feat: add sdl2-opengl3 backend impl

src/backend_sdl2_opengl3.zig

@@ -0,0 +1,42 @@
+const zgui = @import("gui.zig");
+
+const SDL_GL_Context = *anyopaque;
+
+pub fn init(window: *anyopaque, context: SDL_GL_Context, glsl_version: []const u8) void {
+    if (!ImGui_ImplSDL2_InitForOpenGL(window, context)) unreachable;
+    if (!ImGui_ImplOpenGL3_Init(glsl_version.ptr)) unreachable;
+}
+
+pub fn deinit() void {
+    ImGui_ImplOpenGL3_Shutdown();
+    ImGui_ImplSDL2_Shutdown();
+}
+
+pub fn newFrame(width: f32, height: f32) void {
+    ImGui_ImplOpenGL3_NewFrame();
+    ImGui_ImplSDL2_NewFrame();
+
+    zgui.io.setDisplaySize(width, height);
+    zgui.io.setDisplayFramebufferScale(1.0, 1.0);
+
+    zgui.newFrame();
+}
+
+pub fn draw() void {
+    zgui.render();
+    ImGui_ImplOpenGL3_RenderDrawData(zgui.getDrawData());
+}
+
+pub fn processEvent(event: *anyopaque) bool {
+    return ImGui_ImplSDL2_ProcessEvent(event);
+}
+
+extern fn ImGui_ImplSDL2_InitForOpenGL(window: *anyopaque, sdl_gl_context: SDL_GL_Context) bool;
+extern fn ImGui_ImplSDL2_Shutdown() void;
+extern fn ImGui_ImplSDL2_NewFrame() void;
+extern fn ImGui_ImplSDL2_ProcessEvent(event: *anyopaque) bool;
+
+extern fn ImGui_ImplOpenGL3_Init(glsl_version: [*]const u8) bool;
+extern fn ImGui_ImplOpenGL3_Shutdown() void;
+extern fn ImGui_ImplOpenGL3_NewFrame() void;
+extern fn ImGui_ImplOpenGL3_RenderDrawData(draw_data: *anyopaque) void;

src/main.zig

@@ -10,6 +10,8 @@ pub usingnamespace @import("gui.zig");
 pub const plot = @import("plot.zig");
 pub const backend = switch (@import("zgui_options").backend) {
     .glfw_wgpu => @import("backend_glfw_wgpu.zig"),
-    .glfw_opengl3 => @import("backend_glfw_opengl3.zig"),
-    .no_backend, .win32_dx12, .sdl2_opengl3 => @panic("unsupported backend"),
+    .glfw_opengl3 => {}, // See glfw-opengl3-backend branch
+    .sdl2_opengl3 => @import("backend_sdl2_opengl3.zig"),
+    .win32_dx12 => .{}, // TODO:
+    .no_backend => .{},
 };