Merge pull request zig-gamedev#20 from vkensou/feature/add_sdl2_backend

add sdl2 backend

Author: hazeycode

libs/imgui/backends/imgui_impl_sdl2.cpp

@@ -138,6 +138,7 @@ static const Uint32 SDL_WINDOW_VULKAN = 0x10000000;
 extern "C" {
 
 bool     ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
+bool     ImGui_ImplSDL2_InitForOther(SDL_Window* window);
 void     ImGui_ImplSDL2_Shutdown();
 void     ImGui_ImplSDL2_NewFrame();
 bool     ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event);

src/backend_sdl2.zig

@@ -1,5 +1,13 @@
 const gui = @import("gui.zig");
 
+pub fn init(
+    window: *const anyopaque, // SDL_Window
+) void {
+    if (!ImGui_ImplSDL2_InitForOther(window)) {
+        unreachable;
+    }
+}
+
 pub fn initOpenGL(
     window: *const anyopaque, // SDL_Window
     context: *const anyopaque, // SDL_GL_Context
@@ -24,6 +32,7 @@ pub fn newFrame() void {
 }
 
 // These functions are defined in `imgui_impl_sdl2.cpp`
+extern fn ImGui_ImplSDL2_InitForOther(window: *const anyopaque) bool;
 extern fn ImGui_ImplSDL2_InitForOpenGL(window: *const anyopaque, sdl_gl_context: *const anyopaque) bool;
 extern fn ImGui_ImplSDL2_ProcessEvent(event: *const anyopaque) bool;
 extern fn ImGui_ImplSDL2_NewFrame() void;