Add an SDL_Renderer backend to imgui-lwjgl3 and imgui-app

README.md

@@ -49,6 +49,8 @@ cd imgui-java
 ./gradlew :example:run
 # SDL3 + SDL_GPU backend smoke test:
 ./gradlew :example:run -PmainClass=MainSdl
+# SDL3 + SDL_Renderer backend smoke test:
+./gradlew :example:run -PmainClass=MainSdlRenderer
 ```
 
 `example/src/main/java/` contains a runnable showcase for every widget and extension — start with `Main.java`, then
@@ -68,10 +70,11 @@ On Apple Silicon nothing extra is needed: the published macOS native is a univer
 
 ### SDL3 backend (imgui-app)
 
-`imgui-app` now supports two backends via `Configuration#setBackend(...)`:
+`imgui-app` now supports three backends via `Configuration#setBackend(...)`:
 
 - `Backend.GLFW` (default)
 - `Backend.SDL` (SDL3 + SDL_GPU)
+- `Backend.SDL_RENDERER` (SDL3 + `SDL_Renderer`)
 
 Use SDL3 by switching backend in `configure(...)`:
 
@@ -88,7 +91,13 @@ For a ready smoke-test entry point, run `MainSdl`:
 ./gradlew :example:run -PmainClass=MainSdl
 ```
 
-At the moment, SDL backend in `imgui-app` is focused on single-window flow (multi-viewport is not supported).
+The SDL_Renderer variant is available through `Backend.SDL_RENDERER` and the `MainSdlRenderer` smoke test:
+
+```
+./gradlew :example:run -PmainClass=MainSdlRenderer
+```
+
+At the moment, SDL backends in `imgui-app` are focused on single-window flow (multi-viewport is not supported).
 
 ## Application
 

example/src/main/java/MainSdlRenderer.java

@@ -0,0 +1,29 @@
+import imgui.ImGui;
+import imgui.app.Application;
+import imgui.app.Backend;
+import imgui.app.Configuration;
+
+/**
+ * Smoke-test entry point for the SDL3 + SDL_Renderer backend. Run with:
+ * <pre>
+ * ./gradlew :example:run -PmainClass=MainSdlRenderer
+ * </pre>
+ */
+public class MainSdlRenderer extends Application {
+    @Override
+    protected void configure(final Configuration config) {
+        config.setTitle("Example Application — SDL3 + SDL_Renderer");
+        config.setBackend(Backend.SDL_RENDERER);
+    }
+
+    @Override
+    public void process() {
+        ImGui.begin("SDL3 + SDL_Renderer");
+        ImGui.text("Hello from the SDL_Renderer backend!");
+        ImGui.end();
+    }
+
+    public static void main(final String[] args) {
+        launch(new MainSdlRenderer());
+    }
+}

imgui-app/src/main/java/imgui/app/Application.java

@@ -9,7 +9,8 @@
  * <h2>Life-cycle</h2>
  * <p>The entry point for ImGui applications is the Application class and {@link #launch(Application)} method.
  * It builds a {@link Configuration}, lets the user customize it (including selecting a {@link Backend}), then
- * instantiates the matching {@link Window} subclass ({@link WindowGlfw} or {@link WindowSdl}) and drives the
+ * instantiates the matching {@link Window} subclass ({@link WindowGlfw}, {@link WindowSdl} or
+ * {@link WindowSdlRenderer}) and drives the
  * application loop:
  *
  * <ol>
@@ -134,7 +135,18 @@ public final Color getColorBg() {
     public static void launch(final Application app) {
         final Configuration config = new Configuration();
         app.configure(config);
-        app.window = (config.getBackend() == Backend.SDL) ? new WindowSdl() : new WindowGlfw();
+        switch (config.getBackend()) {
+            case SDL:
+                app.window = new WindowSdl();
+                break;
+            case SDL_RENDERER:
+                app.window = new WindowSdlRenderer();
+                break;
+            case GLFW:
+            default:
+                app.window = new WindowGlfw();
+                break;
+        }
         app.window.setOwner(app);
         app.window.init(config);
         app.preRun();

imgui-app/src/main/java/imgui/app/Backend.java

@@ -11,5 +11,9 @@ public enum Backend {
     /**
      * SDL3 platform + SDL_GPU renderer.
      */
-    SDL
+    SDL,
+    /**
+     * SDL3 platform + SDL_Renderer renderer.
+     */
+    SDL_RENDERER
 }

imgui-app/src/main/java/imgui/app/Window.java

@@ -2,7 +2,7 @@
 
 /**
  * Abstract base for an application window. Subclasses bind a specific platform/renderer pair
- * (see {@link WindowGlfw}, {@link WindowSdl}) and forward lifecycle hooks back to the owning
+ * (see {@link WindowGlfw}, {@link WindowSdl}, {@link WindowSdlRenderer}) and forward lifecycle hooks back to the owning
  * {@link Application} via {@link #owner}.
  *
  * <p>Direct subclassing is supported but the supported integration path is to extend

imgui-app/src/main/java/imgui/app/WindowSdlRenderer.java

@@ -0,0 +1,139 @@
+package imgui.app;
+
+import imgui.ImGui;
+import imgui.sdl3.ImGuiImplSdl3;
+import imgui.sdl3.ImGuiImplSdlRenderer3;
+import org.lwjgl.sdl.SDL_Event;
+
+import static org.lwjgl.sdl.SDLError.SDL_GetError;
+import static org.lwjgl.sdl.SDLEvents.SDL_EVENT_QUIT;
+import static org.lwjgl.sdl.SDLEvents.SDL_EVENT_WINDOW_CLOSE_REQUESTED;
+import static org.lwjgl.sdl.SDLEvents.SDL_PollEvent;
+import static org.lwjgl.sdl.SDLInit.SDL_INIT_GAMEPAD;
+import static org.lwjgl.sdl.SDLInit.SDL_INIT_VIDEO;
+import static org.lwjgl.sdl.SDLInit.SDL_Init;
+import static org.lwjgl.sdl.SDLInit.SDL_Quit;
+import static org.lwjgl.sdl.SDLRender.SDL_DestroyRenderer;
+import static org.lwjgl.sdl.SDLRender.SDL_RenderClear;
+import static org.lwjgl.sdl.SDLRender.SDL_RenderPresent;
+import static org.lwjgl.sdl.SDLRender.SDL_SetRenderDrawColorFloat;
+import static org.lwjgl.sdl.SDLRender.SDL_SetRenderScale;
+import static org.lwjgl.sdl.SDLRender.SDL_SetRenderVSync;
+import static org.lwjgl.sdl.SDLRender.nSDL_CreateRenderer;
+import static org.lwjgl.sdl.SDLVideo.SDL_CreateWindow;
+import static org.lwjgl.sdl.SDLVideo.SDL_DestroyWindow;
+import static org.lwjgl.sdl.SDLVideo.SDL_MaximizeWindow;
+import static org.lwjgl.sdl.SDLVideo.SDL_WINDOW_HIGH_PIXEL_DENSITY;
+import static org.lwjgl.sdl.SDLVideo.SDL_WINDOW_RESIZABLE;
+
+/**
+ * SDL3 + {@code SDL_Renderer} implementation of {@link Window}.
+ *
+ * <p>Pumps SDL events through {@link ImGuiImplSdl3#processEvent(long)} each frame and renders through
+ * {@link ImGuiImplSdlRenderer3#renderDrawData(long, long)}. Multi-viewport is not supported.
+ */
+public class WindowSdlRenderer extends Window {
+    private final ImGuiImplSdl3 imGuiSdl3 = new ImGuiImplSdl3();
+    private final ImGuiImplSdlRenderer3 imGuiSdlRenderer3 = new ImGuiImplSdlRenderer3();
+
+    private long handle;
+    private long renderer;
+    private boolean shouldClose;
+
+    @Override
+    protected void init(final Configuration config) {
+        if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMEPAD)) {
+            throw new IllegalStateException("Unable to initialize SDL3: " + SDL_GetError());
+        }
+
+        final long flags = SDL_WINDOW_HIGH_PIXEL_DENSITY | SDL_WINDOW_RESIZABLE;
+        handle = SDL_CreateWindow(config.getTitle(), config.getWidth(), config.getHeight(), flags);
+        if (handle == 0L) {
+            throw new RuntimeException("Failed to create the SDL window: " + SDL_GetError());
+        }
+        if (config.isFullScreen()) {
+            SDL_MaximizeWindow(handle);
+        }
+
+        // Null driver name lets SDL pick the best available renderer.
+        renderer = nSDL_CreateRenderer(handle, 0L);
+        if (renderer == 0L) {
+            throw new RuntimeException("Failed to create the SDL renderer: " + SDL_GetError());
+        }
+        SDL_SetRenderVSync(renderer, 1);
+
+        owner.initImGui(config);
+
+        imGuiSdl3.initForSDLRenderer(handle, renderer);
+        imGuiSdlRenderer3.init(renderer);
+    }
+
+    @Override
+    protected void dispose() {
+        imGuiSdlRenderer3.shutdown();
+        imGuiSdl3.shutdown();
+        owner.disposeImGui();
+
+        if (renderer != 0L) {
+            SDL_DestroyRenderer(renderer);
+            renderer = 0L;
+        }
+        if (handle != 0L) {
+            SDL_DestroyWindow(handle);
+            handle = 0L;
+        }
+        SDL_Quit();
+    }
+
+    @Override
+    protected void run() {
+        while (!shouldClose) {
+            runFrame();
+        }
+    }
+
+    @Override
+    protected void runFrame() {
+        try (SDL_Event event = SDL_Event.calloc()) {
+            while (SDL_PollEvent(event)) {
+                final int type = event.type();
+                imGuiSdl3.processEvent(event.address());
+                if (type == SDL_EVENT_QUIT || type == SDL_EVENT_WINDOW_CLOSE_REQUESTED) {
+                    shouldClose = true;
+                }
+            }
+        }
+
+        imGuiSdlRenderer3.newFrame();
+        imGuiSdl3.newFrame();
+        ImGui.newFrame();
+
+        owner.preProcess();
+        owner.process();
+        owner.postProcess();
+
+        ImGui.render();
+
+        // ImGui works in window coordinates (points) while SDL_Renderer draws in output pixels.
+        // Scale here so the geometry, clip rects and mouse coordinates all share the same space.
+        SDL_SetRenderScale(renderer, ImGui.getIO().getDisplayFramebufferScaleX(), ImGui.getIO().getDisplayFramebufferScaleY());
+        SDL_SetRenderDrawColorFloat(renderer, colorBg.getRed(), colorBg.getGreen(), colorBg.getBlue(), colorBg.getAlpha());
+        SDL_RenderClear(renderer);
+        imGuiSdlRenderer3.renderDrawData(ImGui.getDrawData());
+        SDL_RenderPresent(renderer);
+    }
+
+    /**
+     * @return native {@code SDL_Window*} handle
+     */
+    public final long getHandle() {
+        return handle;
+    }
+
+    /**
+     * @return native {@code SDL_Renderer*} handle
+     */
+    public final long getRenderer() {
+        return renderer;
+    }
+}