backends: add initial GDI backend for windows

Author: mfisher31

.gitignore

@@ -31,4 +31,5 @@ lvtk.includes
 
 doxy.log
 
-.meson-subproject-wrap-hash.txt
+.meson-subproject-wrap-hash.txt.cache/
+.cache/

demo/CMakeLists.txt

@@ -105,4 +105,6 @@ endif()
 if(WIN32)
     lui_add_demo(lui-demo-d2d)
     target_compile_definitions(lui-demo-d2d PRIVATE LUI_DEMO_D2D=1)
+    lui_add_demo(lui-demo-gdi)
+    target_compile_definitions(lui-demo-gdi PRIVATE LUI_DEMO_GDI=1)
 endif()

demo/main.cpp

@@ -18,6 +18,9 @@
 #elif LUI_DEMO_D2D
 #    include <lui/direct2d.hpp>
 #    define LUI_DEMO_TITLE "LUI Direct2D Demo"
+#elif LUI_DEMO_GDI
+#    include <lui/gdi.hpp>
+#    define LUI_DEMO_TITLE "LUI GDI Demo"
 #endif
 
 #include "demo.hpp"
@@ -78,6 +81,8 @@ int WinMain (HINSTANCE hInstance,
     lui::Main context (lui::Mode::PROGRAM, std::make_unique<lui::Vulkan>());
 #    elif LUI_DEMO_D2D
     lui::Main context (lui::Mode::PROGRAM, std::make_unique<lui::Direct2D>());
+#    elif LUI_DEMO_GDI
+    lui::Main context (lui::Mode::PROGRAM, std::make_unique<lui::GDI>());
 #    else
     lui::Main context (lui::Mode::PROGRAM, std::make_unique<lui::OpenGL>());
 #    endif

include/lui/gdi.hpp

@@ -0,0 +1,26 @@
+// Copyright 2026 Kushview, LLC
+// SPDX-License-Identifier: ISC
+
+#pragma once
+
+#include <lui/lui.h>
+#include <lui/main.hpp>
+
+namespace lui {
+
+class Main;
+class Widget;
+
+/** The Windows GDI graphics backend.
+    Using this backend requires Windows and links to GDI.
+
+    @ingroup widgets
+    @ingroup graphics
+    @headerfile lui/gdi.hpp 
+*/
+struct LUI_API GDI : public Backend {
+    GDI() : Backend ("GDI") {}
+    std::unique_ptr<View> create_view (Main& c, Widget& w) override;
+};
+
+} // namespace lui

include/lui/point.hpp

@@ -16,8 +16,8 @@ namespace lui {
 */
 template <typename Val>
 struct Point {
-    static_assert(std::is_integral_v<Val> || std::is_floating_point_v<Val>,
-                  "Point value type must be integral or floating point");
+    static_assert (std::is_integral_v<Val> || std::is_floating_point_v<Val>,
+                   "Point value type must be integral or floating point");
 
     /** X coordinate */
     Val x {};
@@ -26,13 +26,12 @@ struct Point {
 
     Point() = default;
 
-    template<typename TX, typename TY,
-             typename = std::enable_if_t<
-                 (std::is_integral_v<TX> || std::is_floating_point_v<TX>) &&
-                 (std::is_integral_v<TY> || std::is_floating_point_v<TY>)>>
-    Point(TX x_val, TY y_val) noexcept
-        : x(static_cast<Val>(x_val)),
-          y(static_cast<Val>(y_val)) {}
+    template <typename TX, typename TY,
+              typename = std::enable_if_t<
+                  (std::is_integral_v<TX> || std::is_floating_point_v<TX>) && (std::is_integral_v<TY> || std::is_floating_point_v<TY>)>>
+    Point (TX x_val, TY y_val) noexcept
+        : x (static_cast<Val> (x_val)),
+          y (static_cast<Val> (y_val)) {}
 
     /** Convert this point to another value type.
         i.e. int to float

src/CMakeLists.txt

@@ -56,9 +56,11 @@ elseif(UNIX AND NOT APPLE)
         pugl/src/x11.c)
 elseif(WIN32)
     list(APPEND LIBLUI_SOURCES 
-        direct2d.cpp
         embed_win32.cpp
+        direct2d.cpp
         win_direct2d.cpp
+        gdi.cpp
+        win_gdi.c
         pugl/src/win.c)
 endif()