Use render output size to compute content location

The coordinates of the content to render depend on the render output
size, not the window size in pixels. In theory, the two could differ.

app/src/screen.c

@@ -148,34 +148,33 @@ sc_screen_update_content_rect(struct sc_screen *screen) {
     assert(screen->video);
 
     struct sc_size content_size = screen->content_size;
-    // The drawable size is the window size * the HiDPI scale
-    struct sc_size drawable_size =
-        sc_sdl_get_window_size_in_pixels(screen->window);
+    struct sc_size render_size =
+        sc_sdl_get_render_output_size(screen->renderer);
 
     SDL_Rect *rect = &screen->rect;
 
-    if (is_optimal_size(drawable_size, content_size)) {
+    if (is_optimal_size(render_size, content_size)) {
         rect->x = 0;
         rect->y = 0;
-        rect->w = drawable_size.width;
-        rect->h = drawable_size.height;
+        rect->w = render_size.width;
+        rect->h = render_size.height;
         return;
     }
 
-    bool keep_width = content_size.width * drawable_size.height
-                    > content_size.height * drawable_size.width;
+    bool keep_width = content_size.width * render_size.height
+                    > content_size.height * render_size.width;
     if (keep_width) {
         rect->x = 0;
-        rect->w = drawable_size.width;
-        rect->h = drawable_size.width * content_size.height
-                                      / content_size.width;
-        rect->y = (drawable_size.height - rect->h) / 2;
+        rect->w = render_size.width;
+        rect->h = render_size.width * content_size.height
+                                    / content_size.width;
+        rect->y = (render_size.height - rect->h) / 2;
     } else {
         rect->y = 0;
-        rect->h = drawable_size.height;
-        rect->w = drawable_size.height * content_size.width
-                                       / content_size.height;
-        rect->x = (drawable_size.width - rect->w) / 2;
+        rect->h = render_size.height;
+        rect->w = render_size.height * content_size.width
+                                     / content_size.height;
+        rect->x = (render_size.width - rect->w) / 2;
     }
 }
 

app/src/util/sdl.c

@@ -130,6 +130,25 @@ sc_sdl_hide_window(SDL_Window *window) {
     }
 }
 
+struct sc_size
+sc_sdl_get_render_output_size(SDL_Renderer *renderer) {
+    int width;
+    int height;
+    bool ok = SDL_GetRenderOutputSize(renderer, &width, &height);
+    if (!ok) {
+        LOGE("Could not get render output size: %s", SDL_GetError());
+        LOGE("Please report the error");
+        // fatal error
+        abort();
+    }
+
+    struct sc_size size = {
+        .width = width,
+        .height = height,
+    };
+    return size;
+}
+
 bool
 sc_sdl_render_clear(SDL_Renderer *renderer) {
     bool ok = SDL_RenderClear(renderer);

app/src/util/sdl.h

@@ -34,6 +34,9 @@ sc_sdl_show_window(SDL_Window *window);
 void
 sc_sdl_hide_window(SDL_Window *window);
 
+struct sc_size
+sc_sdl_get_render_output_size(SDL_Renderer *renderer);
+
 bool
 sc_sdl_render_clear(SDL_Renderer *renderer);