English Amiga Board - View Single Post - Dodgy Icons Graphics In AmigaOS 3.9 (Under AGA)

thomas · 23 July 2016, 10:18

Moving gfx data around on an RTG gfx card has to be done by the CPU anyway, therefore P96 allocates bitmaps in Fast RAM for speed. In Prefs/Workbench you can tell WB to do the same.

However, if you open a native screen, the screen's bitmap must reside in Chip RAM because the Amiga native gfx chips can only access Chip RAM. And moving around bitmaps in Chip RAM is fastest done by the Amiga blitter which can access only Chip RAM, too.

Now there is a conflict if a custom bitmap (not allocated by AllocBitMap) is located in Fast RAM but should be copied to the native display. If you try to do this with the blitter it will copy some random Chip RAM instead of the Fast RAM where the bitmap is located.

Therefore you have to disable the Amiga blitter and use the CPU to copy bitmaps if the bitmaps reside in Fast RAM and the display is in Chip RAM.

23 July 2016, 10:18	#9
thomas Registered User Join Date: Jan 2002 Location: Germany Posts: 7,021	Moving gfx data around on an RTG gfx card has to be done by the CPU anyway, therefore P96 allocates bitmaps in Fast RAM for speed. In Prefs/Workbench you can tell WB to do the same. However, if you open a native screen, the screen's bitmap must reside in Chip RAM because the Amiga native gfx chips can only access Chip RAM. And moving around bitmaps in Chip RAM is fastest done by the Amiga blitter which can access only Chip RAM, too. Now there is a conflict if a custom bitmap (not allocated by AllocBitMap) is located in Fast RAM but should be copied to the native display. If you try to do this with the blitter it will copy some random Chip RAM instead of the Fast RAM where the bitmap is located. Therefore you have to disable the Amiga blitter and use the CPU to copy bitmaps if the bitmaps reside in Fast RAM and the display is in Chip RAM.