S3 XGA: Add support for accelerated 4bpp 16-color packed SVGA modes, …

…which fixes display problems with ORCAD S3 support
joncampbell123 · Jul 9, 2024 · b095cf2 · b095cf2
1 parent 61aa6a6
commit b095cf2
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Showing 3 changed files with 47 additions and 18 deletions.
diff --git a/CHANGELOG b/CHANGELOG
@@ -1,4 +1,8 @@
 NEXT
+  - S3 XGA emulation: Add XGA acceleration for 4bpp packed 16-color
+    SVGA modes. A CAD package has S3 support drivers that use the
+    16-color 4bpp packed modes and expects XGA acceleration to work.
+    (joncampbell123).
   - Add "-o int13" option to IMGMOUNT to direct the FAT driver to do
     all disk I/O through INT 13h instead of directly. This is intended
     for certain demoscene productions that apparently like to make

diff --git a/src/hardware/vga_s3.cpp b/src/hardware/vga_s3.cpp
@@ -35,6 +35,18 @@ extern bool enable_pci_vga;
 extern unsigned int vbe_window_granularity;
 extern unsigned int vbe_window_size;
 
+void S3_UpdateXGAColorMode(void) {
+	switch (vga.s3.reg_50 & S3_XGA_CMASK) {
+		case S3_XGA_32BPP: vga.s3.xga_color_mode = M_LIN32; break;
+		case S3_XGA_16BPP: vga.s3.xga_color_mode = M_LIN16; break;
+		case S3_XGA_8BPP:
+			/* FIXME: 4/8bpp packed is controlled by the advanced function control register (0x4AE8) bit 2 which is not yet emulated here */
+			vga.s3.xga_color_mode = M_LIN8;
+			if ((vga.s3.misc_control_2 >> 4) == 0xF/*hacked 4bpp*/) vga.s3.xga_color_mode = M_LIN4;
+			break;
+	}
+}
+
 void SVGA_S3_WriteCRTC(Bitu reg,Bitu val,Bitu iolen) {
     (void)iolen;//UNUSED
     switch (reg) {
@@ -170,11 +182,7 @@ void SVGA_S3_WriteCRTC(Bitu reg,Bitu val,Bitu iolen) {
         break;
     case 0x50:  // Extended System Control 1
         vga.s3.reg_50 = (uint8_t)val;
-        switch (val & S3_XGA_CMASK) {
-            case S3_XGA_32BPP: vga.s3.xga_color_mode = M_LIN32; break;
-            case S3_XGA_16BPP: vga.s3.xga_color_mode = M_LIN16; break;
-            case S3_XGA_8BPP: vga.s3.xga_color_mode = M_LIN8; break;
-        }
+        S3_UpdateXGAColorMode();
         switch (val & S3_XGA_WMASK) {
             case S3_XGA_1024: vga.s3.xga_screen_width = 1024; break;
             case S3_XGA_1152: vga.s3.xga_screen_width = 1152; break;
@@ -399,6 +407,7 @@ void SVGA_S3_WriteCRTC(Bitu reg,Bitu val,Bitu iolen) {
                     13  (732/764) 32bit (1 pixel/VCLK)
         */
         vga.s3.misc_control_2=(uint8_t)val;
+        S3_UpdateXGAColorMode();
         VGA_DetermineMode();
         break;
     case 0x69:  /* Extended System Control 3 */

diff --git a/src/hardware/vga_xga.cpp b/src/hardware/vga_xga.cpp
@@ -355,6 +355,13 @@ void XGA_DrawPoint(Bitu x, Bitu y, Bitu c) {
 	   one is actually 24-bit. Without this step there may be some graphics corruption (mainly,
 	   during windows dragging. */
 	switch(XGA_COLOR_MODE) {
+		case M_LIN4:
+			{
+				uint8_t shf = ((memaddr^1u)&1u)*4u;
+				if (GCC_UNLIKELY((memaddr/2) >= vga.mem.memsize)) break;
+				vga.mem.linear[memaddr/2] = (vga.mem.linear[memaddr/2] & (0xF0 >> shf)) + ((c&0xF) << shf);
+			}
+			break;
 		case M_LIN8:
 			if (GCC_UNLIKELY(memaddr >= vga.mem.memsize)) break;
 			vga.mem.linear[memaddr] = (uint8_t)c;
@@ -374,11 +381,12 @@ void XGA_DrawPoint(Bitu x, Bitu y, Bitu c) {
 		default:
 			break;
 	}
-
 }
 
 Bitu XGA_PointMask() {
 	switch(XGA_COLOR_MODE) {
+		case M_LIN4:
+			return 0xFul;
 		case M_LIN8:
 			return 0xFFul;
 		case M_LIN15:
@@ -396,19 +404,23 @@ Bitu XGA_GetPoint(Bitu x, Bitu y) {
 	uint32_t memaddr = (uint32_t)((y * XGA_SCREEN_WIDTH) + x);
 
 	switch(XGA_COLOR_MODE) {
-	case M_LIN8:
-		if (GCC_UNLIKELY(memaddr >= vga.mem.memsize)) break;
-		return vga.mem.linear[memaddr];
-	case M_LIN15:
-	case M_LIN16:
-		if (GCC_UNLIKELY(memaddr*2 >= vga.mem.memsize)) break;
-		return ((uint16_t*)(vga.mem.linear))[memaddr];
-	case M_LIN32:
-		if (GCC_UNLIKELY(memaddr*4 >= vga.mem.memsize)) break;
-		return ((uint32_t*)(vga.mem.linear))[memaddr];
-	default:
-		break;
+		case M_LIN4:
+			if (GCC_UNLIKELY((memaddr/2) >= vga.mem.memsize)) break;
+			return (vga.mem.linear[memaddr/2] >> (((memaddr&1)^1)*4)) & 0xF;
+		case M_LIN8:
+			if (GCC_UNLIKELY(memaddr >= vga.mem.memsize)) break;
+			return vga.mem.linear[memaddr];
+		case M_LIN15:
+		case M_LIN16:
+			if (GCC_UNLIKELY(memaddr*2 >= vga.mem.memsize)) break;
+			return ((uint16_t*)(vga.mem.linear))[memaddr];
+		case M_LIN32:
+			if (GCC_UNLIKELY(memaddr*4 >= vga.mem.memsize)) break;
+			return ((uint32_t*)(vga.mem.linear))[memaddr];
+		default:
+			break;
 	}
+
 	return 0;
 }
 
@@ -1420,6 +1432,8 @@ void XGA_DrawCmd(Bitu val, Bitu len) {
 
 void XGA_SetDualReg(uint32_t& reg, Bitu val) {
 	switch(XGA_COLOR_MODE) {
+	case M_LIN4:
+		reg = (uint8_t)(val&0xf); break;
 	case M_LIN8:
 		reg = (uint8_t)(val&0xff); break;
 	case M_LIN15:
@@ -1441,6 +1455,8 @@ void XGA_SetDualReg(uint32_t& reg, Bitu val) {
 
 Bitu XGA_GetDualReg(uint32_t reg) {
 	switch(XGA_COLOR_MODE) {
+	case M_LIN4:
+		return (uint8_t)(reg&0xf);
 	case M_LIN8:
 		return (uint8_t)(reg&0xff);
 	case M_LIN15: case M_LIN16: