ImGui Integration

Update Swapchain to expose its image format:

[[nodiscard]] auto get_format() const -> vk::Format {
  return m_ci.imageFormat;
}

class App can now store a std::optional<DearImGui> member and add/call its create function:

void App::create_imgui() {
  auto const imgui_ci = DearImGui::CreateInfo{
    .window = m_window.get(),
    .api_version = vk_version_v,
    .instance = *m_instance,
    .physical_device = m_gpu.device,
    .queue_family = m_gpu.queue_family,
    .device = *m_device,
    .queue = m_queue,
    .color_format = m_swapchain->get_format(),
    .samples = vk::SampleCountFlagBits::e1,
  };
  m_imgui.emplace(imgui_ci);
}

Start a new ImGui frame after resetting the render fence, and show the demo window:

m_device->resetFences(*render_sync.drawn);
m_imgui->new_frame();

// ...
command_buffer.beginRendering(rendering_info);
ImGui::ShowDemoWindow();
// draw stuff here.
command_buffer.endRendering();

ImGui doesn't draw anything here (the actual draw command requires the Command Buffer), it's just a good customization point for all higher level logic.

We use a separate render pass for Dear ImGui, again for isolation, and to enable us to change the main render pass later, eg by adding a depth buffer attachment (DearImGui is setup assuming its render pass will only use a single color attachment).

m_imgui->end_frame();
// we don't want to clear the image again, instead load it intact after the
// previous pass.
color_attachment.setLoadOp(vk::AttachmentLoadOp::eLoad);
rendering_info.setColorAttachments(color_attachment)
  .setPDepthAttachment(nullptr);
command_buffer.beginRendering(rendering_info);
m_imgui->render(command_buffer);
command_buffer.endRendering();