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S3 YUV: Use K1 and K2 vertical scalefactors as intended, which also works just as well with Windows

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This commit is contained in:
Jonathan Campbell
2021-04-12 19:47:38 -07:00
parent 39dd20e0ef
commit 88f66b484d
3 changed files with 13 additions and 17 deletions
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2
include/vga.h
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@@ -665,7 +665,7 @@ typedef struct {
// Set to: [height in lines of initial output window before scaling] - 1
// (MM81E4 K2 Vertical Scale Factor)
uint16_t k2_vscale_factor; // [10: 0] K2 Vertical Scale Factor
int16_t k2_vscale_factor; // [10: 0] K2 Vertical Scale Factor
// Set to: (height in lines before scale) - (height in lines of final window after scaling)
// (MM81E8 DDA Vertical Accumulator Initial Value)

26
src/hardware/vga_draw.cpp
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@@ -1050,27 +1050,21 @@ void S3_XGA_SecondaryStreamRender(uint32_t* temp2) {
S3_XGA_RenderYUY2(temp2+S3SSdraw.startx);
/* it's not clear from the datasheet, but I think what the card is doing is a
* DDA to vertically scale the image.
* DDA to vertically scale the image, and K1/K2 are just terms to add/subtract
* to vertically scale.
*
* FIXME: This works, but what is the K2 vertical scale factor for?
* What use could (height in lines of original - height in lines of final)
* be to the card? Filtering and interpolation?
* The code below seems to work well enough with Windows 3.1 and Windows 98.
* Note of course this algorithm doesn't allow scaling DOWN YUV playback.
*
* It's documented as the "initial accumulator" of the vertical scale
* DDA, but use of the value during scaling hardly counts as just the
* "initial accumulator".
* Note that K1 = original height - 1
* K2 = (original height) - (final height)
*
* Furthermore, S3 Trio64V+ documents it as "2's complement of..." while
* ViRGE documents it as just the subtraction in question.
*
* Also note: Windows 3.1 DCI drivers will set the vscale factors and accumulator
* all to zero if the vertical scale is 1:1, which also suggests
* vertical scaling is DDA behavior.
*
* This has been tested so far with Windows 3.1 and Windows 98. */
* NTS: Windows 3.1 DCI and Windows 98 DirectX drivers will set initial accumulator
* and both K1/K2 scale factors to zero if the vertical scale is 1:1. */
S3SSdraw.vaccum += vga.s3.streams.k1_vscale_factor;
if (S3SSdraw.vaccum >= 0) {
S3SSdraw.vaccum += vga.s3.streams.dda_vaccum_iv;
S3SSdraw.vaccum -= vga.s3.streams.k1_vscale_factor;
S3SSdraw.vaccum += vga.s3.streams.k2_vscale_factor;
S3SSdraw.vmem_addr += S3SSdraw.stride;
}
}

2
src/hardware/vga_xga.cpp
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@@ -1271,6 +1271,8 @@ void XGA_Write(Bitu port, Bitu val, Bitu len) {
case 0x81E4: // S3 Trio64V+ streams processor, K2 Vertical Scale Factor (MMIO only)
if (s3Card == S3_Trio64V || s3Card >= S3_ViRGE) {
vga.s3.streams.k2_vscale_factor = val & 0x7FFu;
if (vga.s3.streams.k2_vscale_factor & 0x400u)
vga.s3.streams.k2_vscale_factor -= 0x800u;
}
break;
case 0x81E8: // S3 Trio64V+ streams processor, DDA Vertical Accumulator Initial Value (MMIO only)