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dos: Use INT 0x10/AX=0x1A00 to detect VGA presence

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palxex
2026-06-30 15:44:10 +08:00
committed by Ryan C. Gordon
parent ef6e76e00b
commit f09a6679a3
1 changed files with 7 additions and 10 deletions
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17
src/video/dos/SDL_dosmodes.c
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@@ -219,18 +219,15 @@ static const SDL_VESAInfo *GetVESAInfo(void)
return vesa_info;
}
// Test by writing and reading back the DAC Pixel Mask register
// On VGA this is a read/write register, on EGA/CGA the port either
// doesn't exist (reads 0xFF) or isn't writable.
// Check for VGA using BIOS function GET DISPLAY COMBINATION CODE.
// Call INT 0x10 with AX=0x1A00; function is supported if AL=0x1A.
// Returns true for VGA-compatible hardware.
static bool DetectVGA(void)
{
const Uint8 original = inportb(VGA_DAC_PIXEL_MASK);
outportb(VGA_DAC_PIXEL_MASK, 0xA5);
(void)inportb(0x80); // small I/O delay
const Uint8 readback = inportb(VGA_DAC_PIXEL_MASK);
outportb(VGA_DAC_PIXEL_MASK, original);
return (readback == 0xA5);
__dpmi_regs regs = {};
regs.x.ax = 0x1A00;
__dpmi_int(0x10, &regs);
return ((regs.x.ax & 0x00FF) == 0x001A);
}
bool DOSVESA_SupportsVESA(void)