DOS FAT driver: When -o int 13 is in effect, automatically adjust dis…

…k geometry according to media byte so that DS_BLISS.EXE still works even if you initially image mounted a 1.44MB floppy image

CHANGELOG

@@ -1,4 +1,8 @@
 NEXT
+  - DOS FAT driver: If INT 13h reports disk change, adapt floppy
+    disk geometry to new disk image according to media byte. This
+    allows DS_BLISS to present it's 720K fake floppy even if the
+    user initially mounted a 1.44MB floppy to drive A: (joncampbell123).
   - INT 10 mode list: Add "pitch" parameter. If nonzero, the value
     (in pixels) is how to program the pixels per scanline when
     setting the mode.

src/dos/drive_fat.cpp

@@ -3678,7 +3678,7 @@ void fatDrive::checkDiskChange(void) {
 	 * existence by intercepting INT 13h for floppy I/O and then expecting MS-DOS to call INT 13h
 	 * to read it. Furthermore, at some parts of the demo, the INT 13h hook changes the root
 	 * directory and FAT table to make the next "disk" appear, even if the volume label does not. */
-	if (loadedDisk->detectDiskChange() && !BPB.is_fat32()) {
+	if (loadedDisk->detectDiskChange() && !BPB.is_fat32() && partSectOff == 0) {
 		LOG(LOG_MISC,LOG_DEBUG)("FAT: disk change");
 
 		FAT_BootSector bootbuffer = {};
@@ -3712,6 +3712,18 @@ void fatDrive::checkDiskChange(void) {
 			return;
 		}
 
+		/* sometimes as part of INT 13h interception the new image will differ from the format we mounted against (DS_BLISS.EXE) */
+		/* TODO: Add any other format here */
+		if (BPB.v.BPB_Media == 0xF9) {
+			LOG(LOG_MISC,LOG_DEBUG)("NEW FAT: changing floppy geometry to 720k format according to media byte");
+			loadedDisk->Set_Geometry(2/*heads*/,80/*cylinders*/,9/*sectors*/,512/*sector size*/);
+		}
+		else if (BPB.v.BPB_Media == 0xF0) {
+			/* TODO: By the time DOS supported the 1.44MB format the BPB also provided the geometry too */
+			LOG(LOG_MISC,LOG_DEBUG)("NEW FAT: changing floppy geometry to 1.44M format according to media byte");
+			loadedDisk->Set_Geometry(2/*heads*/,80/*cylinders*/,18/*sectors*/,512/*sector size*/);
+		}
+
 		uint32_t RootDirSectors;
 		uint32_t DataSectors;