Detect font scale factor on macOS HiDPI (#246)

Due to Dear ImGui issue ocornut/imgui#5301, the font scaling on HiDPI setup (only on macOS) is not correct and results in blurry text. This PR is a workaround for that.

* simple scale technique worked.
* check DisplayFramebufferScale
* start making a shim
* automatic detection of scale factor on macos
* make nix build succeed.
* remove stale code
* compile shim.mm only on macOS

daemon/app/ghc-specter-daemon/Render.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ForeignFunctionInterface #-}
 {-# LANGUAGE OverloadedRecordDot #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -16,6 +17,7 @@ import Control.Monad.IO.Class (MonadIO (..))
 import Control.Monad.Trans.Reader (ReaderT (runReaderT))
 import Data.Maybe (isNothing)
 import Foreign.C.String (CString, withCString)
+import Foreign.C.Types (CFloat (..))
 import Foreign.Marshal.Alloc (callocBytes, free)
 import Foreign.Marshal.Utils (toBool)
 import Foreign.Ptr (nullPtr)
@@ -45,7 +47,8 @@ import ImGui.Enum
     ImGuiMouseButton_ (..),
   )
 import ImGui.ImGuiIO.Implementation
-  ( imGuiIO_Fonts_get,
+  ( imGuiIO_FontGlobalScale_set,
+    imGuiIO_Fonts_get,
     imGuiIO_MouseWheelH_get,
     imGuiIO_MouseWheel_get,
   )
@@ -71,6 +74,14 @@ import Util.GUI
   )
 import Util.Render (SharedState (..))
 
+#ifdef __MACOS__
+foreign import ccall unsafe "detectScaleFactor"
+  c_detectScaleFactor :: IO CFloat
+#else
+c_detectScaleFactor :: IO CFloat
+c_detectScaleFactor = pure 1.0
+#endif
+
 singleFrame ::
   ImGuiIO ->
   GLFWwindow ->
@@ -183,16 +194,17 @@ prepareAssets io = do
   let free_sans_path = dir </> "assets" </> "FreeSans.ttf"
       free_mono_path = dir </> "assets" </> "FreeMono.ttf"
   fonts <- imGuiIO_Fonts_get io
-  -- _fontDefault <- imFontAtlas_AddFontDefault fonts
+  scale <- c_detectScaleFactor
   _fontDefault <-
     withCString free_sans_path $ \cstr -> do
-      imFontAtlas_AddFontFromFileTTF fonts cstr (8 * 2.0)
+      imFontAtlas_AddFontFromFileTTF fonts cstr (13 * scale)
+  imGuiIO_FontGlobalScale_set io (1.0 / scale)
   fontSans <-
     withCString free_sans_path $ \cstr -> do
-      imFontAtlas_AddFontFromFileTTF fonts cstr 8
+      imFontAtlas_AddFontFromFileTTF fonts cstr (8 * scale)
   fontMono <-
     withCString free_mono_path $ \cstr ->
-      imFontAtlas_AddFontFromFileTTF fonts cstr 8
+      imFontAtlas_AddFontFromFileTTF fonts cstr (8 * scale)
   pure (fontSans, fontMono)
 
 main ::

daemon/app/ghc-specter-daemon/cbits/shim.mm

@@ -0,0 +1,16 @@
+#ifdef __MACOS__
+#include <Cocoa/Cocoa.h>
+#endif
+
+extern "C" {
+
+float detectScaleFactor( void ) {
+#ifdef __MACOS__
+  return NSScreen.mainScreen.backingScaleFactor;
+#else
+  return 1.0;
+#endif
+}
+
+}
+

daemon/ghc-specter-daemon.cabal

@@ -74,6 +74,12 @@ library
       Paths_ghc_specter_daemon
   hs-source-dirs:
       src
+  if os(darwin)
+    cpp-options: -D__MACOS__
+    cxx-options: -D__MACOS__
+    frameworks: Cocoa
+    cxx-sources:
+        app/ghc-specter-daemon/cbits/shim.mm
   ghc-options: -Wall -Wunused-packages -Werror
   build-depends:
       OGDF

flake.nix

@@ -62,7 +62,12 @@
         "ghc-specter-plugin" =
           hself.callCabal2nix "ghc-specter-plugin" ./plugin {};
         "ghc-specter-daemon" =
-          hself.callCabal2nix "ghc-specter-daemon" ./daemon {};
+          final.haskell.lib.overrideCabal
+          (hself.callCabal2nix "ghc-specter-daemon" ./daemon {})
+          (old: {
+            libraryFrameworkDepends =
+              final.lib.optional pkgs.stdenv.isDarwin final.darwin.apple_sdk.frameworks.Cocoa;
+          });
         "ghc-build-analyzer" =
           hself.callCabal2nix "ghc-build-analyzer" ./ghc-build-analyzer {};
       };
@@ -116,7 +121,8 @@
               pkgs.ormolu
               pyenv
             ]
-            ++ (pkgs.lib.optional (pkgs.stdenv.isLinux && !pkgs.lib.inPureEvalMode) nixGL.packages.${system}.default);
+            ++ (pkgs.lib.optional (pkgs.stdenv.isLinux && !pkgs.lib.inPureEvalMode) nixGL.packages.${system}.default)
+            ++ (pkgs.lib.optionals (pkgs.stdenv.isDarwin) [pkgs.darwin.apple_sdk.frameworks.Cocoa]);
           shellHook = ''
             export PS1="\n[${prompt}:\w]$ \0"
           '';