Added support for scaling the output

* Added "Scale" user option, which can either by "Auto" or an explicit
  scaling factor. Its maximum value depends on the current resolution.

  The "Auto" factor is based on keeping the logical resolution on at
  least 800x600, wheres the maximum scale is based on keeping the
  logical resolution on at least 640x480.

* Enabled support for High DPI. This means the rendering target can now
  have a different resolution than the window size, which can happen on
  macOS, Windows and Wayland. The resulting scale is multiplied by the
  above user-controlled scale.

  Currently, this looks ugly for non-integer scales, which are not used
  on macOS and can only be configured on some Wayland compositors.

  Has not been tested on Windows.

* Simplified OpenGL initialization (moved out of _beginDraw).

* Made sure _beginDraw/_endDraw sets a clip area also for SDLGraphics.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/video.h b/src/video.h
index df9cd518..c98434e6 100644
--- a/src/video.h
+++ b/src/video.h
@@ -49,15 +49,21 @@ struct VideoSettings
     int width = defaultScreenWidth;
     int height = defaultScreenHeight;
     int display = 0;
+    int userScale = 0;
     bool vsync = true;
     bool openGL = false;
 
+    int scale() const;
+    int autoScale() const;
+    int maxScale() const;
+
     bool operator==(const VideoSettings &other) const
     {
         return width == other.width &&
                 height == other.height &&
                 windowMode == other.windowMode &&
                 display == other.display &&
+                userScale == other.userScale &&
                 vsync == other.vsync &&
                 openGL == other.openGL;
     }
@@ -83,6 +89,11 @@ public:
      */
     bool apply(const VideoSettings &settings);
 
+    /**
+     * Handle a change in window size, possibly adjusting the scale.
+     */
+    void windowSizeChanged(int width, int height);
+
     const DisplayMode &desktopDisplayMode() const
     {
         return mDesktopDisplayMode;