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, 5 insertions, 0 deletions

diff --git a/src/gui/setup_video.h b/src/gui/setup_video.h
index d16f6d73..0914f6b1 100644
--- a/src/gui/setup_video.h
+++ b/src/gui/setup_video.h
@@ -31,6 +31,7 @@
 #include <guichan/keylistener.hpp>
 
 class ResolutionListModel;
+class ScaleListModel;
 
 class Setup_Video : public SetupTab, public gcn::ActionListener,
                     public gcn::KeyListener
@@ -45,6 +46,8 @@ class Setup_Video : public SetupTab, public gcn::ActionListener,
         void action(const gcn::ActionEvent &event) override;
 
     private:
+        void refreshScaleList();
+
         VideoSettings mVideoSettings;
         bool mCustomCursorEnabled;
         bool mParticleEffectsEnabled;
@@ -53,6 +56,7 @@ class Setup_Video : public SetupTab, public gcn::ActionListener,
 
         std::unique_ptr<gcn::ListModel> mWindowModeListModel;
         std::unique_ptr<ResolutionListModel> mResolutionListModel;
+        std::unique_ptr<ScaleListModel> mScaleListModel;
 
         //gcn::Label *scrollRadiusLabel;
         //gcn::Label *scrollLazinessLabel;
@@ -61,6 +65,7 @@ class Setup_Video : public SetupTab, public gcn::ActionListener,
 
         gcn::DropDown *mWindowModeDropDown;
         gcn::DropDown *mResolutionDropDown;
+        gcn::DropDown *mScaleDropDown;
         gcn::CheckBox *mVSyncCheckBox;
         gcn::CheckBox *mOpenGLCheckBox;
         gcn::CheckBox *mCustomCursorCheckBox;