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(S)VGA: Implement odd pel shifts in 256-color modes.

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This commit is contained in:
OBattler
2025-09-09 20:11:59 +02:00
parent bd5d058f76
commit 51c2328949
3 changed files with 30 additions and 5 deletions
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1
src/include/86box/vid_svga.h
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@@ -141,6 +141,7 @@ typedef struct svga_t {
int render_line_offset;
int start_retrace_latch;
int vga_mode;
int half_pixel;
/*The three variables below allow us to implement memory maps like that seen on a 1MB Trio64 :
0MB-1MB - VRAM

9
src/video/vid_svga.c
View File

@@ -1480,6 +1480,7 @@ svga_poll(void *priv)
svga->scanline = 0;
if (svga->attrregs[0x10] & 0x20) {
svga->scrollcache = 0;
svga->half_pixel = 0;
svga->x_add = svga->left_overscan;
}
}
@@ -1580,11 +1581,15 @@ svga_poll(void *priv)
if (svga->scrollcache > 8)
svga->scrollcache = 0;
}
svga->half_pixel = 0;
} else if ((svga->render == svga_render_2bpp_lowres) || (svga->render == svga_render_2bpp_highres) ||
(svga->render == svga_render_4bpp_lowres) || (svga->render == svga_render_4bpp_highres))
(svga->render == svga_render_4bpp_lowres) || (svga->render == svga_render_4bpp_highres)) {
svga->half_pixel = 0;
svga->scrollcache &= 0x07;
else
} else {
svga->half_pixel = svga->scrollcache & 0x01;
svga->scrollcache = (svga->scrollcache & 0x06) >> 1;
}
if ((svga->seqregs[1] & 8) || (svga->render == svga_render_8bpp_lowres))
svga->scrollcache <<= 1;

25
src/video/vid_svga_render.c
View File

@@ -805,6 +805,8 @@ svga_render_indexed_gfx(svga_t *svga, bool highres, bool combine8bits)
uint32_t incr_counter = 0;
uint32_t load_counter = 0;
uint32_t edat = 0;
uint32_t col = 0;
uint32_t col2 = 0;
for (x = 0; x <= (svga->hdisp + svga->scrollcache); x += charwidth) {
if (load_counter == 0) {
/* Find our address */
@@ -923,8 +925,19 @@ svga_render_indexed_gfx(svga_t *svga, bool highres, bool combine8bits)
}
} else if (combine8bits) {
if (svga->packed_4bpp) {
uint32_t p0 = svga->map8[c0 & svga->dac_mask];
uint32_t p1 = svga->map8[c1 & svga->dac_mask];
uint32_t p0;
uint32_t p1;
if (svga->half_pixel) {
col |= (c0 >> 4) & 0xff;
col2 = (c0 << 4) & 0xff;
col2 |= (c1 >> 4) & 0xff;
p0 = svga->map8[col & svga->dac_mask];
p1 = svga->map8[col2 & svga->dac_mask];
col = (c1 << 4) & 0xff;
} else {
p0 = svga->map8[c0 & svga->dac_mask];
p1 = svga->map8[c1 & svga->dac_mask];
}
const int outoffs = i << dwshift;
for (int subx = 0; subx < dotwidth; subx++)
p[outoffs + subx] = p0;
@@ -932,7 +945,13 @@ svga_render_indexed_gfx(svga_t *svga, bool highres, bool combine8bits)
p[outoffs + subx + dotwidth] = p1;
} else {
uint32_t ccombined = (c0 << 4) | c1;
uint32_t p0 = svga->map8[ccombined & svga->dac_mask];
uint32_t p0;
if (svga->half_pixel) {
col |= (ccombined >> 4) & 0xff;
p0 = svga->map8[col & svga->dac_mask];
col = (ccombined << 4) & 0xff;
} else
p0 = svga->map8[ccombined & svga->dac_mask];
const int outoffs = (i >> 1) << dwshift;
for (int subx = 0; subx < dotwidth; subx++)
p[outoffs + subx] = p0;