Examples: Emscripten+webgpu: Fixed WGPUInstance creation process + use preferred framebuffer format. (#6640, #6748)

docs/CHANGELOG.txt

@@ -72,6 +72,8 @@ Other changes:
 - Backends: SDL2,SDL3: added ImGui_ImplSDL2_InitForOther()/ImGui_ImplSDL3_InitForOther()
   for consistency (matching GLFW backend) and as most initialization paths don't actually
   need to care about rendering backend.
+- Examples: Emscripten+WebGPU: Fixed WGPUInstance creation process + use preferred
+  framebuffer format. (#6640, #6748) [@smileorigin]
 
 
 -----------------------------------------------------------------------

examples/example_emscripten_wgpu/main.cpp

@@ -17,6 +17,7 @@
 // Global WebGPU required states
 static WGPUDevice        wgpu_device = nullptr;
 static WGPUSurface       wgpu_surface = nullptr;
+static WGPUTextureFormat wgpu_preferred_fmt = WGPUTextureFormat_RGBA8Unorm;
 static WGPUSwapChain     wgpu_swap_chain = nullptr;
 static int               wgpu_swap_chain_width = 0;
 static int               wgpu_swap_chain_height = 0;
@@ -71,7 +72,7 @@ int main(int, char**)
 
     // Setup Platform/Renderer backends
     ImGui_ImplGlfw_InitForOther(window, true);
-    ImGui_ImplWGPU_Init(wgpu_device, 3, WGPUTextureFormat_RGBA8Unorm, WGPUTextureFormat_Undefined);
+    ImGui_ImplWGPU_Init(wgpu_device, 3, wgpu_preferred_fmt, WGPUTextureFormat_Undefined);
 
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
@@ -118,9 +119,11 @@ static bool InitWGPU()
     wgpu::SurfaceDescriptor surface_desc = {};
     surface_desc.nextInChain = &html_surface_desc;
 
-    // Use 'null' instance
-    wgpu::Instance instance = {};
-    wgpu_surface = instance.CreateSurface(&surface_desc).Release();
+    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.Release();
 
     return true;
 }
@@ -144,7 +147,7 @@ static void MainLoopStep(void* window)
         wgpu_swap_chain_height = height;
         WGPUSwapChainDescriptor swap_chain_desc = {};
         swap_chain_desc.usage = WGPUTextureUsage_RenderAttachment;
-        swap_chain_desc.format = WGPUTextureFormat_RGBA8Unorm;
+        swap_chain_desc.format = wgpu_preferred_fmt;
         swap_chain_desc.width = width;
         swap_chain_desc.height = height;
         swap_chain_desc.presentMode = WGPUPresentMode_Fifo;