Vulkan: Use depthClamp to clear depth where available

src/libANGLE/renderer/vulkan/FramebufferVk.cpp

@@ -2019,7 +2019,9 @@ angle::Result FramebufferVk::clearWithDraw(ContextVk *contextVk,
                                            const VkClearColorValue &clearColorValue,
                                            const VkClearDepthStencilValue &clearDepthStencilValue)
 {
-    if (clearDepth)
+    RendererVk *renderer = contextVk->getRenderer();
+
+    if (clearDepth && !renderer->getPhysicalDeviceFeatures().depthClamp)
     {
         VkClearValue clearValue;
         clearValue.depthStencil = clearDepthStencilValue;
@@ -2031,15 +2033,18 @@ angle::Result FramebufferVk::clearWithDraw(ContextVk *contextVk,
         // Force start a new render pass for the depth clear to take effect.
         // UtilsVk::clearFramebuffer may not start a new render pass if there's one already started.
         ANGLE_TRY(flushDeferredClears(contextVk, clearArea));
+
+        clearDepth = false;
     }
 
     UtilsVk::ClearFramebufferParameters params = {};
     params.clearArea                           = clearArea;
     params.colorClearValue                     = clearColorValue;
-    params.stencilClearValue = static_cast<uint8_t>(clearDepthStencilValue.stencil);
-    params.stencilMask       = stencilMask;
+    params.depthStencilClearValue              = clearDepthStencilValue;
+    params.stencilMask                         = stencilMask;
 
     params.clearColor   = true;
+    params.clearDepth   = clearDepth;
     params.clearStencil = clearStencil;
 
     const auto &colorRenderTargets = mRenderTargetCache.getColors();
@@ -2060,12 +2065,13 @@ angle::Result FramebufferVk::clearWithDraw(ContextVk *contextVk,
 
         ANGLE_TRY(contextVk->getUtils().clearFramebuffer(contextVk, this, params));
 
-        // Clear stencil only once!
+        // Clear depth/stencil only once!
+        params.clearDepth   = false;
         params.clearStencil = false;
     }
 
-    // If there was no color clear, clear stencil alone.
-    if (params.clearStencil)
+    // If there was no color clear, clear depth/stencil alone.
+    if (params.clearDepth || params.clearStencil)
     {
         params.clearColor = false;
         ANGLE_TRY(contextVk->getUtils().clearFramebuffer(contextVk, this, params));

src/libANGLE/renderer/vulkan/RendererVk.cpp

@@ -1336,6 +1336,8 @@ angle::Result RendererVk::initializeDevice(DisplayVk *displayVk, uint32_t queueF
     enabledFeatures.features.shaderClipDistance = mPhysicalDeviceFeatures.shaderClipDistance;
     // Used to support OES_sample_shading
     enabledFeatures.features.sampleRateShading = mPhysicalDeviceFeatures.sampleRateShading;
+    // Used to support depth clears through draw calls.
+    enabledFeatures.features.depthClamp = mPhysicalDeviceFeatures.depthClamp;
 
     if (!vk::CommandBuffer::ExecutesInline())
     {

src/libANGLE/renderer/vulkan/UtilsVk.cpp

@@ -1402,14 +1402,21 @@ angle::Result UtilsVk::clearFramebuffer(ContextVk *contextVk,
         ANGLE_TRY(contextVk->startRenderPass(scissoredRenderArea, &commandBuffer));
     }
 
-    if (params.clearStencil)
+    if (params.clearStencil || params.clearDepth)
     {
         vk::CommandBufferHelper *renderpassCommands;
         renderpassCommands = &contextVk->getStartedRenderPassCommands();
 
-        // Because clear is not affected by stencil test, we have to explicitly mark stencil write
-        // here.
-        renderpassCommands->onStencilAccess(vk::ResourceAccess::Write);
+        // Because clear is not affected by depth/stencil test, we have to explicitly mark
+        // depth/stencil write here.
+        if (params.clearDepth)
+        {
+            renderpassCommands->onDepthAccess(vk::ResourceAccess::Write);
+        }
+        if (params.clearStencil)
+        {
+            renderpassCommands->onStencilAccess(vk::ResourceAccess::Write);
+        }
 
         // We may have changed depth stencil access mode, so update read only depth stencil mode
         // here.
@@ -1433,11 +1440,25 @@ angle::Result UtilsVk::clearFramebuffer(ContextVk *contextVk,
     // used.
     pipelineDesc.setSubpass(contextVk->getCurrentSubpassIndex());
 
+    // Clear depth by enabling depth clamping and setting the viewport depth range to the clear
+    // value.
+    if (params.clearDepth)
+    {
+        // This path requires the depthClamp Vulkan feature.
+        ASSERT(contextVk->getRenderer()->getPhysicalDeviceFeatures().depthClamp);
+
+        pipelineDesc.setDepthTestEnabled(true);
+        pipelineDesc.setDepthWriteEnabled(true);
+        pipelineDesc.setDepthFunc(VK_COMPARE_OP_ALWAYS);
+        pipelineDesc.setDepthClampEnabled(true);
+    }
+
     // Clear stencil by enabling stencil write with the right mask.
     if (params.clearStencil)
     {
-        const uint8_t compareMask       = 0xFF;
-        const uint8_t clearStencilValue = params.stencilClearValue;
+        const uint8_t compareMask = 0xFF;
+        const uint8_t clearStencilValue =
+            static_cast<uint8_t>(params.depthStencilClearValue.stencil);
 
         pipelineDesc.setStencilTestEnabled(true);
         pipelineDesc.setStencilFrontFuncs(clearStencilValue, VK_COMPARE_OP_ALWAYS, compareMask);
@@ -1453,8 +1474,11 @@ angle::Result UtilsVk::clearFramebuffer(ContextVk *contextVk,
     VkViewport viewport;
     gl::Rectangle completeRenderArea = framebuffer->getRotatedCompleteRenderArea(contextVk);
     bool invertViewport              = contextVk->isViewportFlipEnabledForDrawFBO();
-    gl_vk::GetViewport(completeRenderArea, 0.0f, 1.0f, invertViewport, completeRenderArea.height,
-                       &viewport);
+    // Set depth range to clear value.  If clearing depth, the vertex shader depth output is clamped
+    // to this value, thus clearing the depth buffer to the desired clear value.
+    const float clearDepthValue = params.depthStencilClearValue.depth;
+    gl_vk::GetViewport(completeRenderArea, clearDepthValue, clearDepthValue, invertViewport,
+                       completeRenderArea.height, &viewport);
     pipelineDesc.setViewport(viewport);
 
     pipelineDesc.setScissor(gl_vk::GetRect(params.clearArea));
@@ -2576,13 +2600,14 @@ angle::Result UtilsVk::allocateDescriptorSet(ContextVk *contextVk,
 
 UtilsVk::ClearFramebufferParameters::ClearFramebufferParameters()
     : clearColor(false),
+      clearDepth(false),
       clearStencil(false),
       stencilMask(0),
       colorMaskFlags(0),
       colorAttachmentIndexGL(0),
       colorFormat(nullptr),
       colorClearValue{},
-      stencilClearValue(0)
+      depthStencilClearValue{}
 {}
 
 }  // namespace rx

src/libANGLE/renderer/vulkan/UtilsVk.h

@@ -20,7 +20,7 @@
 //      resolve on depth/stencil images.
 //    - Generate mipmap: Used by TextureVk::generateMipmapsWithCompute().
 //    - Overlay Cull/Draw: Used by OverlayVk to efficiently draw a UI for debugging.
-//    - Mipmap generation: Not yet implemented
+//    - Mipmap generation: Used by TextureVk to generate mipmaps more efficiently in compute.
 //
 
 #ifndef LIBANGLE_RENDERER_VULKAN_UTILSVK_H_
@@ -95,8 +95,10 @@ class UtilsVk : angle::NonCopyable
 
         gl::Rectangle clearArea;
 
-        // Note that depth clear is never needed to be done with a draw call.
+        // Note that depth clear is only possible if the depthClamp Vulkan feature is supported.  If
+        // needs be, this can be emulated by exporting depth from shaders/src/ImageClear.frag.
         bool clearColor;
+        bool clearDepth;
         bool clearStencil;
 
         uint8_t stencilMask;
@@ -105,7 +107,7 @@ class UtilsVk : angle::NonCopyable
         const angle::Format *colorFormat;
 
         VkClearColorValue colorClearValue;
-        uint8_t stencilClearValue;
+        VkClearDepthStencilValue depthStencilClearValue;
     };
 
     struct BlitResolveParameters

src/libANGLE/renderer/vulkan/vk_cache_utils.cpp

@@ -2178,6 +2178,11 @@ void GraphicsPipelineDesc::setDepthFunc(VkCompareOp op)
     SetBitField(mDepthStencilStateInfo.depthCompareOp, op);
 }
 
+void GraphicsPipelineDesc::setDepthClampEnabled(bool enabled)
+{
+    mRasterizationAndMultisampleStateInfo.bits.depthClampEnable = enabled;
+}
+
 void GraphicsPipelineDesc::setStencilTestEnabled(bool enabled)
 {
     mDepthStencilStateInfo.enable.stencilTest = enabled;

src/libANGLE/renderer/vulkan/vk_cache_utils.h

@@ -623,6 +623,7 @@ class GraphicsPipelineDesc final
     void setDepthTestEnabled(bool enabled);
     void setDepthWriteEnabled(bool enabled);
     void setDepthFunc(VkCompareOp op);
+    void setDepthClampEnabled(bool enabled);
     void setStencilTestEnabled(bool enabled);
     void setStencilFrontFuncs(uint8_t reference, VkCompareOp compareOp, uint8_t compareMask);
     void setStencilBackFuncs(uint8_t reference, VkCompareOp compareOp, uint8_t compareMask);