On Monday 11 December 2000 14:28, you wrote:
> This effect of interlacing is already implemented in brmsx since
> version 2.6. It's used in the game Breaker. Instead of making a more
> complex vram retrieve, like you're doing, I opted for a complete shuffling
> of all the 128kb of vram each time you switch from a lower screen to a
> screen greater than 6. This should be a bit slower in games that change
> screen 5/7 in line interrupts, but it's much faster in the general case (I
> always optimize for the general case).
I implemented that approach about a year ago, but Marat rejected it.
The first reason is the one you mention: the reshufle takes a lot of time and
if it's executed often (line interrupts) it will slow down the emulation a
lot. However, I don't know of any existing program that changes between
SCREEN7/8 and a lower screen mode on a line interrupt.
The second reason is that my implementation required a 128K auxiliary array.
I know a way to implement it using a 64K auxiliary array. But I'm curious if
it can be done with significantly less auxiliary memory. Well, ofcourse any
permutation can be written as a series of swaps, but that may be a lot slower
compared to the auxiliary array approach.
> Check out the implementation in the brmsx source code,
> file V9938.ASM, routines vram_interlace and vram_deinterlace.
Why do you call this "interlace"?
Anyway, these are the routines I used:
fprintf(stderr, "Reordering to 7/8...\n");
Src0 = VRAM;
Src1 = VRAM + (1<<16);
Dst = VRAM_ALT;
for (Count = 1<<16; Count; Count--) {
*Dst++ = *Src0++;
*Dst++ = *Src1++;
}
fprintf(stderr, "Reordering from 7/8...\n");
Src = VRAM;
Dst0 = VRAM_ALT;
Dst1 = VRAM_ALT + (1<<16);
for (Count = 1<<16; Count; Count--) {
*Dst0++ = *Src++;
*Dst1++ = *Src++;
}
Bye,
Maarten
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