What can prevent OpenGL glDrawPixels from working on some video cards?

Question

The following code does not write data to the rear buffer of Intel integrated video cards, for example, on a MacBook. On ATI cards, such as the iMac, it accesses the back buffer. The width and height are correct (and the buffer is 800x600), and the m_PixelBuffer is correctly filled with 0xAA00AA00.

My best guess is that there is something amiss with the need to install glWindowPos. I do not currently set it (or raster position), and when I get GL_CURRENT_RASTER_POSITION, I noticed that the default value on the ATI card is 0,0,0,0, and Intel - 0,0,0,1. When I set the raster pose on the ATI card to 0,0,0,1, I get the same result as the Intel card, nothing accesses the feedback buffer. Is there some kind of transformation state that I am missing? This is a 2D application, so view conversion is very simple glOrtho.

glDrawPixels(GetBufferWidth(), GetBufferHeight(), GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, m_PixelBuffer);

For more information I can provide, please ask. I'm pretty much OpenGL and Mac newb, so I don't know if I am providing enough information.

Answer 1

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Answer 2

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Answer 3

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Answer 4

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glDrawPixels()

GLint valid;
glGet(GL_CURRENT_RASTER_POSITION_VALID, &valid);

This should tell you if the current raster position is valid. If so, then this is not your problem.