Backends: WebGPU: Align buffer sizes upon creation. (#6188)

Amend from original pr to use a macro.

backends/imgui_impl_wgpu.cpp

@@ -13,6 +13,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2023-04-11: Align buffer sizes.
 //  2023-04-11: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
 //  2023-01-25: Revert automatic pipeline layout generation (see https://github.com/gpuweb/gpuweb/issues/2470)
 //  2022-11-24: Fixed validation error with default depth buffer settings.
@@ -33,6 +34,7 @@
 
 // Dear ImGui prototypes from imgui_internal.h
 extern ImGuiID ImHashData(const void* data_p, size_t data_size, ImU32 seed = 0);
+#define MEMALIGN(_SIZE,_ALIGN)        (((_SIZE) + ((_ALIGN) - 1)) & ~((_ALIGN) - 1))    // Memory align (copied from IM_ALIGN() macro).
 
 // WebGPU data
 struct RenderResources
@@ -370,7 +372,7 @@ void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURenderPassEncoder
             nullptr,
             "Dear ImGui Vertex buffer",
             WGPUBufferUsage_CopyDst | WGPUBufferUsage_Vertex,
-            fr->VertexBufferSize * sizeof(ImDrawVert),
+            MEMALIGN(fr->VertexBufferSize * sizeof(ImDrawVert), 4),
             false
         };
         fr->VertexBuffer = wgpuDeviceCreateBuffer(bd->wgpuDevice, &vb_desc);
@@ -394,7 +396,7 @@ void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURenderPassEncoder
             nullptr,
             "Dear ImGui Index buffer",
             WGPUBufferUsage_CopyDst | WGPUBufferUsage_Index,
-            fr->IndexBufferSize * sizeof(ImDrawIdx),
+            MEMALIGN(fr->IndexBufferSize * sizeof(ImDrawIdx), 4),
             false
         };
         fr->IndexBuffer = wgpuDeviceCreateBuffer(bd->wgpuDevice, &ib_desc);
@@ -415,8 +417,8 @@ void ImGui_ImplWGPU_RenderDrawData(ImDrawData* draw_data, WGPURenderPassEncoder
         vtx_dst += cmd_list->VtxBuffer.Size;
         idx_dst += cmd_list->IdxBuffer.Size;
     }
-    int64_t vb_write_size = ((char*)vtx_dst - (char*)fr->VertexBufferHost + 3) & ~3;
-    int64_t ib_write_size = ((char*)idx_dst - (char*)fr->IndexBufferHost  + 3) & ~3;
+    int64_t vb_write_size = MEMALIGN((char*)vtx_dst - (char*)fr->VertexBufferHost, 4);
+    int64_t ib_write_size = MEMALIGN((char*)idx_dst - (char*)fr->IndexBufferHost, 4);
     wgpuQueueWriteBuffer(bd->defaultQueue, fr->VertexBuffer, 0, fr->VertexBufferHost, vb_write_size);
     wgpuQueueWriteBuffer(bd->defaultQueue, fr->IndexBuffer,  0, fr->IndexBufferHost,  ib_write_size);
 
@@ -553,7 +555,7 @@ static void ImGui_ImplWGPU_CreateUniformBuffer()
         nullptr,
         "Dear ImGui Uniform buffer",
         WGPUBufferUsage_CopyDst | WGPUBufferUsage_Uniform,
-        sizeof(Uniforms),
+        MEMALIGN(sizeof(Uniforms), 4),
         false
     };
     bd->renderResources.Uniforms = wgpuDeviceCreateBuffer(bd->wgpuDevice, &ub_desc);

docs/CHANGELOG.txt

@@ -90,6 +90,7 @@ Other changes:
   (#6315) [@PathogenDavid]
 - Backends: OSX: Added support for io.AddMouseSourceEvent() to discriminate Mouse/Pen.
   (#6314) [@PathogenDavid]
+- Backends: WebGPU: Align buffers. (#6188) [@eliemichel]
 - Backends: WebGPU: Reorganized to store data in io.BackendRendererUserData like other backends.
 - Examples: Windows: Added 'misc/debuggers/imgui.natstepfilter' file to all Visual Studio projects,
   now that VS 2022 17.6 Preview 2 support adding Debug Step Filter spec files into projects.