PATH ADC Home > Documentation > Hardware > Device Managers and Drivers > PCI Card Services > Designing PCI Cards and Drivers for Power Macintosh Computers

GrayPage (csCode = 5)

The required GrayPage routine fills the specified video page with a dithered gray pattern in the current video mode. The page number is 0 based.



 
OSErr = Control(theDeviceRefNum, cscGrayPage, &theVDPageInfo );

-- csMode: Unused
-- csData: Unused
--> csPage: Desired display page to gray
-- csBaseAddr: Unused

The purpose of the GrayPage routine is to eliminate visual artifacts on the screen during mode changes. When the mode changes, the contents of the frame buffer immediately acquire a new color meaning. To avoid annoying color flashes, two events must occur:

SetMode or SwitchMode sets the entire contents of the CLUT to 50 percent gray before changing the mode, so that all possible indexes in either the old or new depth appear the same.
GrayPage fills the frame buffer with one of these 50 percent dither patterns:

0xAAAAAAAA represents 32 pixels at 1 bpp

0xCCCCCCCC represents 16 pixels at 2 bpp

0xF0F0F0F0 represents 8 pixels at 4 bpp

0xFF00FF00 represents 4 pixels at 8 bpp

0xFFFF0000 represents 2 pixels at 16 bpp

0xFFFFFFF represents 1 pixel at 32 bpp (invert to get the next pixel)

For direct devices, GrayPage also builds a three-channel linear gray color table, gamma-corrects the table, and loads it into the color table hardware.