Add discard support to Vulkan

src/gpu/vk/GrVkGpuCommandBuffer.cpp

Index: src/gpu/vk/GrVkGpuCommandBuffer.cpp
diff --git a/src/gpu/vk/GrVkGpuCommandBuffer.cpp b/src/gpu/vk/GrVkGpuCommandBuffer.cpp
index dc553e03772329aa4f03e9d75970a4acfd34ef4c..52fb55bf064618124268fcc5d566dc1ce13a729b 100644
--- a/src/gpu/vk/GrVkGpuCommandBuffer.cpp
+++ b/src/gpu/vk/GrVkGpuCommandBuffer.cpp
@@ -130,6 +130,38 @@ void GrVkGpuCommandBuffer::onSubmit(const SkIRect& bounds) {
                                        fRenderTarget, bounds);
 }
 
+void GrVkGpuCommandBuffer::discard(GrRenderTarget* target) {
+    if (fIsEmpty) {
+        // We will change the render pass to do a clear load instead
+        GrVkRenderPass::LoadStoreOps vkColorOps(VK_ATTACHMENT_LOAD_OP_DONT_CARE,
+                                                VK_ATTACHMENT_STORE_OP_STORE);
+        GrVkRenderPass::LoadStoreOps vkStencilOps(VK_ATTACHMENT_LOAD_OP_LOAD,

[jvanverth1, 2016/06/29 16:00:30]

Shouldn't this and the resolve be LOAD_OP_DONT_CARE as well?

[egdaniel, 2016/06/29 16:11:30]

In general, when we call discard on a RT do we mean it for both color and
stencil?

In a follow on CL I'm actually going to experiment with making stencil DONT_CARE
always for both load and store (there are some unlucky situations where this
could cause a bug, but we'll see how bad it is/isn't).

For resolve it doesn't matter right now what we put here since it is not used.

[bsalomon, 2016/06/29 17:45:24]

both, I guess? The current discard stuff is not useful in the GL backend so
redefine it as you see fit.

+                                                  VK_ATTACHMENT_STORE_OP_STORE);
+        GrVkRenderPass::LoadStoreOps vkResolveOps(VK_ATTACHMENT_LOAD_OP_LOAD,
+                                                  VK_ATTACHMENT_STORE_OP_STORE);
+
+        const GrVkRenderPass* oldRP = fRenderPass;
+
+        GrVkRenderTarget* vkRT = static_cast<GrVkRenderTarget*>(target);
+        const GrVkResourceProvider::CompatibleRPHandle& rpHandle =
+            vkRT->compatibleRenderPassHandle();
+        if (rpHandle.isValid()) {
+            fRenderPass = fGpu->resourceProvider().findRenderPass(rpHandle,
+                                                                  vkColorOps,
+                                                                  vkResolveOps,
+                                                                  vkStencilOps);
+        } else {
+            fRenderPass = fGpu->resourceProvider().findRenderPass(*vkRT,
+                                                                  vkColorOps,
+                                                                  vkResolveOps,
+                                                                  vkStencilOps);
+        }
+
+        SkASSERT(fRenderPass->isCompatible(*oldRP));
+        oldRP->unref(fGpu);
+    }
+}
+
 void GrVkGpuCommandBuffer::onClearStencilClip(GrRenderTarget* target,
                                               const SkIRect& rect,
                                               bool insideClip) {