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Old 27 June 2013, 22:25   #50
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Originally Posted by kovacm View Post
and than, it is interesting that Amiga coders did not use this trick until... ???
The first Amiga coders to use this "trick" were the programmers responsible for writing the operating system before the Amiga was even released.

Intuition, the windowing system of the Amiga, allows an application to open up its own screen with certain attributes, like resolution, number of colors, color palette, width, height, etc. But the Amiga is also a multitasking operating system, so there may be several programs running at the same time with different screen requirements.

Intuition uses the COPPER to allow several applications running simultaneously to share the same display by changing the color palette, the frame buffer address, even the resolution, mid-screen. The top half of the display might show a 320x100 32 color screen, for example, while the bottom half shows a 640x300 16 color screen.

It's an old trick made efficient by the COPPER and used in the Amiga from the start.

Originally Posted by kovacm View Post
I bet that PCHG pictures looks better than HAM

Suppose that it does? There's very little CPU time left for anything else.

With HAM, 70% of the CPU time remains for things like decompressing a HAM animation. How many animated Photochrome images have you seen? And DMA is still available for audio, blitter, copper, sprites, and disk.

But if a programmer really wanted to he could page flip and use the COPPER to alter the 16 palette registers of a HAM image mid-scanline to improve it further. I think during HAM display the COPPER can perform 35 arbitrary writes to the 16 color palette available in HAM.
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