xo-imgui: support dynamic vsync_enabled setting + demo in ex4

xo-imgui/example/ex4/DrawState.cpp

@@ -741,7 +741,7 @@ DrawState::draw_gc_state(const AppState & app_state,
     /* TODO: does this reset coord space? */
     ImRect alloc_rect;
     {
-        ImGui::BeginChild("top pane", ImVec2(0, 105), ImGuiChildFlags_Border | ImGuiChildFlags_ResizeY);
+        ImGui::BeginChild("top pane", ImVec2(0, 200), ImGuiChildFlags_Border | ImGuiChildFlags_ResizeY);
 
         alloc_rect = ImRect(canvas_rect.top_left() + ImGui::GetWindowContentRegionMin(),
                             canvas_rect.top_left() + ImGui::GetWindowContentRegionMax());
@@ -817,7 +817,7 @@ DrawState::draw_gc_state(const AppState & app_state,
          ImGui::EndChild();
     }
 
-    ImGui::Text("placeholder text");
+    //ImGui::Text("placeholder text"); // appears below history_rect
 
     /* BeginChild() again ? */
 

xo-imgui/example/ex4/DrawState.hpp

@@ -85,6 +85,8 @@ struct DrawState {
 public:
     /** when true display imgui demo window **/
     bool show_demo_window_ = false;
+    /** whether vsync feature enabled (throttle to ~60 fps) **/
+    bool vsync_enabled_ = true;
 
     draw_state_type state_type_ = draw_state_type::alloc;
 

xo-imgui/example/ex4/imgui_ex4.cpp

@@ -80,7 +80,7 @@ namespace {
         *p_f = 0.0f;
         *p_counter = 0;
 
-        return [p_app_state, p_draw_state, p_f, p_counter](ImGuiContext * imgui_cx)
+        return [p_app_state, p_draw_state, p_f, p_counter](VulkanApp * vulkan_app, ImGuiContext * imgui_cx)
             {
                 scope log(XO_DEBUG(false));
 
@@ -108,6 +108,19 @@ namespace {
                 ImGui::End();
 # endif
 
+                // 0. main menubar
+                if (ImGui::BeginMainMenuBar()) {
+                    if (ImGui::BeginMenu("View")) {
+                        bool x = vulkan_app->vsync_enabled_flag();
+
+                        if (ImGui::MenuItem("vsync", nullptr, &x)) {
+                            vulkan_app->update_vsync_enabled(x);
+                        }
+                        ImGui::EndMenu();
+                    }
+                    ImGui::EndMainMenuBar();
+                }
+
                 // 1. create a simple ImGui window
                 ImGui::Begin("Hello, Vulkan + SDL2!");
                 ImGui::Text("This is a minimal ImGui + Vulkan + SDL2 example!");

xo-imgui/include/xo/imgui/VulkanApp.hpp

@@ -13,7 +13,7 @@
 
 class VulkanApp {
 public:
-    using ImguiDrawFn = std::function<ImDrawData * (ImGuiContext *)>;
+    using ImguiDrawFn = std::function<ImDrawData * (VulkanApp *, ImGuiContext *)>;
 
 public:
     /* create single-window vulkan application;
@@ -21,9 +21,17 @@ public:
      */
     VulkanApp(ImguiDrawFn fn);
 
+    bool vsync_enabled_flag() const { return vsync_enabled_flag_; }
+
+    /* update vsync enabled (will recreate xswapchain at next opportunity)
+     */
+    void update_vsync_enabled(bool flag);
+
     /* run application; borrows calling thread for event loop,
      * until application exit.
      * Invoke load_fonts once imgui context established
+     * @ref vsync_enabled_flag_. true for VK_PRESENT_MODE_FIFO_KHR;
+     * false for VK_PRESENT_MODE_IMMEDIATE_KHR
      */
     void run(std::function<void (ImGuiContext *)> load_fonts);
 
@@ -47,7 +55,10 @@ private:
      */
     void init_sdl_window();
 
-    /* setup vulkan state. swapchain, command buffers etc */
+    /* setup vulkan state. swapchain, command buffers etc
+     * @ref vsync_enabled_flag_. true for VK_PRESENT_MODE_FIFO_KHR;
+     * false for VK_PRESENT_MODE_IMMEDIATE_KHR
+     */
     void init_vulkan();
 
     /* create vulkan instance.
@@ -74,6 +85,8 @@ private:
     /* populates @ref swapchain_, @ref swapchain_images_,
      * @ref swapchain_image_views_, @ref framebuffers_.
      * Also $ref render_pass_ iff @p create_render_pass_flag
+     * @ref vsync_enabled_flag_. true for VK_PRESENT_MODE_FIFO_KHR;
+     * false for VK_PRESENT_MODE_IMMEDIATE_KHR
      */
     void create_xswapchain(bool create_render_pass_flag);
 
@@ -175,6 +188,10 @@ private:
 
     /* abstraction for presentation area (?) */
     VkSurfaceKHR surface_;
+    /* true -> VK_PRESENT_MODE_FIFO_KHR
+     * false -> VK_PRESENT_MODE_IMMEDIATE_KHR
+     */
+    bool vsync_enabled_flag_ = true;
 
     /* physical device (graphics card) */
     VkPhysicalDevice physical_device_;
@@ -210,10 +227,14 @@ private:
     const size_t c_max_frames_in_flight = 2;
     /* true iff @ref setup has been called */
     bool setup_flag_ = false;
-    /* true when window resize behavior detected,
-     * until swapchain in consistent state.
+    /* true if xswapchain is out-of-date.
+     * reset when xswapchain recreated (and therefore in consistent state).
+     *
+     * Triggered by:
+     * - window resize
+     * - vsync toggled
      */
-    bool framebuffer_resized_flag_ = false;
+    bool xswapchain_recreate_flag_ = false;
     bool quit_flag_ = false;
 
     /** draw imgui **/

xo-imgui/src/imgui/VulkanApp.cpp

@@ -216,7 +216,7 @@ VulkanApp::create_swapchain()
     create_info.imageSharingMode = VK_SHARING_MODE_EXCLUSIVE;
     create_info.preTransform = capabilities.currentTransform;
     create_info.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
-    create_info.presentMode = VK_PRESENT_MODE_FIFO_KHR;
+    create_info.presentMode = (vsync_enabled_flag_ ? VK_PRESENT_MODE_FIFO_KHR : VK_PRESENT_MODE_IMMEDIATE_KHR);
     create_info.clipped = VK_TRUE;
 
     if (vkCreateSwapchainKHR(device_, &create_info, nullptr, &(this->swapchain_)) != VK_SUCCESS) {
@@ -564,7 +564,7 @@ VulkanApp::draw_frame()
 
     result = vkQueuePresentKHR(graphics_queue_, &presentInfo);
 
-    if (framebuffer_resized_flag_)
+    if (xswapchain_recreate_flag_)
         result = VK_ERROR_OUT_OF_DATE_KHR;
 
     switch (result) {
@@ -572,7 +572,6 @@ VulkanApp::draw_frame()
         break;
     case VK_ERROR_OUT_OF_DATE_KHR:
     case VK_SUBOPTIMAL_KHR:
-        framebuffer_resized_flag_ = false;
         this->recreate_xswapchain();
         break;
     default:
@@ -582,6 +581,12 @@ VulkanApp::draw_frame()
     this->current_frame_ = (current_frame_ + 1) % c_max_frames_in_flight;
 }
 
+void
+VulkanApp::update_vsync_enabled(bool flag) {
+    this->vsync_enabled_flag_ = flag;
+    this->xswapchain_recreate_flag_ = true;
+}
+
 void
 VulkanApp::record_command_buffer(VkCommandBuffer cmdbuf, uint32_t image_ix)
 {
@@ -633,7 +638,7 @@ VulkanApp::record_command_buffer(VkCommandBuffer cmdbuf, uint32_t image_ix)
     }
 #endif
 
-    ImDrawData * draw_data = imgui_draw_frame_(imgui_cx_); (void)draw_data;
+    ImDrawData * draw_data = imgui_draw_frame_(this, imgui_cx_);
 
     ImGui_ImplVulkan_RenderDrawData(draw_data, cmdbuf);
 
@@ -671,11 +676,14 @@ VulkanApp::recreate_xswapchain()
     // wait until device idle before cleaning up resources
     vkDeviceWaitIdle(device_);
 
+    // remember consistent swapchain state restored
+    this->xswapchain_recreate_flag_ = false;
+
     // cleanup old xswapchain
     this->cleanup_xswapchain();
 
     // create new swapchain
-    this->create_xswapchain(false);
+    this->create_xswapchain(false /*create_render_pass_flag*/);
 }
 
 void