imgui/examples/example_sdl3_metal/main.mm

// Dear ImGui: standalone example application for SDL3 + Metal
// (SDL is a cross-platform general purpose library for handling windows, inputs, OpenGL/Vulkan/Metal graphics context creation, etc.)

// 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

#include "imgui.h"
#include "imgui_impl_sdl3.h"
#include "imgui_impl_metal.h"
#include <stdio.h>          // printf, fprintf
#include <SDL3/SDL.h>

#import <Metal/Metal.h>
#import <QuartzCore/QuartzCore.h>

// Main code
int main(int, char**)
{
    // Setup SDL
    // [If using SDL_MAIN_USE_CALLBACKS: all code below until the main loop starts would likely be your SDL_AppInit() function]
    if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMEPAD))
    {
        printf("Error: SDL_Init(): %s\n", SDL_GetError());
        return -1;
    }

    // Create SDL window graphics context
    float main_scale = SDL_GetDisplayContentScale(SDL_GetPrimaryDisplay());
    SDL_WindowFlags window_flags = SDL_WINDOW_METAL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIDDEN | SDL_WINDOW_HIGH_PIXEL_DENSITY;
    SDL_Window* window = SDL_CreateWindow("Dear ImGui SDL3+Metal example", (int)(1280 * main_scale), (int)(720 * main_scale), window_flags);
    if (window == nullptr)
    {
        printf("Error: SDL_CreateWindow(): %s\n", SDL_GetError());
        return -1;
    }
    SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
    SDL_ShowWindow(window);

    // Create Metal device _before_ creating the view/layer
    id<MTLDevice> metalDevice = MTLCreateSystemDefaultDevice(); 
    if (!metalDevice)
    {
        printf("Error: failed to create Metal device.\n");
        SDL_DestroyWindow(window);
        SDL_Quit();
        return -1;
    }
    SDL_MetalView view = SDL_Metal_CreateView(window);
    CAMetalLayer* layer = (__bridge CAMetalLayer*)SDL_Metal_GetLayer(view);
    layer.device = metalDevice;
    layer.pixelFormat = MTLPixelFormatBGRA8Unorm;

    id<MTLCommandQueue> commandQueue = [layer.device newCommandQueue];
    MTLRenderPassDescriptor* renderPassDescriptor = [MTLRenderPassDescriptor new];

    // Setup Dear ImGui context
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO(); (void)io;
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;      // Enable Gamepad Controls

    // Setup Dear ImGui style
    ImGui::StyleColorsDark();
    //ImGui::StyleColorsLight();

    // Setup scaling
    ImGuiStyle& style = ImGui::GetStyle();
    style.ScaleAllSizes(main_scale);        // Bake a fixed style scale. (until we have a solution for dynamic style scaling, changing this requires resetting Style + calling this again)
    style.FontScaleDpi = main_scale;        // Set initial font scale. (using io.ConfigDpiScaleFonts=true makes this unnecessary. We leave both here for documentation purpose)

    // Setup Platform/Renderer backends
    ImGui_ImplMetal_Init(layer.device);
    ImGui_ImplSDL3_InitForMetal(window);

    // Load Fonts
    // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
    // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.
    // - If the file cannot be loaded, the function will return a nullptr. Please handle those errors in your application (e.g. use an assertion, or display an error and quit).
    // - Use '#define IMGUI_ENABLE_FREETYPE' in your imconfig file to use Freetype for higher quality font rendering.
    // - Read 'docs/FONTS.md' for more instructions and details.
    // - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
    //style.FontSizeBase = 20.0f;
    //io.Fonts->AddFontDefault();
    //io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\segoeui.ttf");
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf");
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf");
    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf");
    //ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf");
    //IM_ASSERT(font != nullptr);

    // Our state
    bool show_demo_window = true;
    bool show_another_window = false;
    float clear_color[4] = { 0.45f, 0.55f, 0.60f, 1.00f };

    // Main loop
    bool done = false;
    while (!done)
    {
        @autoreleasepool
        {
            // Poll and handle events (inputs, window resize, etc.)
            // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
            // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
            // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
            // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
            // [If using SDL_MAIN_USE_CALLBACKS: call ImGui_ImplSDL3_ProcessEvent() from your SDL_AppEvent() function]
            SDL_Event event;
            while (SDL_PollEvent(&event))
            {
                ImGui_ImplSDL3_ProcessEvent(&event);
                if (event.type == SDL_EVENT_QUIT)
                    done = true;
                if (event.type == SDL_EVENT_WINDOW_CLOSE_REQUESTED && event.window.windowID == SDL_GetWindowID(window))
                    done = true;
            }

            // [If using SDL_MAIN_USE_CALLBACKS: all code below would likely be your SDL_AppIterate() function]
            if (SDL_GetWindowFlags(window) & SDL_WINDOW_MINIMIZED)
            {
                SDL_Delay(10);
                continue;
            }

            int width, height;
            SDL_GetWindowSizeInPixels(window, &width, &height);
        
            layer.drawableSize = CGSizeMake(width, height);
            id<CAMetalDrawable> drawable = [layer nextDrawable];

            id<MTLCommandBuffer> commandBuffer = [commandQueue commandBuffer];
            renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(clear_color[0] * clear_color[3], clear_color[1] * clear_color[3], clear_color[2] * clear_color[3], clear_color[3]);
            renderPassDescriptor.colorAttachments[0].texture = drawable.texture;
            renderPassDescriptor.colorAttachments[0].loadAction = MTLLoadActionClear;
            renderPassDescriptor.colorAttachments[0].storeAction = MTLStoreActionStore;
            id <MTLRenderCommandEncoder> renderEncoder = [commandBuffer renderCommandEncoderWithDescriptor:renderPassDescriptor];
            [renderEncoder pushDebugGroup:@"ImGui demo"];

            // Start the Dear ImGui frame
            ImGui_ImplMetal_NewFrame(renderPassDescriptor);
            ImGui_ImplSDL3_NewFrame();
            ImGui::NewFrame();

            // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
            if (show_demo_window)
                ImGui::ShowDemoWindow(&show_demo_window);

            // 2. Show a simple window that we create ourselves. We use a Begin/End pair to create a named window.
            {
                static float f = 0.0f;
                static int counter = 0;

                ImGui::Begin("Hello, world!");                          // Create a window called "Hello, world!" and append into it.

                ImGui::Text("This is some useful text.");               // Display some text (you can use a format strings too)
                ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our window open/close state
                ImGui::Checkbox("Another Window", &show_another_window);

                ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f
                ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color

                if (ImGui::Button("Button"))                            // Buttons return true when clicked (most widgets return true when edited/activated)
                    counter++;
                ImGui::SameLine();
                ImGui::Text("counter = %d", counter);

                ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / io.Framerate, io.Framerate);
                ImGui::End();
            }

            // 3. Show another simple window.
            if (show_another_window)
            {
                ImGui::Begin("Another Window", &show_another_window);   // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
                ImGui::Text("Hello from another window!");
                if (ImGui::Button("Close Me"))
                    show_another_window = false;
                ImGui::End();
            }

            // Rendering
            ImGui::Render();
            ImDrawData* draw_data = ImGui::GetDrawData();
            ImGui_ImplMetal_RenderDrawData(draw_data, commandBuffer, renderEncoder);

            [renderEncoder popDebugGroup];
            [renderEncoder endEncoding];

            [commandBuffer presentDrawable:drawable];
            [commandBuffer commit];
        }
    }

    // Cleanup
    // [If using SDL_MAIN_USE_CALLBACKS: all code below would likely be your SDL_AppQuit() function]
    ImGui_ImplMetal_Shutdown();
    ImGui_ImplSDL3_Shutdown();
    ImGui::DestroyContext();

    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}