ImGui Draw Compare

This repo has code that's used to compare ImGui draw data for changes in order to minimize unnecessary re-rendering.

ImDrawCmpCache::Compare() compares cached ImDrawVert/ImDrawIdx data from an ImGui context's ImDrawData to determine whether the GUI has actually changed. It returns true if no changes occurred. Essentially, Compare() is running memcmp's between the old and new vertex/index data for the UI.

The purpose is to reduce reduce idle GPU load that occurs otherwise.

Here's a simple reference:

ImDrawCmpCache draw_cache;
while (!glfwWindowShouldClose(window)) {
    glfwPollEvents();
    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplGlfw_NewFrame();
    ImGui::NewFrame();
    ImGui::ShowDemoWindow();
    ImGui::Render();
    if (draw_cache.Compare(ImGui::GetDrawData())) continue; // Skip rendering if no changes.
    glClearColor(.1, .1, .1, 1);
    glClear(GL_COLOR_BUFFER_BIT);
    ImGui_ImplOpenGL3_RenderDrawData(draw_data); // GUI is literally drawn here.
    glfwSwapBuffers(window);
}

There's a full implementation example in this repo.