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Implement 4bpp graphics mode blink properly on VGA

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Closes #3447
This commit is contained in:
GreaseMonkey
2023-11-23 13:12:09 +13:00
parent 7de7ea3fe1
commit c8c9fa2f91
1 changed files with 18 additions and 6 deletions
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24
src/video/vid_svga_render.c
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@@ -486,7 +486,7 @@ svga_render_indexed_gfx(svga_t *svga, bool highres, bool combine8bits)
const int dwshift = highres ? 0 : 1;
const int dotwidth = 1 << dwshift;
const int charwidth = dotwidth * (combine8bits ? 4 : 8);
const uint8_t blinkmask = (attrblink ? 0x7 : 0xF);
const uint8_t blinkmask = (attrblink ? 0x8 : 0x0);
const uint8_t blinkval = (attrblink && blinked ? 0x8 : 0x0);
if ((svga->displine + svga->y_add) < 0)
@@ -594,12 +594,24 @@ svga_render_indexed_gfx(svga_t *svga, bool highres, bool combine8bits)
| (edatlookup[(edat[2] >> inshift) & 3][(edat[3] >> inshift) & 3] << 2);
// FIXME: Confirm blink behaviour on real hardware
// This is how it behaves on an Intel GMA 4500MHD (2008).
// That includes 8bpp modes.
// However, an AMD Stoney Ridge (2016) seems to ignore blink in 8bpp modes.
uint32_t c0 = ((dat >> 4) & svga->plane_mask & blinkmask) | blinkval;
uint32_t c1 = (dat & svga->plane_mask & blinkmask) | blinkval;
// The VGA 4bpp graphics blink logic was a pain to work out.
//
// If plane 3 is enabled in the attribute controller, then:
// - if bit 3 is 0, then we force the output of it to be 1.
// - if bit 3 is 1, then the output blinks.
// This can be tested with Lotus 1-2-3 release 2.3 with the WYSIWYG addon.
//
// If plane 3 is disabled in the attribute controller, then the output blinks.
// This can be tested with QBASIC SCREEN 10 - anything using color #2 should blink and nothing else.
//
// If you can simplify the following and have it still work, give yourself a medal.
//
uint32_t c0 = (dat >> 4) & 0xF;
uint32_t c1 = dat & 0xF;
c0 = ((c0 & svga->plane_mask & ~blinkmask) | ((c0 | ~svga->plane_mask) & blinkmask & blinkval)) ^ blinkmask;
c1 = ((c1 & svga->plane_mask & ~blinkmask) | ((c1 | ~svga->plane_mask) & blinkmask & blinkval)) ^ blinkmask;
if (combine8bits) {
uint32_t ccombined = (c0 << 4) | c1;
uint32_t p0 = svga->map8[ccombined];