rrrreeeeaaaaddddssssoooouuuurrrrcccceeee specifies the pixel source buffer that rrrreeeeccccttttccccooooppppyyyy, rrrreeeeaaaaddddppppiiiixxxxeeeellllssss,
rrrreeeeaaaaddddRRRRGGGGBBBB, rrrreeeeccccttttrrrreeeeaaaadddd, and llllrrrreeeeccccttttrrrreeeeaaaadddd use. A separate read source is
maintained for each of the GL framebuffers: normal, pop-up, overlay, and
underlay. Calls to rrrreeeeaaaaddddssssoooouuuurrrrcccceeee change the read source of the currently
active framebuffer, as specified by ddddrrrraaaawwwwmmmmooooddddeeee. By default the read source
for each framebuffer is SSSSRRRRCCCC____AAAAUUUUTTTTOOOO.
Because read sources, with the exception of some implemented only on the
Personal Iris, always specify a source within the current framebuffer, it
is not possible to copy pixels from one framebuffer to another. Such a
copy must be implemented by first reading pixels out of the source
framebuffer, then changing the draw mode to the destination framebuffer,
and writing the pixels.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
lrectread, readpixels, readRGB, rectcopy
NNNNOOOOTTTTEEEESSSS
This subroutine is available only in immediate mode.
On the IRIS-4D B or G models, SSSSRRRRCCCC____ZZZZBBBBUUUUFFFFFFFFEEEERRRR is not available.
Read sources SSSSRRRRCCCC____OOOOVVVVEEEERRRR, SSSSRRRRCCCC____UUUUNNNNDDDDEEEERRRR, and SSSSRRRRCCCC____PPPPUUUUPPPP operate only on the
Personal Iris.
BBBBUUUUGGGGSSSS
On the IRIS-4D GT and GTX models, and on all Personal IRIS, XS, XS24, XZ,
Elan and Extreme systems, a single rrrreeeeaaaaddddssssoooouuuurrrrcccceeee variable is shared between
the four framebuffers.
On the Personal Iris, the source for pixel reads does not change when
changing framebuffers (via ddddrrrraaaawwwwmmmmooooddddeeee) unless the current selected read
source is SSSSRRRRCCCC____AAAAUUUUTTTTOOOO (the default).
On some IRIS-4D GT and GTX models, while copying rectangles with blending
active, rrrreeeeaaaaddddssssoooouuuurrrrcccceeee also specifies the bank from which _d_e_s_t_i_n_a_t_i_o_n color
and alpha are read (overriding the bbbblllleeeennnnddddffffuuuunnnnccccttttiiiioooonnnn setting).