adding SDL3_Opengl (zig-gamedev#44)

Author: tonitch

build.zig

@@ -10,7 +10,10 @@ pub const Backend = enum {
     glfw,
     sdl2_opengl3,
     osx_metal,
+    sdl2,
+    sdl3,
     sdl3_gpu,
+    sdl3_opengl3,
 };
 
 pub fn build(b: *std.Build) void {
@@ -338,6 +341,29 @@ pub fn build(b: *std.Build) void {
                 .flags = cflags,
             });
         },
+        .sdl3_opengl3 => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl3/include/SDL3"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl3.cpp",
+                    "libs/imgui/backends/imgui_impl_opengl3.cpp",
+                },
+                .flags = &(cflags.* ++ .{"-DIMGUI_IMPL_OPENGL_LOADER_IMGL3W"}),
+            });
+        },
+        .sdl3 => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl3/include/SDL3"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl3.cpp",
+                },
+                .flags = cflags,
+            });
+        },
         .no_backend => {},
     }
 

src/backend_sdl3.zig

@@ -8,6 +8,15 @@ pub fn initGPU(
     }
 }
 
+pub fn initOpenGL(
+    window: *const anyopaque, // SDL_Window
+    context: *const anyopaque, // SDL_GL_Context
+) void {
+    if (!ImGui_ImplSDL3_InitForOpenGL(window, context)) {
+        unreachable;
+    }
+}
+
 pub fn processEvent(
     event: *const anyopaque, // SDL_Event
 ) bool {
@@ -25,6 +34,13 @@ pub fn newFrame() void {
 // Those functions are defined in `imgui_impl_sdl3.cpp`
 // (they include few custom changes).
 extern fn ImGui_ImplSDL3_InitForSDLGPU(window: *const anyopaque) bool;
+extern fn ImGui_ImplSDL3_InitForOpenGL(window: *const anyopaque, sdl_gl_context: *const anyopaque) bool;
 extern fn ImGui_ImplSDL3_ProcessEvent(event: *const anyopaque) bool;
 extern fn ImGui_ImplSDL3_NewFrame() void;
 extern fn ImGui_ImplSDL3_Shutdown() void;
+
+//TODO: extern fn ImGui_ImplSDL3_InitForVulkan(window: *const anyopaque) bool;
+//TODO: extern fn ImGui_ImplSDL3_InitForD3D(window: *const anyopaque) bool;
+//TODO: extern fn ImGui_ImplSDL3_InitForMetal(window: *const anyopaque) bool;
+//TODO: extern fn ImGui_ImplSDL3_InitForSDLRenderer(window: *const anyopaque, renderer: *const anyopaque) bool;
+//TODO: extern fn ImGui_ImplSDL3_InitForOther(window: *const anyopaque) bool;

src/backend_sdl3_opengl.zig

@@ -0,0 +1,52 @@
+const gui = @import("gui.zig");
+const backend_sdl3 = @import("backend_sdl3.zig");
+
+pub fn initWithGlSlVersion(
+    window: *const anyopaque, // SDL_Window
+    context: *const anyopaque, // SDL_GL_Context
+    glsl_version: ?[:0]const u8, // e.g. "#version 130"
+) void {
+    backend_sdl3.initOpenGL(window, context);
+
+    ImGui_ImplOpenGL3_Init(@ptrCast(glsl_version));
+}
+
+pub fn init(
+    window: *const anyopaque, // SDL_Window
+    context: *const anyopaque, // SDL_GL_Context
+) void {
+    initWithGlSlVersion(window, context, null);
+}
+
+pub fn processEvent(
+    event: *const anyopaque, // SDL_Event
+) bool {
+    return backend_sdl3.processEvent(event);
+}
+
+pub fn deinit() void {
+    ImGui_ImplOpenGL3_Shutdown();
+    backend_sdl3.deinit();
+}
+
+pub fn newFrame(fb_width: u32, fb_height: u32) void {
+    ImGui_ImplOpenGL3_NewFrame();
+    backend_sdl3.newFrame();
+
+    gui.io.setDisplaySize(@as(f32, @floatFromInt(fb_width)), @as(f32, @floatFromInt(fb_height)));
+    gui.io.setDisplayFramebufferScale(1.0, 1.0);
+
+    gui.newFrame();
+}
+
+pub fn draw() void {
+    gui.render();
+    ImGui_ImplOpenGL3_RenderDrawData(gui.getDrawData());
+}
+
+// These functions are defined in 'imgui_impl_opengl3.cpp`
+// (they include few custom changes).
+extern fn ImGui_ImplOpenGL3_Init(glsl_version: [*c]const u8) void;
+extern fn ImGui_ImplOpenGL3_Shutdown() void;
+extern fn ImGui_ImplOpenGL3_NewFrame() void;
+extern fn ImGui_ImplOpenGL3_RenderDrawData(data: *const anyopaque) void;

src/gui.zig

@@ -16,8 +16,11 @@ pub const backend = switch (@import("zgui_options").backend) {
     .glfw_vulkan => @import("backend_glfw_vulkan.zig"),
     .glfw => @import("backend_glfw.zig"),
     .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"),
+    .sdl2_opengl3 => @import("backend_sdl2_opengl.zig"),
+    .sdl3 => @import("backend_sdl3.zig"),
+    .sdl3_opengl3 => @import("backend_sdl3_opengl.zig"),
     .sdl3_gpu => @import("backend_sdl3_gpu.zig"),
     .no_backend => .{},
 };