Examples: Emscripten+WebGPU: slightly refactor like other Emscripten compatible Desktop examples, as aiming to make this suppot desktop eventually.

Also aimed at reducing diff for https://github.com/ocornut/imgui/pull/7132 tho this will lead in conflict.

examples/example_emscripten_wgpu/README.md

@@ -6,7 +6,7 @@
 
 - You may also refer to our [Continuous Integration setup](https://github.com/ocornut/imgui/tree/master/.github/workflows) for Emscripten setup.
 
-- Then build using `make` while in the `example_emscripten_wgpu/` directory.
+- Then build using `make -f Makefile.emscripten` while in the `example_emscripten_wgpu/` directory.
 
 - Requires recent Emscripten as WGPU is still a work-in-progress API.
 

examples/example_emscripten_wgpu/main.cpp

@@ -11,13 +11,20 @@
 #include "imgui_impl_glfw.h"
 #include "imgui_impl_wgpu.h"
 #include <stdio.h>
+#ifdef __EMSCRIPTEN__
 #include <emscripten.h>
 #include <emscripten/html5.h>
 #include <emscripten/html5_webgpu.h>
+#endif
 #include <GLFW/glfw3.h>
 #include <webgpu/webgpu.h>
 #include <webgpu/webgpu_cpp.h>
 
+// This example can also compile and run with Emscripten! See 'Makefile.emscripten' for details.
+#ifdef __EMSCRIPTEN__
+#include "../libs/emscripten/emscripten_mainloop_stub.h"
+#endif
+
 // Global WebGPU required states
 static WGPUDevice        wgpu_device = nullptr;
 static WGPUSurface       wgpu_surface = nullptr;
@@ -27,15 +34,32 @@ static int               wgpu_swap_chain_width = 0;
 static int               wgpu_swap_chain_height = 0;
 
 // Forward declarations
-static void MainLoopStep(void* window);
 static bool InitWGPU();
-static void print_glfw_error(int error, const char* description);
+static void CreateSwapChain(int width, int height);
-static void print_wgpu_error(WGPUErrorType error_type, const char* message, void*);
+
+static void glfw_error_callback(int error, const char* description)
+{
+    printf("GLFW Error %d: %s\n", error, description);
+}
+
+static void wgpu_error_callback(WGPUErrorType error_type, const char* message, void*)
+{
+    const char* error_type_lbl = "";
+    switch (error_type)
+    {
+    case WGPUErrorType_Validation:  error_type_lbl = "Validation"; break;
+    case WGPUErrorType_OutOfMemory: error_type_lbl = "Out of memory"; break;
+    case WGPUErrorType_Unknown:     error_type_lbl = "Unknown"; break;
+    case WGPUErrorType_DeviceLost:  error_type_lbl = "Device lost"; break;
+    default:                        error_type_lbl = "Unknown";
+    }
+    printf("%s error: %s\n", error_type_lbl, message);
+}
 
 // Main code
 int main(int, char**)
 {
-    glfwSetErrorCallback(print_glfw_error);
+    glfwSetErrorCallback(glfw_error_callback);
     if (!glfwInit())
         return 1;
 
@@ -43,11 +67,8 @@ int main(int, char**)
     // This needs to be done explicitly later.
     glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
     GLFWwindow* window = glfwCreateWindow(1280, 720, "Dear ImGui GLFW+WebGPU example", nullptr, nullptr);
-    if (!window)
+    if (window == nullptr)
-    {
-        glfwTerminate();
         return 1;
-    }
 
     // Initialize the WebGPU environment
     if (!InitWGPU())
@@ -66,17 +87,15 @@ int main(int, char**)
     io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls
     io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;      // Enable Gamepad Controls
 
-    // For an Emscripten build we are disabling file-system access, so let's not attempt to do a fopen() of the imgui.ini file.
-    // You may manually call LoadIniSettingsFromMemory() to load settings from your own storage.
-    io.IniFilename = nullptr;
-
     // Setup Dear ImGui style
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsLight();
 
     // Setup Platform/Renderer backends
     ImGui_ImplGlfw_InitForOther(window, true);
+#ifdef __EMSCRIPTEN__
     ImGui_ImplGlfw_InstallEmscriptenCanvasResizeCallback("#canvas");
+#endif
     ImGui_ImplWGPU_Init(wgpu_device, 3, wgpu_preferred_fmt, WGPUTextureFormat_Undefined);
 
     // Load Fonts
@@ -99,64 +118,35 @@ int main(int, char**)
     //IM_ASSERT(font != nullptr);
 #endif
 
-    // This function will directly return and exit the main function.
+    // Our state
-    // Make sure that no required objects get cleaned up.
+    bool show_demo_window = true;
-    // This way we can use the browsers 'requestAnimationFrame' to control the rendering.
+    bool show_another_window = false;
-    emscripten_set_main_loop_arg(MainLoopStep, window, 0, false);
+    ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
-
-    return 0;
-}
-
-static bool InitWGPU()
-{
-    wgpu_device = emscripten_webgpu_get_device();
-    if (!wgpu_device)
-        return false;
-
-    wgpuDeviceSetUncapturedErrorCallback(wgpu_device, print_wgpu_error, nullptr);
-
-    // Use C++ wrapper due to misbehavior in Emscripten.
-    // Some offset computation for wgpuInstanceCreateSurface in JavaScript
-    // seem to be inline with struct alignments in the C++ structure
-    wgpu::SurfaceDescriptorFromCanvasHTMLSelector html_surface_desc = {};
-    html_surface_desc.selector = "#canvas";
-
-    wgpu::SurfaceDescriptor surface_desc = {};
-    surface_desc.nextInChain = &html_surface_desc;
-
-    wgpu::Instance instance = wgpuCreateInstance(nullptr);
-    wgpu::Surface surface = instance.CreateSurface(&surface_desc);
-    wgpu::Adapter adapter = {};
-    wgpu_preferred_fmt = (WGPUTextureFormat)surface.GetPreferredFormat(adapter);
-    wgpu_surface = surface.MoveToCHandle();
-
-    return true;
-}
 
-static void MainLoopStep(void* window)
+    // Main loop
+#ifdef __EMSCRIPTEN__
+    // For an Emscripten build we are disabling file-system access, so let's not attempt to do a fopen() of the imgui.ini file.
+    // You may manually call LoadIniSettingsFromMemory() to load settings from your own storage.
+    io.IniFilename = nullptr;
+    EMSCRIPTEN_MAINLOOP_BEGIN
+#else
+    while (!glfwWindowShouldClose(window))
+#endif
     {
-    ImGuiIO& io = ImGui::GetIO();
+        // Poll and handle events (inputs, window resize, etc.)
-
+        // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
+        // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
+        // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
+        // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
         glfwPollEvents();
 
+        // React to changes in screen size
         int width, height;
         glfwGetFramebufferSize((GLFWwindow*)window, &width, &height);
-
-    // React to changes in screen size
         if (width != wgpu_swap_chain_width && height != wgpu_swap_chain_height)
         {
             ImGui_ImplWGPU_InvalidateDeviceObjects();
-        if (wgpu_swap_chain)
+            CreateSwapChain(width, height);
-            wgpuSwapChainRelease(wgpu_swap_chain);
-        wgpu_swap_chain_width = width;
-        wgpu_swap_chain_height = height;
-        WGPUSwapChainDescriptor swap_chain_desc = {};
-        swap_chain_desc.usage = WGPUTextureUsage_RenderAttachment;
-        swap_chain_desc.format = wgpu_preferred_fmt;
-        swap_chain_desc.width = width;
-        swap_chain_desc.height = height;
-        swap_chain_desc.presentMode = WGPUPresentMode_Fifo;
-        wgpu_swap_chain = wgpuDeviceCreateSwapChain(wgpu_device, wgpu_surface, &swap_chain_desc);
             ImGui_ImplWGPU_CreateDeviceObjects();
         }
 
@@ -165,12 +155,6 @@ static void MainLoopStep(void* window)
         ImGui_ImplGlfw_NewFrame();
         ImGui::NewFrame();
 
-    // Our state
-    // (we use static, which essentially makes the variable globals, as a convenience to keep the example code easy to follow)
-    static bool show_demo_window = true;
-    static bool show_another_window = false;
-    static ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);
-
         // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
         if (show_demo_window)
             ImGui::ShowDemoWindow(&show_demo_window);
@@ -216,6 +200,7 @@ static void MainLoopStep(void* window)
         color_attachments.storeOp = WGPUStoreOp_Store;
         color_attachments.clearValue = { clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w };
         color_attachments.view = wgpuSwapChainGetCurrentTextureView(wgpu_swap_chain);
+
         WGPURenderPassDescriptor render_pass_desc = {};
         render_pass_desc.colorAttachmentCount = 1;
         render_pass_desc.colorAttachments = &color_attachments;
@@ -233,22 +218,58 @@ static void MainLoopStep(void* window)
         WGPUQueue queue = wgpuDeviceGetQueue(wgpu_device);
         wgpuQueueSubmit(queue, 1, &cmd_buffer);
     }
+#ifdef __EMSCRIPTEN__
+    EMSCRIPTEN_MAINLOOP_END;
+#endif
 
-static void print_glfw_error(int error, const char* description)
+    // Cleanup
-{
+    ImGui_ImplWGPU_Shutdown();
-    printf("GLFW Error %d: %s\n", error, description);
+    ImGui_ImplGlfw_Shutdown();
+    ImGui::DestroyContext();
+
+    glfwDestroyWindow(window);
+    glfwTerminate();
+
+    return 0;
 }
 
-static void print_wgpu_error(WGPUErrorType error_type, const char* message, void*)
+static bool InitWGPU()
-{
-    const char* error_type_lbl = "";
-    switch (error_type)
 {
-    case WGPUErrorType_Validation:  error_type_lbl = "Validation"; break;
+    wgpu_device = emscripten_webgpu_get_device();
-    case WGPUErrorType_OutOfMemory: error_type_lbl = "Out of memory"; break;
+    if (!wgpu_device)
-    case WGPUErrorType_Unknown:     error_type_lbl = "Unknown"; break;
+        return false;
-    case WGPUErrorType_DeviceLost:  error_type_lbl = "Device lost"; break;
+
-    default:                        error_type_lbl = "Unknown";
+    wgpuDeviceSetUncapturedErrorCallback(wgpu_device, wgpu_error_callback, nullptr);
+
+    // Use C++ wrapper due to misbehavior in Emscripten.
+    // Some offset computation for wgpuInstanceCreateSurface in JavaScript
+    // seem to be inline with struct alignments in the C++ structure
+    wgpu::SurfaceDescriptorFromCanvasHTMLSelector html_surface_desc = {};
+    html_surface_desc.selector = "#canvas";
+
+    wgpu::SurfaceDescriptor surface_desc = {};
+    surface_desc.nextInChain = &html_surface_desc;
+
+    wgpu::Instance instance = wgpuCreateInstance(nullptr);
+    wgpu::Surface surface = instance.CreateSurface(&surface_desc);
+    wgpu::Adapter adapter = {};
+    wgpu_preferred_fmt = (WGPUTextureFormat)surface.GetPreferredFormat(adapter);
+    wgpu_surface = surface.MoveToCHandle();
+
+    return true;
 }
-    printf("%s error: %s\n", error_type_lbl, message);
+
+static void CreateSwapChain(int width, int height)
+{
+    if (wgpu_swap_chain)
+        wgpuSwapChainRelease(wgpu_swap_chain);
+    wgpu_swap_chain_width = width;
+    wgpu_swap_chain_height = height;
+    WGPUSwapChainDescriptor swap_chain_desc = {};
+    swap_chain_desc.usage = WGPUTextureUsage_RenderAttachment;
+    swap_chain_desc.format = wgpu_preferred_fmt;
+    swap_chain_desc.width = width;
+    swap_chain_desc.height = height;
+    swap_chain_desc.presentMode = WGPUPresentMode_Fifo;
+    wgpu_swap_chain = wgpuDeviceCreateSwapChain(wgpu_device, wgpu_surface, &swap_chain_desc);
 }