Added handlers for render target loss/window resize

These only really happen when you use exclusive fullscreen and
alt-tab out. Or, at least, it does on Windows with SDL2 in DirectX
mode.

src/Backends/Rendering.h

@@ -21,3 +21,5 @@ void Backend_ColourFillToScreen(const RECT *rect, unsigned char red, unsigned ch
 void Backend_ScreenToSurface(Backend_Surface *surface, const RECT *rect);
 void Backend_DrawText(Backend_Surface *surface, FontObject *font, int x, int y, const char *text, unsigned long colour);
 void Backend_DrawTextToScreen(FontObject *font, int x, int y, const char *text, unsigned long colour);
+void Backend_HandleDeviceLoss(void);
+void Backend_HandleWindowResize(void);

src/Backends/Rendering/SDLTexture.cpp

@@ -14,11 +14,16 @@ struct Backend_Surface
 	BOOL needs_syncing;
 	SDL_Surface *sdl_surface;
 	SDL_Texture *texture;
+
+	struct Backend_Surface *next;
+	struct Backend_Surface *prev;
 };
 
 static SDL_Renderer *renderer;
 static SDL_Texture *screen_texture;
 
+static Backend_Surface *surface_list_head;
+
 static void FlushSurface(Backend_Surface *surface)
 {
 	unsigned char *buffer = (unsigned char*)malloc(surface->sdl_surface->w * surface->sdl_surface->h * 4);
@@ -120,11 +125,21 @@ Backend_Surface* Backend_CreateSurface(unsigned int width, unsigned int height)
 
 	surface->needs_syncing = FALSE;
 
+	surface->next = surface_list_head;
+	if (surface->next)
+		surface->next->prev = surface;
+	surface_list_head = surface;
+
 	return surface;
 }
 
 void Backend_FreeSurface(Backend_Surface *surface)
 {
+	if (surface->next)
+		surface->next->prev = surface->prev;
+	if (surface->prev)
+		surface->prev->next = surface->next;
+
 	SDL_FreeSurface(surface->sdl_surface);
 	free(surface);
 }
@@ -274,3 +289,15 @@ void Backend_DrawTextToScreen(FontObject *font, int x, int y, const char *text,
 	SDL_RenderCopy(renderer, texture, NULL, NULL);
 	SDL_DestroyTexture(texture);
 }
+
+void Backend_HandleDeviceLoss(void)
+{
+	// All of our textures have been lost, so regenerate them
+	for (Backend_Surface *surface = surface_list_head; surface != NULL; surface = surface->next)
+		surface->needs_syncing = TRUE;
+}
+
+void Backend_HandleWindowResize(void)
+{
+	// No problem for us
+}

src/Backends/Rendering/Software.cpp

@@ -83,10 +83,10 @@ void Backend_FreeSurface(Backend_Surface *surface)
 
 void Backend_LoadPixels(Backend_Surface *surface, const unsigned char *pixels, unsigned int width, unsigned int height, unsigned int pitch)
 {
-	for (unsigned int h = 0; h < height; ++h)
+	for (unsigned int i = 0; i < height; ++i)
 	{
-		const unsigned char *src_row = &pixels[h * pitch];
-		unsigned char *dst_row = &surface->pixels[h * surface->pitch];
+		const unsigned char *src_row = &pixels[i * pitch];
+		unsigned char *dst_row = &surface->pixels[i * surface->pitch];
 
 		memcpy(dst_row, src_row, width * 3);
 	}
@@ -231,10 +231,21 @@ void Backend_ScreenToSurface(Backend_Surface *surface, const RECT *rect)
 void Backend_DrawText(Backend_Surface *surface, FontObject *font, int x, int y, const char *text, unsigned long colour)
 {
 	DrawText(font, surface->pixels, surface->pitch, surface->width, surface->height, x, y, colour, text, strlen(text));
-	//surf[surf_no].needs_updating = TRUE;
 }
 
 void Backend_DrawTextToScreen(FontObject *font, int x, int y, const char *text, unsigned long colour)
 {
 	Backend_DrawText(&framebuffer, font, x, y, text, colour);
 }
+
+void Backend_HandleDeviceLoss(void)
+{
+	// No problem for us
+}
+
+void Backend_HandleWindowResize(void)
+{
+	// https://wiki.libsdl.org/SDL_GetWindowSurface
+	// We need to fetch a new surface pointer
+	window_surface = SDL_GetWindowSurface(window);
+}

src/Draw.cpp

@@ -569,3 +569,13 @@ void EndTextObject()
 	UnloadFont(gFont);
 	gFont = NULL;
 }
+
+void HandleDeviceLoss()
+{
+	Backend_HandleDeviceLoss();
+}
+
+void HandleWindowResize()
+{
+	Backend_HandleWindowResize();
+}

src/Draw.h

@@ -72,3 +72,5 @@ void InitTextObject(const char *font_name);
 void PutText(int x, int y, const char *text, unsigned long color);
 void PutText2(int x, int y, const char *text, unsigned long color, Surface_Ids surf_no);
 void EndTextObject();
+void HandleDeviceLoss();
+void HandleWindowResize();

src/Main.cpp

@@ -463,9 +463,19 @@ BOOL SystemTask()
 				return FALSE;
 				break;
 
+			case SDL_RENDER_TARGETS_RESET:
+			case SDL_RENDER_DEVICE_RESET:
+				HandleDeviceLoss();
+				break;
+
 			case SDL_WINDOWEVENT:
 				switch (event.window.event)
 				{
+					case SDL_WINDOWEVENT_RESIZED:
+					case SDL_WINDOWEVENT_SIZE_CHANGED:
+						HandleWindowResize();
+						break;
+
 					case SDL_WINDOWEVENT_FOCUS_GAINED:
 						focusGained = TRUE;
 						ActiveWindow();