The Windows 95 S3 driver 16-color modes are not planar, but packed. U…

…pdate VESA modelist. This fixes garbled display in Windows 95 for 800x600, 1024x768, and 1280x1024 16-color display modes. Noted: Windows 98 and higher refuse to support 16-color modes other than stock VGA 640x480 16-color planar.

CHANGELOG

@@ -1,4 +1,13 @@
 Next:
+  - Windows 95 S3 driver behavior suggests that S3 16-color VESA modes
+    0x202 to 0x208 are NOT planar modes, but packed modes. Change modes to
+    M_PACKED4 and update modelist building to allow that range even if the
+    dosbox.conf is configured not to list 4bpp packed VESA modes. This fixes
+    Windows 95 S3 driver 16-color modes 800x600, 1024x768, 1280x1024.
+    Noted: Windows 95 is the last version of Windows to support 4bpp packed.
+           Windows 98 and higher refuses to support it and the Display settings
+           will not allow you to select any 16-color mode other than the stock
+           VGA 640x480 16-color planar mode. (joncampbell123)
   - Add --load-seg option to BOOT in case any PC-98 game boot floppy expects
     to be loaded somewhere other than the default. PC-98 game "Private School
     Adventure" will crash if loaded to segment 0x1FC0 but runs fine if booted

src/ints/int10_modes.cpp

@@ -209,14 +209,25 @@ VideoModeBlock ModeList_VGA[]={
 { 0x192  ,M_LIN32  ,320 ,480 ,40 ,60 ,8 ,8  ,1 ,0xA0000 ,0x10000, 50 ,525 ,40 ,480 ,_UNUSUAL_MODE },
 
 // S3 specific modes (OEM modes). See also [http://www.ctyme.com/intr/rb-0275.htm]
+// NTS: The 4bpp modes are PACKED not PLANAR. The Windows 95 S3 driver expects the 4bpp modes to provide
+//      a PACKED structure and M_LIN4 will result in an incorrect display. It is impossible to test these
+//      with Windows 98 and higher because the Display settings in Windows 98 REFUSES to let you select
+//      any 16-color mode other than 640x480 even if the driver allows it (this was also when Microsoft
+//      made it impossible to select monochrome display modes that Windows 95 once allowed i.e. 640x400
+//      monochrome 2-color mode).
+//
+//      These modes are needed for the Windows 95 driver and are provided regardless of the dosbox.conf
+//      "allow 4bpp packed vesa modes" option.
+//
+// FIXME: These don't work with the S3 Windows 3.1 drivers though.
 { 0x201  ,M_LIN8	,640 ,480, 80,30 ,8 ,16 ,1 ,0xA0000 ,0x10000,100 ,525 ,80 ,480 , _VGA_PIXEL_DOUBLE },
-{ 0x202  ,M_LIN4	,800 ,600,100,37 ,8 ,16 ,1 ,0xA0000 ,0x10000,132 ,628 ,100,600 ,0	},
+{ 0x202  ,M_PACKED4	,800 ,600,100,37 ,8 ,16 ,1 ,0xA0000 ,0x10000,132 ,628 ,100,600 ,0	},
 { 0x203  ,M_LIN8	,800 ,600,100,37 ,8 ,16 ,1 ,0xA0000 ,0x10000,132 ,628 ,100,600 ,0	}, // Line Wars II, S3 accelerated 800x600
-{ 0x204  ,M_LIN4	,1024,768,128,48 ,8 ,16 ,1 ,0xA0000 ,0x10000,168 ,806 ,128,768 ,0	},
+{ 0x204  ,M_PACKED4	,1024,768,128,48 ,8 ,16 ,1 ,0xA0000 ,0x10000,168 ,806 ,128,768 ,0	},
 { 0x205  ,M_LIN8	,1024,768,128,48 ,8 ,16 ,1 ,0xA0000 ,0x10000,168 ,806 ,128,768 ,0	},
-{ 0x206  ,M_LIN4	,1280,960,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,212 ,1024,160,960 ,0	}, // TODO VERIFY THIS
+{ 0x206  ,M_PACKED4	,1280,960,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,212 ,1024,160,960 ,0	}, // TODO VERIFY THIS
 { 0x207  ,M_LIN8	,1152,864,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,182 ,948 ,144,864 ,0	},
-{ 0x208  ,M_LIN4	,1280,1024,160,64,8 ,16 ,1 ,0xA0000 ,0x10000,212 ,1066,160,1024,0	},
+{ 0x208  ,M_PACKED4	,1280,1024,160,64,8 ,16 ,1 ,0xA0000 ,0x10000,212 ,1066,160,1024,0	},
 { 0x209  ,M_LIN15	,1152,864,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,364 ,948 ,288,864 ,0	},
 { 0x20A  ,M_LIN16	,1152,864,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,364 ,948 ,288,864 ,0	},
 { 0x20B  ,M_LIN32	,1152,864,160,64 ,8 ,16 ,1 ,0xA0000 ,0x10000,182 ,948 ,144,864 ,0	},
@@ -2292,7 +2303,7 @@ Bitu VideoModeMemSize(Bitu mode) {
 
 	switch(vmodeBlock->type) {
     case M_PACKED4:
-		if (mode >= 0x100 && !allow_vesa_4bpp_packed) return ~0ul;
+		if (mode >= 0x100 && !(mode >= 0x202 && mode <= 0x208)/*S3 Windows 95 driver needs these*/ && !allow_vesa_4bpp_packed) return ~0ul;
 		return vmodeBlock->swidth*vmodeBlock->sheight/2;
 	case M_LIN4:
 		if (mode >= 0x100 && !allow_vesa_4bpp) return ~0ul;

src/ints/int10_vesa.cpp

@@ -294,7 +294,7 @@ uint8_t VESA_GetSVGAModeInformation(uint16_t mode,uint16_t seg,uint16_t off) {
 
 	switch (mblock->type) {
 	case M_PACKED4:
-		if (!allow_vesa_4bpp_packed) return VESA_FAIL;//TODO: New option to disable
+		if (!allow_vesa_4bpp_packed && !(ModeList_VGA[i].mode >= 0x202 && ModeList_VGA[i].mode <= 0x208)) return VESA_FAIL;//TODO: New option to disable
 		pageSize = mblock->sheight * mblock->swidth/2;
 		var_write(&minfo.BytesPerScanLine,(uint16_t)((((mblock->swidth+15U)/8U)&(~1U))*4)); /* NTS: 4bpp requires even value due to VGA registers, round up */
 		if (!int10.vesa_oldvbe10) { /* optional in VBE 1.0 */
@@ -904,6 +904,7 @@ Bitu INT10_WriteVESAModeList(Bitu max_modes) {
                         (ModeList_VGA[i].special & _USER_MODIFIED) ||
                         (ModeList_VGA[i].swidth <= SCALER_MAXWIDTH && ModeList_VGA[i].sheight <= SCALER_MAXHEIGHT);
                     bool allow_res = allow1 && allow2 && allow3 && allow4 && allow5;
+		    bool allow_s3_packed4 = (ModeList_VGA[i].mode >= 0x202 && ModeList_VGA[i].mode <= 0x208);
 
                     switch (ModeList_VGA[i].type) {
                         case M_LIN32:	canuse_mode=allow_vesa_32bpp && allow_res; break;
@@ -912,7 +913,7 @@ Bitu INT10_WriteVESAModeList(Bitu max_modes) {
                         case M_LIN15:	canuse_mode=allow_vesa_15bpp && allow_res; break;
                         case M_LIN8:	canuse_mode=allow_vesa_8bpp && allow_res; break;
                         case M_LIN4:	canuse_mode=allow_vesa_4bpp && allow_res; break;
-                        case M_PACKED4:	canuse_mode=allow_vesa_4bpp_packed && allow_res; break;
+                        case M_PACKED4:	canuse_mode=(allow_vesa_4bpp_packed || allow_s3_packed4) && allow_res; break;
                         case M_TEXT:	canuse_mode=allow_vesa_tty && allow_res; break;
                         default:	break;
                     }