Introduce alternative method for updating window from Lisp bitmap

If the preprocessor symbol SDLRENDERING is defined the code operates as
it previously did.  In the absence of that, we process the Lisp bitmap
into an intermediate form (as before) but then use SDL bitblt to
redraw the intermediate form on the window's surface.

src/sdl.c

@@ -12,8 +12,13 @@
 
 
 static SDL_Window *sdl_window = NULL;
+#if defined(SDLRENDERING)
 static SDL_Renderer *sdl_renderer = NULL;
 static SDL_Texture *sdl_texture = NULL;
+#else
+static SDL_Surface *sdl_windowsurface = NULL;
+static SDL_Surface *sdl_buffersurface = NULL;
+#endif
 static int buffer_size = 0;
 static char *buffer = NULL;
 
@@ -383,6 +388,7 @@ extern MISCSTATS *MiscStats;
 #define MOUSE_RIGHT 14
 #define MOUSE_MIDDLE 15
 static void sdl_update_viewport(int width, int height) {
+  /* XXX: needs work */
   int w = width / 32 * 32;
   if(w > sdl_displaywidth * sdl_pixelscale)
     w = sdl_displaywidth * sdl_pixelscale;
@@ -394,7 +400,9 @@ static void sdl_update_viewport(int width, int height) {
   r.y = 0;
   r.w = w;
   r.h = h;
+#if defined(SDLRENDERING)
   SDL_RenderSetViewport(sdl_renderer, &r);
+#endif
   printf("new viewport: %d / %d\n", w, h);
 }
 static int last_draw = 0;
@@ -425,6 +433,7 @@ void sdl_set_invert(int flag) {
 void sdl_setMousePosition(int x, int y) {
   SDL_WarpMouseInWindow(sdl_window, x, y);
 }
+#if defined(SDLRENDERING)
 void sdl_update_display_rendering() {
   int before = 0;
   int after = 0;
@@ -463,6 +472,45 @@ void sdl_update_display_rendering() {
     //    printf("rendering took %dms\n", after - before);
   }
 }
+#else
+void sdl_update_display_surfaces() {
+  int before = 0;
+  int after = 0;
+  int this_draw = SDL_GetTicks();
+
+  /* check if there's anything to do and sufficient time has elapsed */
+  if (!should_update_texture || this_draw - last_draw <= 16) {
+    return;
+  }
+  before = SDL_GetTicks();
+  sdl_bitblt_to_screen(min_x, min_y, max_x - min_x, max_y - min_y);
+  after = SDL_GetTicks();
+  SDL_Rect r;
+  r.x = min_x;
+  r.y = min_y;
+  r.w = max_x - min_x;
+  r.h = max_y - min_y;
+  if (sdl_pixelscale == 1) {
+    SDL_BlitSurface(sdl_buffersurface, &r, sdl_windowsurface, &r);
+    SDL_UpdateWindowSurfaceRects(sdl_window, &r, 1);
+  } else {
+    SDL_Rect s;
+    s.x = r.x * sdl_pixelscale;
+    s.y = r.y * sdl_pixelscale;
+    s.w = r.w * sdl_pixelscale;
+    s.h = r.h * sdl_pixelscale;
+    SDL_BlitScaled(sdl_buffersurface, &r, sdl_windowsurface, &s);
+    SDL_UpdateWindowSurfaceRects(sdl_window, &s, 1);
+  }
+  min_x = 0;
+  max_x = sdl_displaywidth;
+  min_y = 0;
+  max_y = sdl_displayheight;
+  after = SDL_GetTicks();
+  last_draw = this_draw;
+  //    printf("surface update took %dms\n", after - before);
+}
+#endif
 int process_events_time = 0;
 void process_SDLevents() {
   //  printf("processing events delta %dms\n", SDL_GetTicks() - process_events_time);
@@ -476,6 +524,7 @@ void process_SDLevents() {
     case SDL_WINDOWEVENT:
       switch(event.window.event) {
       case SDL_WINDOWEVENT_RESIZED: {
+        /* XXX: what about integer multiple of 32 requirements here? */
         sdl_windowwidth = event.window.data1;
         sdl_windowheight = event.window.data2;
         sdl_update_viewport(sdl_windowwidth, sdl_windowheight);
@@ -550,8 +599,13 @@ void process_SDLevents() {
       printf("other event type: %d\n", event.type);
     }
   }
+#if defined(SDLRENDERING)
   sdl_update_display_rendering();
+#else
+  sdl_update_display_surfaces();
+#endif
 }
+
 int init_SDL(char *windowtitle, int w, int h, int s) {
   sdl_pixelscale = s;
   // width must be multiple of 32
@@ -578,6 +632,9 @@ int init_SDL(char *windowtitle, int w, int h, int s) {
     printf("Window could not be created. SDL_Error: %s\n", SDL_GetError());
     return 2;
   }
+  buffer_size = width * height * sizeof(char);
+  buffer = malloc(buffer_size);
+#if defined(SDLRENDERING)
   printf("Creating renderer...\n");
   sdl_renderer = SDL_CreateRenderer(sdl_window, -1, SDL_RENDERER_ACCELERATED);
   if(NULL == sdl_renderer) {
@@ -588,8 +645,12 @@ int init_SDL(char *windowtitle, int w, int h, int s) {
   SDL_RenderSetScale(sdl_renderer, 1.0, 1.0);
   printf("Creating texture...\n");
   sdl_texture = SDL_CreateTexture(sdl_renderer, SDL_PIXELFORMAT_RGB332, SDL_TEXTUREACCESS_STREAMING, width, height);
-  buffer_size = width * height * sizeof(char);
-  buffer = malloc(buffer_size);
+#else
+  printf("Creating window surface and buffer surface\n");
+  sdl_windowsurface = SDL_GetWindowSurface(sdl_window);
+  sdl_buffersurface = SDL_CreateRGBSurfaceWithFormatFrom(buffer, sdl_displaywidth, sdl_displayheight, 8,
+                                                         sdl_displaywidth, SDL_PIXELFORMAT_RGB332);
+#endif
   printf("SDL initialised\n");
   return 0;
 }