Render to a small texture, then scale up to the screen size

To be honest, I thought this is what SDL_RenderSetLogicalSize() did, but
actually it scales up each object that you draw with SDL_RenderCopy().
This is necessary because on some GPUs, scaling up can cause a sprite to
bleed into an adjacent frame in the spritesheet texture.

This shouldn't happen with nearest neighbor scaling, but it nevertheless
does happen on some GPUs such as my laptop's embedded Intel GPU. On this
GPU I saw a one pixel wide strip on the top and left of every sprite
that showed the neighboring sprite frame. The strip was one pixel wide
in my screen's pixels, not the logical resolution's pixels. Rendering
everything to a 320x240 texture and then scaling up the whole texture at
once makes strange bugs like this impossible.

src/endgame/island.cpp

@@ -80,7 +80,7 @@ void island_draw()
 {
 
   // draw the scene
-  Renderer::getInstance()->fillScreen(BLACK);
+  Renderer::getInstance()->clearScreen(BLACK);
 
   Renderer::getInstance()->setClip(island.scene_x, island.scene_y, Renderer::getInstance()->sprites.sprites[SPR_ISLAND_SCENE].w, Renderer::getInstance()->sprites.sprites[SPR_ISLAND_SCENE].h);
 

src/game.cpp

@@ -220,7 +220,7 @@ bool Game::pause(int pausemode, int param)
 
 void Game::tick(void)
 {
-  Renderer::getInstance()->clearScreen();
+  Renderer::getInstance()->clearScreen(BLACK);
   debug_clear();
 
   if (game.paused)
@@ -353,7 +353,7 @@ void DrawScene(void)
 {
   int scr_x, scr_y;
   extern int flipacceltime;
-  Renderer::getInstance()->fillScreen(BLACK);
+  Renderer::getInstance()->clearScreen(BLACK);
 
   // draw background map tiles
   if (!flipacceltime)

src/graphics/Renderer.cpp

@@ -69,6 +69,7 @@ bool Renderer::initVideo(int scale)
 {
   uint32_t window_flags = SDL_WINDOW_SHOWN | SDL_WINDOW_ALLOW_HIGHDPI;
 
+  //TODO: sync this with setResolution
   if (widescreen) {
     screenWidth  = 432;
     screenHeight = 243;
@@ -138,6 +139,9 @@ bool Renderer::initVideo(int scale)
     return false;
   }
 
+  if (!createRenderTarget(screenWidth, screenHeight))
+    return false;
+
   std::string spotpath = ResourceManager::getInstance()->getPath("spot.png");
 
   SDL_Surface *image;
@@ -148,6 +152,24 @@ bool Renderer::initVideo(int scale)
   return true;
 }
 
+bool Renderer::createRenderTarget(int width, int height)
+{
+  SDL_RendererInfo info;
+  SDL_GetRendererInfo(_renderer, &info);
+
+  _texture = SDL_CreateTexture(_renderer,
+      info.texture_formats[0],
+      SDL_TEXTUREACCESS_TARGET,
+      width, height);
+  if (SDL_SetRenderTarget(_renderer, _texture)) {
+    LOG_ERROR("Renderer::createRenderTarget: SDL_SetRenderTarget failed: {}", SDL_GetError());
+    return false;
+  }
+  SDL_RenderClear(_renderer);
+
+  return true;
+}
+
 bool Renderer::flushAll()
 {
   LOG_DEBUG("Renderer::flushAll()");
@@ -200,18 +222,24 @@ bool Renderer::setResolution(int scale, bool newWidescreen)
   LOG_INFO("Renderer logical resolution: {}x{}", newWidth, newHeight);
 
   SDL_SetWindowSize(_window, newWidth * scale, newHeight * scale);
+
+  SDL_SetRenderTarget(_renderer, NULL);
+  SDL_DestroyTexture(_texture);
   if (SDL_RenderSetLogicalSize(_renderer, newWidth, newHeight)) {
     LOG_ERROR("Renderer::setResolution: SDL_RenderSetLogicalSize failed: {}", SDL_GetError());
     return false;
   }
 
+  if (!flushAll())
+    return false;
+
+  if (!createRenderTarget(newWidth, newHeight))
+    return false;
+
   screenWidth = newWidth;
   screenHeight = newHeight;
   widescreen = newWidescreen;
 
-  if (!flushAll())
-    return false;
-
   recalc_map_offsets();
   textbox.RecalculateOffsets();
 
@@ -237,7 +265,7 @@ void Renderer::showLoadingScreen()
   int x = (screenWidth / 2) - (loading.width() / 2);
   int y = (screenHeight / 2) - loading.height();
 
-  fillScreen(BLACK);
+  clearScreen(BLACK);
   drawSurface(&loading, x, y);
   flip();
 }
@@ -252,16 +280,15 @@ SDL_Window* Renderer::window()
   return _window;
 }
 
-void Renderer::clearScreen()
-{
-  SDL_SetRenderDrawColor(_renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
-  SDL_RenderClear(_renderer);
-}
-
 void Renderer::flip()
 {
 //  LOG_INFO("===FLIPPING===\n");
+  SDL_SetRenderTarget(_renderer, NULL);
+  SDL_SetRenderDrawColor(_renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
+  SDL_RenderClear(_renderer);
+  SDL_RenderCopy(_renderer, _texture, NULL, NULL);
   SDL_RenderPresent(_renderer);
+  SDL_SetRenderTarget(_renderer, _texture);
 //  LOG_INFO("===FLIPPED===\n");
 }
 
@@ -390,7 +417,7 @@ void Renderer::drawPixel(int x, int y, uint8_t r, uint8_t g, uint8_t b)
   fillRect(x, y, x, y, r, g, b);
 }
 
-void Renderer::fillScreen(uint8_t r, uint8_t g, uint8_t b)
+void Renderer::clearScreen(uint8_t r, uint8_t g, uint8_t b)
 {
   SDL_SetRenderDrawColor(_renderer, r, g, b, SDL_ALPHA_OPAQUE);
   SDL_RenderFillRect(_renderer, NULL);

src/graphics/Renderer.h

@@ -48,16 +48,14 @@ class Renderer
 
     void showLoadingScreen();
 
-    void clearScreen();
-
     void drawSurface(Surface *src, int x, int y);
     void drawSurface(Surface *src, int dstx, int dsty, int srcx, int srcy, int wd, int ht);
     void drawSurfaceMirrored(Surface *src, int dstx, int dsty, int srcx, int srcy, int wd, int ht);
 
     void blitPatternAcross(Surface *sfc, int x_dst, int y_dst, int y_src, int height);
 
-    void fillScreen(NXColor color);
-    void fillScreen(uint8_t r, uint8_t g, uint8_t b);
+    void clearScreen(NXColor color);
+    void clearScreen(uint8_t r, uint8_t g, uint8_t b);
 
     void drawLine(int x1, int y1, int x2, int y2, NXColor color);
 
@@ -96,12 +94,15 @@ class Renderer
   private:
     SDL_Window *_window = nullptr;
     SDL_Renderer *_renderer = nullptr;
+    SDL_Texture *_texture = nullptr;
     int _current_res = -1;
     bool _need_clip = false;
     SDL_Rect _clip_rect;
     SDL_Texture* _spot_light;
     bool _fullscreen = false;
 
+    bool createRenderTarget(int width, int height);
+
   protected:
     friend class Singleton<Renderer>;
 
@@ -151,9 +152,9 @@ void inline Renderer::drawPixel(int x, int y, NXColor color)
   drawPixel(x, y, color.r, color.g, color.b);
 }
 
-void inline Renderer::fillScreen(NXColor color)
+void inline Renderer::clearScreen(NXColor color)
 {
-  fillScreen(color.r, color.g, color.b);
+  clearScreen(color.r, color.g, color.b);
 }
 
 void inline Renderer::setClip(NXRect *rect)

src/intro/intro.cpp

@@ -43,7 +43,7 @@ void intro_tick()
   }
   if (blanktimer > 0)
   {
-    Renderer::getInstance()->fillScreen(BLACK);
+    Renderer::getInstance()->clearScreen(BLACK);
 
     if (--blanktimer == 0)
       game.setmode(GM_TITLE);

src/intro/title.cpp

@@ -62,7 +62,7 @@ std::vector<menuitem> _menuitems;
 static void draw_title()
 {
   // background is dk grey, not pure black
-  Renderer::getInstance()->fillScreen(0x20, 0x20, 0x20);
+  Renderer::getInstance()->clearScreen(0x20, 0x20, 0x20);
   map_draw_backdrop();
   //	DrawFastLeftLayered();
 
@@ -343,7 +343,7 @@ void title_tick()
   {
     if (title.seldelay > 0)
     {
-      Renderer::getInstance()->fillScreen(BLACK);
+      Renderer::getInstance()->clearScreen(BLACK);
 
       title.seldelay--;
       if (!title.seldelay)
@@ -357,7 +357,7 @@ void title_tick()
   }
   else
   {
-    Renderer::getInstance()->fillScreen(BLACK);
+    Renderer::getInstance()->clearScreen(BLACK);
 
     if (!textbox.SaveSelect.IsVisible())
     { // selection was made, and settings.last_save_slot is now set appropriately

src/map.cpp

@@ -588,9 +588,9 @@ void map_draw_backdrop(void)
     case BK_HIDE3:
     {
       if (game.curmap == STAGE_KINGS) // intro cutscene
-        Renderer::getInstance()->fillScreen(BLACK);
+        Renderer::getInstance()->clearScreen(BLACK);
       else
-        Renderer::getInstance()->fillScreen(DK_BLUE);
+        Renderer::getInstance()->clearScreen(DK_BLUE);
     }
       return;
 
@@ -644,15 +644,15 @@ void DrawFastLeftLayered(void)
   y1 = x = 0;
   // fix for extra height
   if (map.backdrop == 9)
-    Renderer::getInstance()->fillScreen(111, 156, 214);
+    Renderer::getInstance()->clearScreen(111, 156, 214);
   else if (map.backdrop == 10 && game.curmap != 64)
-    Renderer::getInstance()->fillScreen(107, 105, 82);
+    Renderer::getInstance()->clearScreen(107, 105, 82);
   else if (map.backdrop == 12)
-    Renderer::getInstance()->fillScreen(179, 190, 210);
+    Renderer::getInstance()->clearScreen(179, 190, 210);
   else if (map.backdrop == 13)
-    Renderer::getInstance()->fillScreen(170, 101, 0);
+    Renderer::getInstance()->clearScreen(170, 101, 0);
   else if (map.backdrop == 14)
-    Renderer::getInstance()->fillScreen(202, 97, 97);
+    Renderer::getInstance()->clearScreen(202, 97, 97);
 
   for (i = 0; i < nlayers; i++)
   {

src/pause/mods.cpp

@@ -72,7 +72,7 @@ bool mods_init(int param)
 void mods_tick()
 {
    if (moddlg != NULL) {
-       Renderer::getInstance()->fillScreen(BLACK);
+       Renderer::getInstance()->clearScreen(BLACK);
        moddlg->Draw();
        moddlg->RunInput();
    }

src/pause/options.cpp

@@ -113,7 +113,7 @@ void options_tick()
   unsigned int i;
   FocusHolder *fh;
 
-  Renderer::getInstance()->fillScreen(BLACK);
+  Renderer::getInstance()->clearScreen(BLACK);
   Options::run_and_draw_objects();
 
   fh = (FocusHolder *)optionstack.at(optionstack.size() - 1);

src/screeneffect.cpp

@@ -41,7 +41,7 @@ void SE_FlashScreen::Draw(void)
   }
 
   if (flashstate)
-    Renderer::getInstance()->fillScreen(0xff, 0xff, 0xff);
+    Renderer::getInstance()->clearScreen(0xff, 0xff, 0xff);
 }
 
 /*
@@ -170,7 +170,7 @@ void SE_Fade::Draw(void)
   }
   else if (state == FS_FADED_OUT)
   {
-    Renderer::getInstance()->fillScreen(DK_BLUE);
+    Renderer::getInstance()->clearScreen(DK_BLUE);
     return;
   }