asynchronous readback

asyncreadback.cpp

void setup()
{
	pboIds = new GLuint[2];
	pboIds[0] = 0; pboIds[1] = 0;
	const int DATA_SIZE = screenWidth * screenHeight * 4;
	const int PBO_COUNT = 2;
	glGenBuffersARB(PBO_COUNT, pboIds);
	glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);
	glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);
	glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[1]);
	glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);
	glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);
}

void draw() 
{
	// draw a bunch of stuff
	// 
	//

	if (bSaveMovie) {
        // Asynchronous readback
        glReadBuffer(GL_BACK);
        
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);
        glReadPixels(0, 0, screenWidth, screenHeight, GL_BGRA, GL_UNSIGNED_BYTE, 0);
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);
        
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[1]);
        glReadPixels(0, 0, screenWidth, screenHeight, GL_BGRA, GL_UNSIGNED_BYTE, 0);
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);
        
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);
        GLubyte* src = (GLubyte*)glMapBufferARB(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);
        
        int y_offset = 0;//screenHeight - videoHeight;
        int x_offset = 0;//videoWidth;
        
        // save movie // RGB <- BGRA
        if(src)
        {	
            for (int y = 0; y < screenHeight; y++)	
            {
                for (int x = 0; x < screenWidth; x++)	
                {
                    int idx = (x+y*(screenWidth))*3;
                    int idx2 = 4*(x+x_offset)+4*(screenHeight-y-1+y_offset)*screenWidth;
                    readBackFrame[idx+0] = src[idx2+2];		
                    readBackFrame[idx+1] = src[idx2+1];				
                    readBackFrame[idx+2] = src[idx2+0];						
                }
            }		
            
            if (bSaveImages) 
            {
                ofImage img;
                img.setFromPixels(readBackFrame, screenWidth, screenHeight, OF_IMAGE_COLOR, true);
                char buf[256];
                sprintf(buf, "frame_%08d.jpg", currentFrame);
                img.saveImage(ofToDataPath(buf), OF_IMAGE_QUALITY_BEST);
            }
            
            videoSaver.addFrame(readBackFrame, 1.0f / fps); 
        }
        
        glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_ARB);     // release pointer to the mapped buffer	
        glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);	
    }
}