imgui: use freetype for font rendering

src/imgui/CMakeLists.txt

@@ -16,8 +16,16 @@ add_library(imgui STATIC
     imstb_rectpack.h
     imstb_textedit.h
     imstb_truetype.h
+    # imgui Freetype
+    misc/freetype/imgui_freetype.h
+    misc/freetype/imgui_freetype.cpp
 )
 
 if(Boost_FOUND)
     target_link_libraries(imgui PRIVATE boost_headeronly)
 endif()
+
+find_package(Freetype REQUIRED)
+
+target_link_libraries(imgui PRIVATE ${FREETYPE_LIBRARIES})
+target_include_directories(imgui PRIVATE ${FREETYPE_INCLUDE_DIRS})

src/imgui/imconfig.h

@@ -69,7 +69,7 @@
 //---- Use FreeType to build and rasterize the font atlas (instead of stb_truetype which is embedded by default in Dear ImGui)
 // Requires FreeType headers to be available in the include path. Requires program to be compiled with 'misc/freetype/imgui_freetype.cpp' (in this repository) + the FreeType library (not provided).
 // On Windows you may use vcpkg with 'vcpkg install freetype' + 'vcpkg integrate install'.
-//#define IMGUI_ENABLE_FREETYPE
+#define IMGUI_ENABLE_FREETYPE
 
 //---- Use stb_truetype to build and rasterize the font atlas (default)
 // The only purpose of this define is if you want force compilation of the stb_truetype backend ALONG with the FreeType backend.

src/imgui/misc/freetype/README.md

@@ -0,0 +1,37 @@
+# imgui_freetype
+
+Build font atlases using FreeType instead of stb_truetype (which is the default font rasterizer).
+<br>by @vuhdo, @mikesart, @ocornut.
+
+### Usage
+
+1. Get latest FreeType binaries or build yourself (under Windows you may use vcpkg with `vcpkg install freetype`, `vcpkg integrate install`).
+2. Add imgui_freetype.h/cpp alongside your project files.
+3. Add `#define IMGUI_ENABLE_FREETYPE` in your [imconfig.h](https://github.com/ocornut/imgui/blob/master/imconfig.h) file
+
+### About Gamma Correct Blending
+
+FreeType assumes blending in linear space rather than gamma space.
+See FreeType note for [FT_Render_Glyph](https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#FT_Render_Glyph).
+For correct results you need to be using sRGB and convert to linear space in the pixel shader output.
+The default Dear ImGui styles will be impacted by this change (alpha values will need tweaking).
+
+### Testbed for toying with settings (for developers)
+
+See https://gist.github.com/ocornut/b3a9ecf13502fd818799a452969649ad
+
+### Known issues
+
+- Oversampling settins are ignored but also not so much necessary with the higher quality rendering.
+
+### Comparaison
+
+Small, thin anti-aliased fonts are typically benefiting a lots from Freetype's hinting:
+![comparing_font_rasterizers](https://user-images.githubusercontent.com/8225057/107550178-fef87f00-6bd0-11eb-8d09-e2edb2f0ccfc.gif)
+
+### Colorful glyphs/emojis
+
+You can use the `ImGuiFreeTypeBuilderFlags_LoadColor` flag to load certain colorful glyphs. See
+["Using Colorful Glyphs/Emojis"](https://github.com/ocornut/imgui/edit/master/docs/FONTS.md#using-colorful-glyphsemojis) section of FONTS.md.
+
+![colored glyphs](https://user-images.githubusercontent.com/8225057/106171241-9dc4ba80-6191-11eb-8a69-ca1467b206d1.png)