Android OpenGL 纹理绘制图像---Native实现

本文纹理贴图的native实现，是指指定纹理的功能放在了native中实现，其他流程和Java实现类似，在这里就不赘述了。再回头看一下指定纹理数据的方法：

void glTexImage2D(GLenum target,GLint level,GLint internalFormat,   GLsizei width,GLsizei height,Glint border,GLenum format,   GLenum type,const void *texles);

通过以上我们可以知道，需要指定图像的像素数据和图像的一些参数才可以指定纹理，以PNG图像为例，实现指定纹理的步骤：
（1）解析PNG文件
其实网上有很多各种版本解析PNG文件的库，基本上不需要自己实现，本文采用为Android重新包装的libpng 1.6.23，具体代码可参考github地址：https://github.com/julienr/libpng-android。
（2）获取PNG像素数据和其他一些参数

bool ParsePngFile::parse() {    std::istringstream pngDataStream(pngDataString);    const int PNG_SIG_BYTES = 8;    char pngSignature[PNG_SIG_BYTES];    pngDataStream.read(pngSignature, PNG_SIG_BYTES * sizeof(char));    if(!png_check_sig( (png_bytep)pngSignature, PNG_SIG_BYTES) )    {        return false;    }    /**     * Create and initialize the png_struct     * with the desired error handler     * functions.  If you want to use the     * default stderr and longjump method,     * you can supply NULL for the last     * three parameters.  We also supply the     * the compiler header file version, so     * that we know if the application     * was compiled with a compatible version     * of the library.  REQUIRED     */    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);    if (png_ptr == NULL)    {        return false;    }    /**     * Allocate/initialize the memory     * for image information.  REQUIRED. */    png_infop info_ptr = png_create_info_struct(png_ptr);    if (info_ptr == NULL)    {        png_destroy_read_struct(&png_ptr, NULL, NULL);        return false;    }    /**     * Set error handling if you are     * using the setjmp/longjmp method     * (this is the normal method of     * doing things with libpng).     * REQUIRED unless you  set up     * your own error handlers in     * the png_create_read_struct()     * earlier.     */    if (setjmp(png_jmpbuf(png_ptr))) {        /* Free all of the memory associated         * with the png_ptr and info_ptr */        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);        return false;    }    /**     * Set custom input stream READER / handler     */    png_set_read_fn( png_ptr, (void*)&pngDataStream, readFileCallback );    /* If we have already     * read some of the signature */    png_set_sig_bytes( png_ptr, 8 );    png_read_info( png_ptr, info_ptr);    int  _depth;    int color_type, interlace_type;    png_get_IHDR( png_ptr, info_ptr, (png_uint_32*)&_width, (png_uint_32*)&_height, &_depth, &color_type, &interlace_type, NULL, NULL );    switch(color_type)    {        case PNG_COLOR_TYPE_RGB:            _hasAlpha = false;            break;        case PNG_COLOR_TYPE_RGBA:            _hasAlpha = true;            break;        default:            return false;    }    png_size_t cols = png_get_rowbytes(png_ptr, info_ptr);    png_bytepp row_pp = new png_bytep[_height];    pngData= new char[ cols * _height ];    for( int i = 0; i < _height; ++i )    {        // note that png is ordered top to        // bottom, but OpenGL expect it bottom to top        // so the order or swapped        row_pp[i] = (png_bytep)&((char *)pngData)[ i * cols ];    }    png_read_image( png_ptr, row_pp );    png_read_end( png_ptr, info_ptr );    png_destroy_read_struct( &png_ptr, &info_ptr, 0 );    delete [] row_pp;    return true;}

（3）实现指定纹理函数

void ParsePngFile::glPngTexImage2D(int target, int level) {   if(pngData != NULL){       glTexImage2D(target, level, _hasAlpha ? GL_RGBA : GL_RGB, _width, _height, 0, _hasAlpha ? GL_RGBA : GL_RGB, GL_UNSIGNED_BYTE, pngData);   }}

附上github地址：https://github.com/qiaoyanfei/OpenGL_Image.git