Start implementing glClear

Currently, because both SurfaceWgpu::getAttachmentRenderTarget() and
TextureWgpu::getAttachmentRenderTarget() are unimplemented, there is
no actual RenderTargetWgpu in the RenderTargetCache to clear.

Bug: angleproject:8582
Change-Id: I9ad33c57d533d81178d7d2a802d35b106ece5848
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5388076
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Liza Burakova <liza@chromium.org>
Commit-Queue: Matthew Denton <mpdenton@chromium.org>

src/libANGLE/renderer/wgpu/FramebufferWgpu.cpp

@@ -47,6 +47,40 @@ angle::Result FramebufferWgpu::invalidateSub(const gl::Context *context,
 
 angle::Result FramebufferWgpu::clear(const gl::Context *context, GLbitfield mask)
 {
+    bool clearColor   = IsMaskFlagSet(mask, static_cast<GLbitfield>(GL_COLOR_BUFFER_BIT));
+    bool clearDepth   = IsMaskFlagSet(mask, static_cast<GLbitfield>(GL_DEPTH_BUFFER_BIT));
+    bool clearStencil = IsMaskFlagSet(mask, static_cast<GLbitfield>(GL_STENCIL_BUFFER_BIT));
+    // TODO(anglebug.com/8582): support clearing depth and stencil buffers.
+    ASSERT(!clearDepth && !clearStencil && clearColor);
+
+    ContextWgpu *contextWgpu   = GetImplAs<ContextWgpu>(context);
+    gl::ColorF colorClearValue = context->getState().getColorClearValue();
+
+    std::vector<wgpu::RenderPassColorAttachment> colorAttachments(
+        mState.getEnabledDrawBuffers().count());
+    for (size_t enabledDrawBuffer : mState.getEnabledDrawBuffers())
+    {
+        wgpu::RenderPassColorAttachment colorAttachment;
+        colorAttachment.view =
+            mRenderTargetCache.getColorDraw(mState, enabledDrawBuffer)->getTexture();
+        colorAttachment.depthSlice   = wgpu::kDepthSliceUndefined;
+        colorAttachment.loadOp       = wgpu::LoadOp::Clear;
+        colorAttachment.storeOp      = wgpu::StoreOp::Store;
+        colorAttachment.clearValue.r = colorClearValue.red;
+        colorAttachment.clearValue.g = colorClearValue.green;
+        colorAttachment.clearValue.b = colorClearValue.blue;
+        colorAttachment.clearValue.a = colorClearValue.alpha;
+        colorAttachments.push_back(colorAttachment);
+    }
+
+    wgpu::RenderPassDescriptor renderPassDesc;
+    renderPassDesc.colorAttachmentCount = colorAttachments.size();
+    renderPassDesc.colorAttachments     = colorAttachments.data();
+
+    // TODO(anglebug.com/8582): optimize this implementation.
+    ANGLE_TRY(contextWgpu->ensureRenderPassStarted(renderPassDesc));
+    ANGLE_TRY(contextWgpu->endRenderPass(webgpu::RenderPassClosureReason::NewRenderPass));
+    ANGLE_TRY(contextWgpu->flush());
     return angle::Result::Continue;
 }
 

src/libANGLE/renderer/wgpu/SurfaceWgpu.cpp

@@ -112,4 +112,14 @@ egl::Error SurfaceWgpu::detachFromFramebuffer(const gl::Context *context,
     return egl::NoError();
 }
 
+angle::Result SurfaceWgpu::getAttachmentRenderTarget(const gl::Context *context,
+                                                     GLenum binding,
+                                                     const gl::ImageIndex &imageIndex,
+                                                     GLsizei samples,
+                                                     FramebufferAttachmentRenderTarget **rtOut)
+{
+    UNIMPLEMENTED();
+    return angle::Result::Stop;
+}
+
 }  // namespace rx

src/libANGLE/renderer/wgpu/SurfaceWgpu.h

@@ -52,6 +52,12 @@ class SurfaceWgpu : public SurfaceImpl
                                    gl::Framebuffer *framebuffer) override;
     egl::Error detachFromFramebuffer(const gl::Context *context,
                                      gl::Framebuffer *framebuffer) override;
+
+    angle::Result getAttachmentRenderTarget(const gl::Context *context,
+                                            GLenum binding,
+                                            const gl::ImageIndex &imageIndex,
+                                            GLsizei samples,
+                                            FramebufferAttachmentRenderTarget **rtOut) override;
 };
 
 }  // namespace rx