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