id_vl_sdl3: Use SDL3's texture palette support where available

SDL 3.4.0+ is introducing support for palettized textures (at last!):
libsdl-org/SDL@0b4b254
libsdl-org/SDL#6192

This allows us to do the palette resolution on the GPU (or at least, in the
SDL library), instead of manually doing it ourselves, putting the SDL3 render
backend on par with the OpenGL/Vulkan/SDL3_GPU backends.

Further work will explore using the 'pixel art' scaling mode.

Note that building with SDL 3.4.0+ will require SDL 3.4.0+ at runtime.

In the process, fix a few small leaks/errors, too.

Author: sulix

src/id_vl_sdl3.c

@@ -1,8 +1,8 @@
-#include "assert.h"
 #include <SDL3/SDL.h>
 #include <string.h>
 #include "id_vl.h"
 #include "id_vl_private.h"
+#include "id_us.h"
 #include "ck_cross.h"
 
 // We need the window to be exported so we can access it in ID_IN.
@@ -13,6 +13,12 @@ static SDL_Palette *vl_sdl3_palette;
 static SDL_Surface *vl_sdl3_stagingSurface;
 static SDL_Texture *vl_sdl3_scaledTarget;
 static bool vl_sdl3_bilinearSupport = true;
+// Should we resolve the palette on the CPU (as is required pre-SDL-3.4.0)
+#if SDL_VERSION_ATLEAST(3,4,0)
+static bool vl_sdl3_swPalette = false;
+#else
+static bool vl_sdl3_swPalette = true;
+#endif
 
 static void VL_SDL3_ResizeWindow()
 {
@@ -84,14 +90,26 @@ static void VL_SDL3_SetVideoMode(int mode)
 		if (!vl_isIntegerScaled && !vl_sdl3_bilinearSupport)
 			CK_Cross_LogMessage(CK_LOG_MSG_WARNING, "Using SDL3 software renderer without integer scaling. Pixel size may be inconsistent.\n");
 
-		vl_sdl3_texture = SDL_CreateTexture(vl_sdl3_renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_STREAMING, VL_EGAVGA_GFX_WIDTH, VL_EGAVGA_GFX_HEIGHT);
-		SDL_SetTextureScaleMode(vl_sdl3_texture, SDL_SCALEMODE_NEAREST);
+		if (vl_sdl3_swPalette)
+		{
+			vl_sdl3_texture = SDL_CreateTexture(vl_sdl3_renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_STREAMING, VL_EGAVGA_GFX_WIDTH, VL_EGAVGA_GFX_HEIGHT);
+			SDL_SetTextureScaleMode(vl_sdl3_texture, SDL_SCALEMODE_NEAREST);
+			// As we can't do on-GPU palette conversions with SDL3,
+			// we do a PAL8->RGBA conversion of the visible area to this surface each frame.
+			vl_sdl3_stagingSurface = SDL_CreateSurface(VL_EGAVGA_GFX_WIDTH, VL_EGAVGA_GFX_HEIGHT, SDL_PIXELFORMAT_RGBA8888);
+		}
+		else
+		{
+#if SDL_VERSION_ATLEAST(3,4,0)
+			vl_sdl3_texture = SDL_CreateTexture(vl_sdl3_renderer, SDL_PIXELFORMAT_INDEX8, SDL_TEXTUREACCESS_STREAMING, VL_EGAVGA_GFX_WIDTH, VL_EGAVGA_GFX_HEIGHT);
+			SDL_SetTextureScaleMode(vl_sdl3_texture, SDL_SCALEMODE_NEAREST);
+#else
+			Quit("This build requires SDL 3.4.0 or newer!");
+#endif
+		}
 
 		vl_sdl3_palette = SDL_CreatePalette(256);
 
-		// As we can't do on-GPU palette conversions with SDL3,
-		// we do a PAL8->RGBA conversion of the visible area to this surface each frame.
-		vl_sdl3_stagingSurface = SDL_CreateSurface(VL_EGAVGA_GFX_WIDTH, VL_EGAVGA_GFX_HEIGHT, SDL_PIXELFORMAT_RGBA8888);
 
 		VL_SDL3_ResizeWindow();
 		SDL_HideCursor();
@@ -116,7 +134,8 @@ static void *VL_SDL3_CreateSurface(int w, int h, VL_SurfaceUsage usage)
 
 static void VL_SDL3_DestroySurface(void *surface)
 {
-	//TODO: Implement
+	SDL_Surface *surf = (SDL_Surface *)surface;
+	SDL_DestroySurface(surf);
 }
 
 static long VL_SDL3_GetSurfaceMemUse(void *surface)
@@ -189,8 +208,6 @@ static void VL_SDL3_SurfaceRect_PM(void *dst_surface, int x, int y, int w, int h
 
 static void VL_SDL3_SurfaceToSurface(void *src_surface, void *dst_surface, int x, int y, int sx, int sy, int sw, int sh)
 {
-	// Sadly we cannot naively use SDL_BlitSurface, since the surfaces may
-	// both be 8-bit but with different palettes, which we ignore.
 	SDL_Surface *surf = (SDL_Surface *)src_surface;
 	SDL_Surface *dest = (SDL_Surface *)dst_surface;
 
@@ -334,10 +351,22 @@ static void VL_SDL3_Present(void *surface, int scrlX, int scrlY, bool singleBuff
 	SDL_Rect fullRect = {(Sint16)vl_fullRgn_x, (Sint16)vl_fullRgn_y, vl_fullRgn_w, vl_fullRgn_h};
 	SDL_FRect fullRectF = {(float)vl_fullRgn_x, (float)vl_fullRgn_y, (float)vl_fullRgn_w, (float)vl_fullRgn_h};
 
-	SDL_BlitSurface(surf, &srcr, vl_sdl3_stagingSurface, 0);
-	SDL_LockSurface(vl_sdl3_stagingSurface);
-	SDL_UpdateTexture(vl_sdl3_texture, 0, vl_sdl3_stagingSurface->pixels, vl_sdl3_stagingSurface->pitch);
-	SDL_UnlockSurface(vl_sdl3_stagingSurface);
+	if (vl_sdl3_swPalette)
+	{
+		SDL_BlitSurface(surf, &srcr, vl_sdl3_stagingSurface, 0);
+		SDL_LockSurface(vl_sdl3_stagingSurface);
+		SDL_UpdateTexture(vl_sdl3_texture, 0, vl_sdl3_stagingSurface->pixels, vl_sdl3_stagingSurface->pitch);
+		SDL_UnlockSurface(vl_sdl3_stagingSurface);
+	}
+#if SDL_VERSION_ATLEAST(3,4,0)
+	else
+	{
+		SDL_LockSurface(surf);
+		SDL_UpdateTexture(vl_sdl3_texture, 0, (uint8_t *)surf->pixels + (scrlY * surf->pitch) + scrlX, surf->pitch);
+		SDL_UnlockSurface(surf);
+		SDL_SetTexturePalette(vl_sdl3_texture, vl_sdl3_palette);
+	}
+#endif
 	if (vl_sdl3_scaledTarget)
 	{
 		SDL_SetRenderTarget(vl_sdl3_renderer, vl_sdl3_scaledTarget);