Fix ImGui window framebuffer clearing

Author: Sunrisepeak

examples/glfw_opengl3/src/main.cpp

@@ -50,6 +50,12 @@ int main() {
         ImGui::End();
         ImGui::Render();
 
+        int framebufferWidth = 0;
+        int framebufferHeight = 0;
+        ImGui::Backend::GlfwOpenGL3::GetFramebufferSize(window, &framebufferWidth, &framebufferHeight);
+        ImGui::Backend::GlfwOpenGL3::Viewport(0, 0, framebufferWidth, framebufferHeight);
+        ImGui::Backend::GlfwOpenGL3::ClearColor(0.08f, 0.09f, 0.10f, 1.0f);
+        ImGui::Backend::GlfwOpenGL3::ClearColorBuffer();
         ImGui::Backend::GlfwOpenGL3::RenderDrawData(ImGui::GetDrawData());
         ImGui::Backend::GlfwOpenGL3::SwapBuffers(window);
 

examples/minimal_window/src/main.cpp

@@ -65,6 +65,12 @@ int main() {
         ImGui::End();
         ImGui::Render();
 
+        int framebufferWidth = 0;
+        int framebufferHeight = 0;
+        Backend::GetFramebufferSize(window, &framebufferWidth, &framebufferHeight);
+        Backend::Viewport(0, 0, framebufferWidth, framebufferHeight);
+        Backend::ClearColor(0.08f, 0.09f, 0.10f, 1.0f);
+        Backend::ClearColorBuffer();
         Backend::RenderDrawData(ImGui::GetDrawData());
         Backend::SwapBuffers(window);
     }

src/backends/glfw.cppm

@@ -63,6 +63,10 @@ export namespace ImGui::Backend::Glfw {
         glfwMakeContextCurrent(window);
     }
 
+    void GetFramebufferSize(Window* window, int* width, int* height) {
+        glfwGetFramebufferSize(window, width, height);
+    }
+
     void SwapInterval(int interval) {
         glfwSwapInterval(interval);
     }

src/backends/glfw_opengl3.cppm

@@ -54,6 +54,10 @@ export namespace ImGui::Backend::GlfwOpenGL3 {
         Glfw::MakeContextCurrent(window);
     }
 
+    void GetFramebufferSize(Window* window, int* width, int* height) {
+        Glfw::GetFramebufferSize(window, width, height);
+    }
+
     void SwapInterval(int interval) {
         Glfw::SwapInterval(interval);
     }
@@ -111,6 +115,18 @@ export namespace ImGui::Backend::GlfwOpenGL3 {
         Glfw::NewFrame();
     }
 
+    void Viewport(int x, int y, int width, int height) {
+        OpenGL3::Viewport(x, y, width, height);
+    }
+
+    void ClearColor(float red, float green, float blue, float alpha) {
+        OpenGL3::ClearColor(red, green, blue, alpha);
+    }
+
+    void ClearColorBuffer() {
+        OpenGL3::ClearColorBuffer();
+    }
+
     void RenderDrawData(ImDrawData* drawData) {
         OpenGL3::RenderDrawData(drawData);
     }

src/backends/opengl3.cppm

@@ -1,6 +1,7 @@
 module;
 
 #include <imgui_impl_opengl3.h>
+#include <imgui_impl_opengl3_loader.h>
 
 export module imgui.backend.opengl3;
 
@@ -19,6 +20,18 @@ export namespace ImGui::Backend::OpenGL3 {
         ImGui_ImplOpenGL3_NewFrame();
     }
 
+    void Viewport(int x, int y, int width, int height) {
+        glViewport(x, y, width, height);
+    }
+
+    void ClearColor(float red, float green, float blue, float alpha) {
+        glClearColor(red, green, blue, alpha);
+    }
+
+    void ClearColorBuffer() {
+        glClear(GL_COLOR_BUFFER_BIT);
+    }
+
     void RenderDrawData(ImDrawData* drawData) {
         ImGui_ImplOpenGL3_RenderDrawData(drawData);
     }

tests/backend_test.cpp

@@ -16,6 +16,7 @@ TEST(ImGuiGlfwBackendModuleTest, ExposesPlatformApi) {
     auto restoreCallbacks = &ImGui::Backend::Glfw::RestoreCallbacks;
     auto getContentScaleForWindow = &ImGui::Backend::Glfw::GetContentScaleForWindow;
     auto getContentScaleForMonitor = &ImGui::Backend::Glfw::GetContentScaleForMonitor;
+    auto getFramebufferSize = &ImGui::Backend::Glfw::GetFramebufferSize;
     auto getError = &ImGui::Backend::Glfw::GetError;
 
     EXPECT_EQ(window, nullptr);
@@ -27,18 +28,25 @@ TEST(ImGuiGlfwBackendModuleTest, ExposesPlatformApi) {
     EXPECT_NE(restoreCallbacks, nullptr);
     EXPECT_NE(getContentScaleForWindow, nullptr);
     EXPECT_NE(getContentScaleForMonitor, nullptr);
+    EXPECT_NE(getFramebufferSize, nullptr);
     EXPECT_NE(getError, nullptr);
 }
 
 TEST(ImGuiOpenGL3BackendModuleTest, ExposesRendererApi) {
     auto init = &ImGui::Backend::OpenGL3::Init;
     auto shutdown = &ImGui::Backend::OpenGL3::Shutdown;
     auto newFrame = &ImGui::Backend::OpenGL3::NewFrame;
+    auto viewport = &ImGui::Backend::OpenGL3::Viewport;
+    auto clearColor = &ImGui::Backend::OpenGL3::ClearColor;
+    auto clearColorBuffer = &ImGui::Backend::OpenGL3::ClearColorBuffer;
     auto renderDrawData = &ImGui::Backend::OpenGL3::RenderDrawData;
 
     EXPECT_NE(init, nullptr);
     EXPECT_NE(shutdown, nullptr);
     EXPECT_NE(newFrame, nullptr);
+    EXPECT_NE(viewport, nullptr);
+    EXPECT_NE(clearColor, nullptr);
+    EXPECT_NE(clearColorBuffer, nullptr);
     EXPECT_NE(renderDrawData, nullptr);
 }
 
@@ -50,9 +58,13 @@ TEST(ImGuiGlfwOpenGL3BackendModuleTest, ExposesCombinedApi) {
     auto createWindow = &ImGui::Backend::GlfwOpenGL3::CreateWindow;
     auto destroyWindow = &ImGui::Backend::GlfwOpenGL3::DestroyWindow;
     auto makeContextCurrent = &ImGui::Backend::GlfwOpenGL3::MakeContextCurrent;
+    auto getFramebufferSize = &ImGui::Backend::GlfwOpenGL3::GetFramebufferSize;
     auto init = &ImGui::Backend::GlfwOpenGL3::Init;
     auto shutdown = &ImGui::Backend::GlfwOpenGL3::Shutdown;
     auto newFrame = &ImGui::Backend::GlfwOpenGL3::NewFrame;
+    auto viewport = &ImGui::Backend::GlfwOpenGL3::Viewport;
+    auto clearColor = &ImGui::Backend::GlfwOpenGL3::ClearColor;
+    auto clearColorBuffer = &ImGui::Backend::GlfwOpenGL3::ClearColorBuffer;
     auto renderDrawData = &ImGui::Backend::GlfwOpenGL3::RenderDrawData;
     auto getError = &ImGui::Backend::GlfwOpenGL3::GetError;
 
@@ -63,9 +75,13 @@ TEST(ImGuiGlfwOpenGL3BackendModuleTest, ExposesCombinedApi) {
     EXPECT_NE(createWindow, nullptr);
     EXPECT_NE(destroyWindow, nullptr);
     EXPECT_NE(makeContextCurrent, nullptr);
+    EXPECT_NE(getFramebufferSize, nullptr);
     EXPECT_NE(init, nullptr);
     EXPECT_NE(shutdown, nullptr);
     EXPECT_NE(newFrame, nullptr);
+    EXPECT_NE(viewport, nullptr);
+    EXPECT_NE(clearColor, nullptr);
+    EXPECT_NE(clearColorBuffer, nullptr);
     EXPECT_NE(renderDrawData, nullptr);
     EXPECT_NE(getError, nullptr);
 }