String gl3_default_precision_fp = "\nprecision highp float;\nprecision mediump int;\n/*precision mediump sampler2D;*/\n";

    /** <i>Behavior</i> for GLSL extension directive, see {@link #createExtensionDirective(String, String)}, value {@value}. */
    public static final String REQUIRE = "require";
    /** <i>Behavior</i> for GLSL extension directive, see {@link #createExtensionDirective(String, String)}, value {@value}. */
    public static final String ENABLE = "enable";
    /** <i>Behavior</i> for GLSL extension directive, see {@link #createExtensionDirective(String, String)}, value {@value}. */
    public static final String DISABLE = "disable";
    /** <i>Behavior</i> for GLSL extension directive, see {@link #createExtensionDirective(String, String)}, value {@value}. */
    public static final String WARN = "warn";

    /**
     * Creates a GLSL extension directive.
     * <p>
     * Prefer {@link #ENABLE} over {@link #REQUIRE}, since the latter will force a failure if not supported.
     * </p>
     *
     * @param extensionName
     * @param behavior shall be either {@link #REQUIRE}, {@link #ENABLE}, {@link #DISABLE} or {@link #WARN}
     * @return the complete extension directive
     */
    public static String createExtensionDirective(final String extensionName, final String behavior) {
        return "#extension " + extensionName + " : " + behavior + "\n";
    }

    /**
     * Add GLSL version at the head of this shader source code.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     * @param gl a GL context, which must have been made current once
     * @return the index after the inserted data, maybe 0 if nothing has be inserted.
     */
    public final int addGLSLVersion(final GL2ES2 gl) {
        return insertShaderSource(0, 0, gl.getContext().getGLSLVersionString());
    }

    /**
     * Adds default precision to source code at given position if required, i.e.
     * {@link #es2_default_precision_vp}, {@link #es2_default_precision_fp},
     * {@link #gl3_default_precision_vp_gp}, {@link #gl3_default_precision_fp} or none,
     * depending on the {@link GLContext#getGLSLVersionNumber() GLSL version} being used.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     * @param gl a GL context, which must have been made current once
     * @param pos position within this mutable shader source.
     * @return the index after the inserted data, maybe 0 if nothing has be inserted.
     */
    public final int addDefaultShaderPrecision(final GL2ES2 gl, int pos) {
        final String defaultPrecision;
        if( gl.isGLES3() ) {
            switch ( shaderType ) {
                case GL2ES2.GL_VERTEX_SHADER:
                    defaultPrecision = es3_default_precision_vp; break;
                case GL2ES2.GL_FRAGMENT_SHADER:
                    defaultPrecision = es3_default_precision_fp; break;
                default:
                    defaultPrecision = null;
                    break;
            }
        } else if( gl.isGLES2() ) {
            switch ( shaderType ) {
                case GL2ES2.GL_VERTEX_SHADER:
                    defaultPrecision = es2_default_precision_vp; break;
                case GL2ES2.GL_FRAGMENT_SHADER:
                    defaultPrecision = es2_default_precision_fp; break;
                default:
                    defaultPrecision = null;
                    break;
            }
        } else if( requiresGL3DefaultPrecision(gl) ) {
            // GLSL [ 1.30 .. 1.50 [ needs at least fragement float default precision!
            switch ( shaderType ) {
                case GL2ES2.GL_VERTEX_SHADER:
                case GL3.GL_GEOMETRY_SHADER:
                case GL4.GL_TESS_CONTROL_SHADER:
                case GL4.GL_TESS_EVALUATION_SHADER:
                    defaultPrecision = gl3_default_precision_vp_gp; break;
                case GL2ES2.GL_FRAGMENT_SHADER:
                    defaultPrecision = gl3_default_precision_fp; break;
                default:
                    defaultPrecision = null;
                    break;
            }
        } else {
            defaultPrecision = null;
        }
        if( null != defaultPrecision ) {
            pos = insertShaderSource(0, pos, defaultPrecision);
        }
        return pos;
    }

    /** Returns true, if GLSL version requires default precision, i.e. ES2 or GLSL [1.30 .. 1.50[. */
    public static final boolean requiresDefaultPrecision(final GL2ES2 gl) {
        if( gl.isGLES() ) {
            return true;
        }
        return requiresGL3DefaultPrecision(gl);
    }

    /** Returns true, if GL3 GLSL version requires default precision, i.e. GLSL [1.30 .. 1.50[. */
    public static final boolean requiresGL3DefaultPrecision(final GL2ES2 gl) {
        if( gl.isGL3() ) {
            final VersionNumber glslVersion = gl.getContext().getGLSLVersionNumber();
            return glslVersion.compareTo(GLContext.Version130) >= 0 && glslVersion.compareTo(GLContext.Version150) < 0 ;
        } else {
            return false;
        }
    }

    /**
     * Default customization of this shader source code.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     * @param gl a GL context, which must have been made current once
     * @param preludeVersion if true {@link GLContext#getGLSLVersionString()} is preluded, otherwise not.
     * @param addDefaultPrecision if <code>true</code> default precision source code line(s) are added, i.e.
     *                            {@link #es2_default_precision_vp}, {@link #es2_default_precision_fp},
     *                            {@link #gl3_default_precision_vp_gp}, {@link #gl3_default_precision_fp} or none,
     *                            depending on the {@link GLContext#getGLSLVersionNumber() GLSL version} being used.
     * @return the index after the inserted data, maybe 0 if nothing has be inserted.
     * @see #addGLSLVersion(GL2ES2)
     * @see #addDefaultShaderPrecision(GL2ES2, int)
     */
    public final int defaultShaderCustomization(final GL2ES2 gl, final boolean preludeVersion, final boolean addDefaultPrecision) {
        int pos;
        if( preludeVersion ) {
            pos = addGLSLVersion(gl);
        } else {
            pos = 0;
        }
        if( addDefaultPrecision ) {
            pos = addDefaultShaderPrecision(gl, pos);
        }
        return pos;
    }

    /**
     * Default customization of this shader source code.
     * <p>
     * Note: The shader source to be edit must be created using a mutable StringBuilder.
     * </p>
     * @param gl a GL context, which must have been made current once
     * @param preludeVersion if true {@link GLContext#getGLSLVersionString()} is preluded, otherwise not.
     * @param esDefaultPrecision optional default precision source code line(s) preluded if not null and if {@link GL#isGLES()}.
     *        You may use {@link #es2_default_precision_fp} for fragment shader and {@link #es2_default_precision_vp} for vertex shader.
     * @return the index after the inserted data, maybe 0 if nothing has be inserted.
     * @see #addGLSLVersion(GL2ES2)
     * @see #addDefaultShaderPrecision(GL2ES2, int)
     */
    public final int defaultShaderCustomization(final GL2ES2 gl, final boolean preludeVersion, final String esDefaultPrecision) {
        int pos;
        if( preludeVersion ) {
            pos = addGLSLVersion(gl);
        } else {
            pos = 0;
        }
        if( gl.isGLES() && null != esDefaultPrecision ) {
            pos = insertShaderSource(0, pos, esDefaultPrecision);
        } else {
            pos = addDefaultShaderPrecision(gl, pos);
        }
        return pos;
    }

    //----------------------------------------------------------------------
    // Internals only below this point
    //

    protected CharSequence[][] shaderSource = null;
    protected Buffer     shaderBinary = null;
    protected int        shaderBinaryFormat = -1;
    protected IntBuffer  shader = null;
    protected int        shaderType = -1;
    protected int        id = -1;

    protected boolean valid=false;

    private static synchronized int getNextID() {
        return nextID++;
    }
    protected static int nextID = 1;
}

