[OpenGL] 获取画布背景的位图数据

// get data of canvas rendered with OpenGL
// note : need to call delete[] for *pData
bool CaptureOpenGL(int& nWidth, int& nHeight, int& nPitch, BYTE** pData)
{
static GLenum s_Format = GL_BGRA_EXT;
static int s_nBytePerPixel = 4; // 4Byte : because pixel format is GL_BGRA_EXT

nWidth = nHeight = nPitch = 0;
*pData = NULL;

GLint aViewport[4];
glGetIntegerv(GL_VIEWPORT, aViewport);

int width = aViewport[2];
int height = aViewport[3];
if ((width * height) <= 0)
return false;

int pitch = width * s_nBytePerPixel;
int len = pitch * height;
BYTE* pBuffer = new BYTE[len];
if (!pBuffer)
return false;

glPixelStorei(GL_PACK_ALIGNMENT, 1);
glPixelStorei(GL_PACK_ROW_LENGTH, 0);
glPixelStorei(GL_PACK_SKIP_ROWS, 0);
glPixelStorei(GL_PACK_SKIP_PIXELS, 0);

GLenum lastBuffer;
glGetIntegerv(GL_READ_BUFFER, (GLint*)&lastBuffer);
glReadBuffer(GL_FRONT);
glReadPixels(0, 0, width, height, s_Format, GL_UNSIGNED_BYTE, pBuffer);
glReadBuffer(lastBuffer);

// reset value of alpha channel with 255. because sometimes the value is 0, such as CS1.6
CWindowTool::ResetAlpha(pBuffer, len, 255); // this function should be completed by yourself

nWidth = width;
nHeight = height;
nPitch = pitch;
*pData = pBuffer;

return true;
}