add sdl2 backend

Author: vkensou

build.zig

@@ -10,6 +10,7 @@ pub const Backend = enum {
     glfw,
     sdl2_opengl3,
     osx_metal,
+    sdl2,
 };
 
 pub fn build(b: *std.Build) void {
@@ -385,6 +386,17 @@ pub fn build(b: *std.Build) void {
                 .flags = objcflags,
             });
         },
+        .sdl2 => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl2/include"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl2.cpp",
+                },
+                .flags = cflags,
+            });
+        },
         .no_backend => {},
     }
 

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;

src/gui.zig

@@ -18,6 +18,7 @@ pub const backend = switch (@import("zgui_options").backend) {
     .win32_dx12 => @import("backend_win32_dx12.zig"),
     .sdl2_opengl3 => @import("backend_sdl2_opengl.zig"),
     .osx_metal => @import("backend_osx_metal.zig"),
+    .sdl2 => @import("backend_sdl2.zig"),
     .no_backend => .{},
 };
 const te_enabled = @import("zgui_options").with_te;