WebGPU backend fix to deal with Dawn change

[GrigoryGraborenko]

Version/Branch of Dear ImGui:

Version 1.9.0, Branch: master

Back-ends:

imgui_impl_wgpu.cpp

Compiler, OS:

Windows 10 + MSVC 2022

Full config/build information:

Dear ImGui 1.90 WIP (18993)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201703
define: _WIN32
define: _WIN64
define: _MSC_VER=1937
define: _MSVC_LANG=201703
--------------------------------
io.BackendPlatformName: imgui_impl_sdl2
io.BackendRendererName: imgui_impl_webgpu
io.ConfigFlags: 0x00000000
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x0000000E
 HasMouseCursors
 HasSetMousePos
 RendererHasVtxOffset
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1280.00,720.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 0.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00

Details:

Recently there was a change in Dawn's native WebGPU implementation where they no longer gave sensible defaults to stencil operations for render pipelines:
https://dawn.googlesource.com/dawn/+/628a1eb2a720bef3dd25bf352094c76a74514efe%5E%21/#F1

When validating the render pipeline, this condition gets triggered:

DAWN_INVALID_IF(!format->HasStencil() && StencilTestEnabled(descriptor),
                "Depth stencil format (%s) doesn't have stencil aspect while stencil "
                "test or stencil write is enabled.",
                descriptor->format);

which calls this function:

bool StencilTestEnabled(const DepthStencilState* depthStencil) {
    return depthStencil->stencilBack.compare != wgpu::CompareFunction::Always ||
           depthStencil->stencilBack.failOp != wgpu::StencilOperation::Keep ||
           depthStencil->stencilBack.depthFailOp != wgpu::StencilOperation::Keep ||
           depthStencil->stencilBack.passOp != wgpu::StencilOperation::Keep ||
           depthStencil->stencilFront.compare != wgpu::CompareFunction::Always ||
           depthStencil->stencilFront.failOp != wgpu::StencilOperation::Keep ||
           depthStencil->stencilFront.depthFailOp != wgpu::StencilOperation::Keep ||
           depthStencil->stencilFront.passOp != wgpu::StencilOperation::Keep;
}

Those wgpu::StencilOperation::Keep are actually 1 not 0 so the defaults immediately fail validation if you don't set them.

In imgui_impl_wgpu.cpp on line 651 you create a WGPUDepthStencilState and set the compare functions:

    // Create depth-stencil State
    WGPUDepthStencilState depth_stencil_state = {};
    depth_stencil_state.format = bd->depthStencilFormat;
    depth_stencil_state.depthWriteEnabled = false;
    depth_stencil_state.depthCompare = WGPUCompareFunction_Always;
    depth_stencil_state.stencilFront.compare = WGPUCompareFunction_Always;
    depth_stencil_state.stencilBack.compare = WGPUCompareFunction_Always;

May I humbly request we add these lines below:

	depth_stencil_state.stencilFront.failOp = WGPUStencilOperation_Keep;
	depth_stencil_state.stencilFront.depthFailOp = WGPUStencilOperation_Keep;
	depth_stencil_state.stencilFront.passOp = WGPUStencilOperation_Keep;
	depth_stencil_state.stencilBack.failOp = WGPUStencilOperation_Keep;
	depth_stencil_state.stencilBack.depthFailOp = WGPUStencilOperation_Keep;
	depth_stencil_state.stencilBack.passOp = WGPUStencilOperation_Keep;

I was able to confirm this sets the expected defaults and passes pipeline validation.

Screenshots/Video:

No response

Minimal, Complete and Verifiable Example code:

No response

[ocornut]

Thank you Grigory for your careful and researched issue!
I have pushed your suggested fix as 03417cc