pbo

I want to use two PBOs to read pixel in alternative way. I thought the PBO way will much faster, because glReadPixels returns immediately when using PBO, and a lot of time can be overlapped. Strangely there seems to be not much benefit. Considering some code like: glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0); Timer t; t.start(); glReadPixels(0,0,1024,1024,GL_RGBA, GL_UNSIGNED_BYTE, buf); t.stop(); std::cout << t.getElapsedTimeInMilliSec() << " "; glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pbo); t.start(); glReadPixels(0,0,1024,1024,GL_RGBA, GL_UNSIGNED_BYTE, 0); t.stop(); std::cout << t

Can I use Pixel Buffer Object (PBO) to directly read the pixels values (i.e. using glReadPixels) from the FBO (i.e. while FBO is still attached)? If yes, What are the advantages and disadvantages of using PBO with FBO? What is the problem with following code { //DATA_SIZE = WIDTH * HEIGHT * 3 (BECAUSE I AM USING 3 CHANNELS ONLY) // FBO and PBO status is good . . glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fboId); //Draw the objects Following glReadPixels works fine glReadPixels(0, 0, screenWidth, screenHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, (uchar*)cvimg->imageData); Following glReadPixels DOES

What are the disadvantages of always using alginment of 1? glPixelStorei(GL_UNPACK_ALIGNMENT, 1) glPixelStorei(GL_PACK_ALIGNMENT, 1) Will it impact performance on modern gpus? How can data not be 1-byte aligned? This strongly suggests a lack of understanding of what the row alignment in pixel transfer operations means . Image data that you pass to OpenGL is expected to be grouped into rows. Each row contains width number of pixels, with each pixel being the size as defined by the format and type parameters. So a format of GL_RGB with a type of GL_UNSIGNED_BYTE will result in a pixel that is 24