backend: Support SDL2

Author: mjakeman

build.zig

@@ -7,6 +7,7 @@ pub const Backend = enum {
     glfw_dx12,
     win32_dx12,
     glfw,
+    sdl2_opengl3,
 };
 
 pub fn build(b: *std.Build) void {
@@ -338,6 +339,18 @@ pub fn build(b: *std.Build) void {
                 .flags = cflags,
             });
         },
+        .sdl2_opengl3 => {
+            if (b.lazyDependency("zsdl", .{})) |zsdl| {
+                imgui.addIncludePath(zsdl.path("libs/sdl2/include"));
+            }
+            imgui.addCSourceFiles(.{
+                .files = &.{
+                    "libs/imgui/backends/imgui_impl_sdl2.cpp",
+                    "libs/imgui/backends/imgui_impl_opengl3.cpp",
+                },
+                .flags = &(cflags.* ++ .{"-DIMGUI_IMPL_OPENGL_LOADER_CUSTOM"}),
+            });
+        },
         .no_backend => {},
     }
 

build.zig.zon

@@ -25,6 +25,10 @@
             .hash = "1220af0752814ec0a3438aa3ca3e33661885ec134c5e7b794247381b0fbe90c21012",
             .lazy = true,
         },
+        .zsdl = .{
+            .path = "../zsdl",
+            .lazy = true,
+        },
         .freetype = .{
             .url = "https://github.com/hexops/freetype/archive/e8c5b37f320db03acba410d993441815bc809606.tar.gz",
             .hash = "1220babb7939707ca390b934657dfd3c8c3a6a78cc9442e4cbd43e3f9ffd49daec9e",

libs/imgui/backends/imgui_impl_sdl2.cpp

@@ -0,0 +1,46 @@
+// dear imgui: Platform Backend for SDL2
+// This needs to be used along with a Renderer (e.g. DirectX11, OpenGL3, Vulkan..)
+// (Info: SDL2 is a cross-platform general purpose library for handling windows, inputs, graphics context creation, etc.)
+
+// Implemented features:
+//  [X] Platform: Clipboard support.
+//  [X] Platform: Mouse support. Can discriminate Mouse/TouchScreen.
+//  [X] Platform: Keyboard support. Since 1.87 we are using the io.AddKeyEvent() function. Pass ImGuiKey values to all key functions e.g. ImGui::IsKeyPressed(ImGuiKey_Space). [Legacy SDL_SCANCODE_* values are obsolete since 1.87 and not supported since 1.91.5]
+//  [X] Platform: Gamepad support. Enabled with 'io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad'.
+//  [X] Platform: Mouse cursor shape and visibility (ImGuiBackendFlags_HasMouseCursors). Disable with 'io.ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange'.
+//  [X] Platform: Basic IME support. App needs to call 'SDL_SetHint(SDL_HINT_IME_SHOW_UI, "1");' before SDL_CreateWindow()!.
+
+// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
+// Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
+// Learn about Dear ImGui:
+// - FAQ                  https://dearimgui.com/faq
+// - Getting Started      https://dearimgui.com/getting-started
+// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
+// - Introduction, links and more at the top of imgui.cpp
+
+#pragma once
+#include "imgui.h"      // IMGUI_IMPL_API
+#ifndef IMGUI_DISABLE
+
+struct SDL_Window;
+struct SDL_Renderer;
+struct _SDL_GameController;
+typedef union SDL_Event SDL_Event;
+
+// Follow "Getting Started" link and check examples/ folder to learn about using backends!
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForVulkan(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForD3D(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForMetal(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForSDLRenderer(SDL_Window* window, SDL_Renderer* renderer);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForOther(SDL_Window* window);
+IMGUI_IMPL_API void     ImGui_ImplSDL2_Shutdown();
+IMGUI_IMPL_API void     ImGui_ImplSDL2_NewFrame();
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event);
+
+// Gamepad selection automatically starts in AutoFirst mode, picking first available SDL_Gamepad. You may override this.
+// When using manual mode, caller is responsible for opening/closing gamepad.
+enum ImGui_ImplSDL2_GamepadMode { ImGui_ImplSDL2_GamepadMode_AutoFirst, ImGui_ImplSDL2_GamepadMode_AutoAll, ImGui_ImplSDL2_GamepadMode_Manual };
+IMGUI_IMPL_API void     ImGui_ImplSDL2_SetGamepadMode(ImGui_ImplSDL2_GamepadMode mode, struct _SDL_GameController** manual_gamepads_array = nullptr, int manual_gamepads_count = -1);
+
+#endif // #ifndef IMGUI_DISABLE

libs/imgui/backends/imgui_impl_sdl2.h

@@ -0,0 +1,30 @@
+const gui = @import("gui.zig");
+
+pub fn initOpenGL(
+    window: *const anyopaque, // SDL_Window
+    context: *const anyopaque, // SDL_GL_Context
+) void {
+    if (!ImGui_ImplSDL2_InitForOpenGL(window, context)) {
+        unreachable;
+    }
+}
+
+pub fn processEvent(
+    event: *const anyopaque, // SDL_Event
+) bool {
+    return ImGui_ImplSDL2_ProcessEvent(event);
+}
+
+pub fn deinit() void {
+    ImGui_ImplSDL2_Shutdown();
+}
+
+pub fn newFrame() void {
+    ImGui_ImplSDL2_NewFrame();
+}
+
+// These functions are defined in `imgui_impl_sdl2.cpp`
+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;
+extern fn ImGui_ImplSDL2_Shutdown() void;

src/backend_sdl2.zig

@@ -0,0 +1,52 @@
+const gui = @import("gui.zig");
+const backend_sdl2 = @import("backend_sdl2.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_sdl2.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_sdl2.processEvent(event);
+}
+
+pub fn deinit() void {
+    ImGui_ImplOpenGL3_Shutdown();
+    backend_sdl2.deinit();
+}
+
+pub fn newFrame(fb_width: u32, fb_height: u32) void {
+    backend_sdl2.newFrame();
+    ImGui_ImplOpenGL3_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/backend_sdl2_opengl.zig

@@ -15,6 +15,7 @@ pub const backend = switch (@import("zgui_options").backend) {
     .glfw_dx12 => @import("backend_glfw_dx12.zig"),
     .glfw => @import("backend_glfw.zig"),
     .win32_dx12 => @import("backend_win32_dx12.zig"),
+    .sdl2_opengl3 => @import("backend_sdl2_opengl.zig"),
     .no_backend => .{},
 };
 const te_enabled = @import("zgui_options").with_te;