Porting Pixel Operations

When porting code that involves pixel operations, keep the following points in mind:

Logical pixel operations are not applied to RGBA color buffers. For more information, see glLogicOp.
In general, IRIS GL uses the format ABGR for pixels, whereas OpenGL uses RGBA. You can change the format with glPixelStore.
When porting lrectwrite functions, be careful to note where lrectwrite is writing (for example, it could be writing to the depth buffer).

OpenGL gives you some additional flexibility in pixel operations. The following table lists IRIS GL functions for pixel operations and their equivalent OpenGL functions.

IRIS GL Function	OpenGL Function	Meaning
lrectread, rectread, readRGB	glReadPixels	Read a block of pixels from the frame buffer.
lrectwrite, rectwrite	glDrawPixels	Write a block of pixels to the frame buffer.
rectcopy	glCopyPixels	Copy pixels in the frame buffer.
rectzoom	glPixelZoom	Specify pixel zoom factors for glDrawPixels and glCopyPixels.
cmov	glRasterPos	Specify raster position for pixel operations.
readsource	glReadBuffer	Select a color buffer source for pixels.
pixmode	glPixelStore, glPixelTransfer	Set pixel storage modes. Set pixel transfer modes.
logicop	glLogicOp	Specify a logical operation for pixel writes.
—	glEnable(GL_LOGIC_OP)	Turn on pixel logic operations.

For a complete list of possible logical operations, see glLogicOp.

This IRIS GL code sample shows a typical pixel write:

unsigned long *packedRaster; 
.. 
packedRaster[k] = 0x00000000; 
.. 
lrectwrite(0, 0, xSize, ySize, packedRaster);

The preceding code looks like this when translated to OpenGL:

glRasterPos2i( 0, 0); 
glDrawPixels( xSize + 1, ySize + 1, GL_RGBA, GL_UNSIGNED_BYTE,
              packedRaster);