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Implement special case of vertical blanking register 'usage'. Fixes Threat v1.40.

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Thanks ripsaw8080 for reporting.

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@3661
This commit is contained in:
Ralf Grillenberger 2010-11-10 19:58:10 +00:00
parent c493a07791
commit 15f221d8a1
1 changed files with 11 additions and 6 deletions
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17
src/hardware/vga_draw.cpp
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@ -1092,7 +1092,6 @@ void VGA_SetupDrawing(Bitu /*val*/) {
vtotal += 2;
hdend += 1;
vdend += 1;
vbstart += 1;
hbend = hbstart + ((hbend - hbstart) & 0x3F);
hrend = vga.crtc.end_horizontal_retrace & 0x1f;
@ -1107,10 +1106,16 @@ void VGA_SetupDrawing(Bitu /*val*/) {
if ( !vrend) vrend = vrstart + 0xf + 1;
else vrend = vrstart + vrend;
vbend = (vbend - vbstart) & 0x7f;
if ( !vbend) vbend = vbstart + 0x7f + 1;
else vbend = vbstart + vbend;
// Special case vbstart==0:
// Most graphics cards agree that lines zero to vbend are
// blanked. ET4000 doesn't blank at all if vbstart==vbend.
// ET3000 blanks lines 1 to vbend (255/6 lines).
if (vbstart != 0) {
vbstart += 1;
vbend = (vbend - vbstart) & 0x7f;
if ( !vbend) vbend = vbstart + 0x7f + 1;
else vbend = vbstart + vbend;
}
vbend++;
if (svga.get_clock) {
@ -1219,7 +1224,7 @@ void VGA_SetupDrawing(Bitu /*val*/) {
vdend = vbstart;
}
LOG(LOG_VGA,LOG_WARN)("Blanking wrap to line %d", vblank_skip);
} else if (vbstart==1) {
} else if (vbstart<=1) {
// blanking is used to cut lines at the start of the screen
vblank_skip = vbend;
LOG(LOG_VGA,LOG_WARN)("Upper %d lines of the screen blanked", vblank_skip);