Example of rendering a a triangle under the UI

src/client/client_imgui.cpp

@@ -60,10 +60,51 @@ int main(int argc, char** argv)
 
     int height = 0, width = 0;
     ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
+
+    // Triangle example
+    // @see http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/
+    GLuint VertexArrayID;
+    glGenVertexArrays(1, &VertexArrayID);
+    glBindVertexArray(VertexArrayID);
+    GLuint vertexbuffer;
+    // An array of 3 vectors which represents 3 vertices
+    static const GLfloat g_vertex_buffer_data[] = {
+       -1.0f, -1.0f, 0.0f,
+       1.0f, -1.0f, 0.0f,
+       0.0f,  1.0f, 0.0f,
+    };
+    glGenBuffers(1, &vertexbuffer);
+    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data),
+                 g_vertex_buffer_data, GL_STATIC_DRAW);
     while(!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        // Process input.
 
+       // @TODO Game tick
+
+
+       // Clear GL buffers
+       glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
+       glClear(GL_COLOR_BUFFER_BIT);
+
+       // Render game geometries
+       // @see https://blog.conan.io/2019/06/26/An-introduction-to-the-Dear-ImGui-library.html
+       // 1st attribute buffer : vertices
+       glEnableVertexAttribArray(0);
+       glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
+       glVertexAttribPointer(
+          0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
+          3,                  // size
+          GL_FLOAT,           // type
+          GL_FALSE,           // normalized?
+          0,                  // stride
+          (void*)0            // array buffer offset
+          );
+       // Draw the triangle !
+       glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
+       glDisableVertexAttribArray(0);
+
        // Start the Dear ImGui frame
        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplGlfw_NewFrame();
@@ -89,16 +130,15 @@ int main(int argc, char** argv)
           ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
           ImGui::End();
        }
-       // @TODO Game tick
 
-       // Rendering
+       // Finalise rendering
        ImGui::Render();
+       ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+
+       // Swap buffers
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
-       glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
-       glClear(GL_COLOR_BUFFER_BIT);
-       ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
        glfwSwapBuffers(window);
     }