Add 8-bit video mode for SDL2 and use it in DOS

There are still some glitches in screen transitions but that's probably
our fault. We can improve it later.

Author: glebm

3rdParty/SDL2/CMakeLists.txt

@@ -19,8 +19,8 @@ if(TARGET_PLATFORM STREQUAL "dos")
   set(DOS ON)
   FetchContent_Declare(SDL2
     # branch: dos-vbe-rebase
-    URL https://github.com/diasurgical/SDL/archive/d9cf9066d9cb796b56d1d70c9c560c055a32149b.tar.gz
-    URL_HASH MD5=9ad9ae69ee0266c895e79cf05a1e0e49
+    URL https://github.com/diasurgical/SDL/archive/b55cac0c06aa191dcc7a3e63ae6fe6656593026e.tar.gz
+    URL_HASH MD5=99eabd2fc675f5539e055b1d8fa519e4
   )
 else()
   FetchContent_Declare(SDL2

CMake/Definitions.cmake

@@ -93,7 +93,8 @@ foreach(
   REMAP_KEYBOARD_KEYS
   DEVILUTIONX_DEFAULT_RESAMPLER
   STREAM_ALL_AUDIO_MIN_FILE_SIZE
-  DEVILUTIONX_DISPLAY_TEXTURE_FORMAT
+  DEVILUTIONX_DISPLAY_PIXELFORMAT # SDL2-only
+  DEVILUTIONX_DISPLAY_TEXTURE_FORMAT # SDL2-only
   DEVILUTIONX_SCREENSHOT_FORMAT
   DARWIN_MAJOR_VERSION
   DARWIN_MINOR_VERSION

CMake/platforms/dos.cmake

@@ -16,6 +16,7 @@ set(DEVILUTIONX_SYSTEM_SDL2 OFF)
 set(DEVILUTIONX_STATIC_SDL2 ON)
 set(DEVILUTIONX_SYSTEM_SDL_IMAGE OFF)
 set(DEVILUTIONX_SYSTEM_LIBPNG OFF)
+set(DEVILUTIONX_DISPLAY_PIXELFORMAT SDL_PIXELFORMAT_INDEX8)
 
 set(DEVILUTIONX_PLATFORM_FILE_UTIL_LINK_LIBRARIES "")
 

Source/engine/dx.cpp

@@ -63,7 +63,12 @@ bool CanRenderDirectlyToOutputSurface()
 	    && outputSurface->format->BitsPerPixel == 8);
 #endif
 #else // !USE_SDL1
-	return false;
+	if (renderer != nullptr) return false;
+	SDL_Surface *outputSurface = GetOutputSurface();
+	// Assumes double-buffering is available.
+	return outputSurface->w == static_cast<int>(gnScreenWidth)
+	    && outputSurface->h == static_cast<int>(gnScreenHeight)
+	    && outputSurface->format->BitsPerPixel == 8;
 #endif
 }
 

Source/storm/storm_svid.cpp

@@ -180,6 +180,11 @@ void UpdatePalette()
 	if (SDL_SetSurfacePalette(SVidSurface.get(), SVidPalette.get()) <= -1) {
 		ErrSdl();
 	}
+	if (GetOutputSurface()->format->BitsPerPixel == 8) {
+		if (SDL_SetSurfacePalette(GetOutputSurface(), SVidPalette.get()) <= -1) {
+			ErrSdl();
+		}
+	}
 #endif
 }
 
@@ -311,6 +316,15 @@ bool SVidPlayBegin(const char *filename, int flags)
 			ErrSdl();
 		}
 	}
+#if defined(DEVILUTIONX_DISPLAY_PIXELFORMAT) && DEVILUTIONX_DISPLAY_PIXELFORMAT == SDL_PIXELFORMAT_INDEX8
+	else {
+		const Size windowSize = { static_cast<int>(SVidWidth), static_cast<int>(SVidHeight) };
+		SDL_DisplayMode nearestDisplayMode = GetNearestDisplayMode(windowSize, DEVILUTIONX_DISPLAY_PIXELFORMAT);
+		if (SDL_SetWindowDisplayMode(ghMainWnd, &nearestDisplayMode) != 0) {
+			ErrSdl();
+		}
+	}
+#endif
 #else
 	TrySetVideoModeToSVidForSDL1();
 #endif
@@ -405,6 +419,15 @@ void SVidPlayEnd()
 			ErrSdl();
 		}
 	}
+#if defined(DEVILUTIONX_DISPLAY_PIXELFORMAT) && DEVILUTIONX_DISPLAY_PIXELFORMAT == SDL_PIXELFORMAT_INDEX8
+	else {
+		const Size windowSize = { static_cast<int>(gnScreenWidth), static_cast<int>(gnScreenHeight) };
+		SDL_DisplayMode nearestDisplayMode = GetNearestDisplayMode(windowSize, DEVILUTIONX_DISPLAY_PIXELFORMAT);
+		if (SDL_SetWindowDisplayMode(ghMainWnd, &nearestDisplayMode) != 0) {
+			ErrSdl();
+		}
+	}
+#endif
 #else
 	if (IsSVidVideoMode) {
 		SetVideoModeToPrimary(IsFullScreen(), gnScreenWidth, gnScreenHeight);

Source/utils/display.cpp

@@ -107,37 +107,6 @@ void CalculatePreferredWindowSize(int &width, int &height)
 		height = mode.h * width / mode.w;
 	}
 }
-
-SDL_DisplayMode GetNearestDisplayMode(Size preferredSize)
-{
-	SDL_DisplayMode nearestDisplayMode;
-	if (SDL_GetWindowDisplayMode(ghMainWnd, &nearestDisplayMode) != 0)
-		ErrSdl();
-
-	const int displayIndex = SDL_GetWindowDisplayIndex(ghMainWnd);
-	const int modeCount = SDL_GetNumDisplayModes(displayIndex);
-	for (int modeIndex = 0; modeIndex < modeCount; modeIndex++) {
-		SDL_DisplayMode displayMode;
-		if (SDL_GetDisplayMode(displayIndex, modeIndex, &displayMode) != 0)
-			continue;
-
-		const int diffHeight = std::abs(nearestDisplayMode.h - preferredSize.height) - std::abs(displayMode.h - preferredSize.height);
-		const int diffWidth = std::abs(nearestDisplayMode.w - preferredSize.width) - std::abs(displayMode.w - preferredSize.width);
-		if (diffHeight < 0)
-			continue;
-		if (diffHeight == 0 && diffWidth < 0)
-			continue;
-		nearestDisplayMode = displayMode;
-	}
-
-	LogVerbose("Nearest display mode to {}x{} is {}x{} {}bpp {}Hz",
-	    preferredSize.width, preferredSize.height,
-	    nearestDisplayMode.w, nearestDisplayMode.h,
-	    SDL_BITSPERPIXEL(nearestDisplayMode.format),
-	    nearestDisplayMode.refresh_rate);
-
-	return nearestDisplayMode;
-}
 #endif
 
 void CalculateUIRectangle()
@@ -299,6 +268,59 @@ const auto OptionChangeHandlerVSync = (GetOptions().Graphics.frameRateControl.Se
 
 } // namespace
 
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+SDL_DisplayMode GetNearestDisplayMode(Size preferredSize, SDL_PixelFormatEnum preferredPixelFormat)
+{
+	SDL_DisplayMode nearestDisplayMode;
+	if (SDL_GetWindowDisplayMode(ghMainWnd, &nearestDisplayMode) != 0)
+		ErrSdl();
+
+	const int displayIndex = SDL_GetWindowDisplayIndex(ghMainWnd);
+	const int modeCount = SDL_GetNumDisplayModes(displayIndex);
+
+	// First, find the best mode among the modes with the requested pixel format.
+	SDL_PixelFormatEnum bestPixelFormat = SDL_PIXELFORMAT_UNKNOWN;
+	for (int modeIndex = 0; modeIndex < modeCount; modeIndex++) {
+		SDL_DisplayMode displayMode;
+		if (SDL_GetDisplayMode(displayIndex, modeIndex, &displayMode) != 0)
+			continue;
+		const int diffHeight = std::abs(nearestDisplayMode.h - preferredSize.height) - std::abs(displayMode.h - preferredSize.height);
+		const int diffWidth = std::abs(nearestDisplayMode.w - preferredSize.width) - std::abs(displayMode.w - preferredSize.width);
+		if (diffHeight < 0)
+			continue;
+		if (diffHeight == 0 && diffWidth < 0)
+			continue;
+		if (preferredPixelFormat == SDL_PIXELFORMAT_UNKNOWN
+		    || displayMode.format == preferredPixelFormat) {
+			nearestDisplayMode = displayMode;
+		}
+	}
+	if (preferredPixelFormat != SDL_PIXELFORMAT_UNKNOWN && bestPixelFormat == SDL_PIXELFORMAT_UNKNOWN) {
+		// If no mode with the preferred pixel format was found, allow any pixel format:
+		for (int modeIndex = 0; modeIndex < modeCount; modeIndex++) {
+			SDL_DisplayMode displayMode;
+			if (SDL_GetDisplayMode(displayIndex, modeIndex, &displayMode) != 0)
+				continue;
+			const int diffHeight = std::abs(nearestDisplayMode.h - preferredSize.height) - std::abs(displayMode.h - preferredSize.height);
+			const int diffWidth = std::abs(nearestDisplayMode.w - preferredSize.width) - std::abs(displayMode.w - preferredSize.width);
+			if (diffHeight < 0)
+				continue;
+			if (diffHeight == 0 && diffWidth < 0)
+				continue;
+			nearestDisplayMode = displayMode;
+		}
+	}
+
+	LogVerbose("Nearest display mode to {}x{} is {}x{} {}bpp {}Hz",
+	    preferredSize.width, preferredSize.height,
+	    nearestDisplayMode.w, nearestDisplayMode.h,
+	    SDL_BITSPERPIXEL(nearestDisplayMode.format),
+	    nearestDisplayMode.refresh_rate);
+
+	return nearestDisplayMode;
+}
+#endif
+
 void AdjustToScreenGeometry(Size windowSize)
 {
 	gnScreenWidth = windowSize.width;
@@ -455,6 +477,13 @@ bool SpawnWindow(const char *lpWindowName)
 
 	ghMainWnd = SDL_CreateWindow(lpWindowName, SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, windowSize.width, windowSize.height, flags);
 
+#if defined(DEVILUTIONX_DISPLAY_PIXELFORMAT)
+	SDL_DisplayMode nearestDisplayMode = GetNearestDisplayMode(windowSize, DEVILUTIONX_DISPLAY_PIXELFORMAT);
+	if (SDL_SetWindowDisplayMode(ghMainWnd, &nearestDisplayMode) != 0) {
+		ErrSdl();
+	}
+#endif
+
 	// Note: https://github.com/libsdl-org/SDL/issues/962
 	// This is a solution to a problem related to SDL mouse grab.
 	// See https://github.com/diasurgical/devilutionX/issues/4251

Source/utils/display.h

@@ -109,4 +109,8 @@ void LogicalToOutput(T *x, T *y)
 #endif
 }
 
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+SDL_DisplayMode GetNearestDisplayMode(Size preferredSize, SDL_PixelFormatEnum preferredPixelFormat = SDL_PIXELFORMAT_UNKNOWN);
+#endif
+
 } // namespace devilution