Reduce stencil buffer clearing

TBR=bsalomon@google.com
Bug: skia:6953
Change-Id: I079f90711297ee290f2d4011cfcb18b764554deb
Reviewed-on: https://skia-review.googlesource.com/40691
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>

gn/gpu.gni

@@ -403,6 +403,7 @@ skia_gpu_sources = [
   "$_src/gpu/gl/GrGLGLSL.h",
   "$_src/gpu/gl/GrGLGpu.cpp",
   "$_src/gpu/gl/GrGLGpu.h",
+  "$_src/gpu/gl/GrGLGpuCommandBuffer.cpp",
   "$_src/gpu/gl/GrGLGpuCommandBuffer.h",
   "$_src/gpu/gl/GrGLGpuProgramCache.cpp",
   "$_src/gpu/gl/GrGLExtensions.cpp",

include/gpu/GrRenderTarget.h

@@ -25,6 +25,8 @@ class GrStencilAttachment;
  */
 class GrRenderTarget : virtual public GrSurface {
 public:
+    virtual bool alwaysClearStencil() const { return false; }
+
     // GrSurface overrides
     GrRenderTarget* asRenderTarget() override { return this; }
     const GrRenderTarget* asRenderTarget() const  override { return this; }

src/gpu/GrRenderTargetOpList.cpp

@@ -97,7 +97,7 @@ static std::unique_ptr<GrGpuRTCommandBuffer> create_command_buffer(GrGpu* gpu,
                                                                    GrLoadOp colorLoadOp,
                                                                    GrColor loadClearColor,
                                                                    GrLoadOp stencilLoadOp) {
-    const GrGpuRTCommandBuffer::LoadAndStoreInfo kBasicLoadStoreInfo {
+    const GrGpuRTCommandBuffer::LoadAndStoreInfo kColorLoadStoreInfo {
         colorLoadOp,
         GrStoreOp::kStore,
         loadClearColor
@@ -115,8 +115,8 @@ static std::unique_ptr<GrGpuRTCommandBuffer> create_command_buffer(GrGpu* gpu,
 
     std::unique_ptr<GrGpuRTCommandBuffer> buffer(
                             gpu->createCommandBuffer(rt, origin,
-                                                     kBasicLoadStoreInfo,       // Color
-                                                     stencilLoadAndStoreInfo)); // Stencil
+                                                     kColorLoadStoreInfo,
+                                                     stencilLoadAndStoreInfo));
     return buffer;
 }
 

src/gpu/GrResourceProvider.cpp

@@ -451,6 +451,7 @@ GrStencilAttachment* GrResourceProvider::attachStencilAttachment(GrRenderTarget*
             height = SkNextPow2(height);
         }
 #endif
+        SkDEBUGCODE(bool newStencil = false;)
         GrStencilAttachment::ComputeSharedStencilAttachmentKey(width, height,
                                                                rt->numStencilSamples(), &sbKey);
         GrStencilAttachment* stencil = static_cast<GrStencilAttachment*>(
@@ -460,13 +461,18 @@ GrStencilAttachment* GrResourceProvider::attachStencilAttachment(GrRenderTarget*
             stencil = this->gpu()->createStencilAttachmentForRenderTarget(rt, width, height);
             if (stencil) {
                 this->assignUniqueKeyToResource(sbKey, stencil);
+                SkDEBUGCODE(newStencil = true;)
             }
         }
         if (rt->renderTargetPriv().attachStencilAttachment(stencil)) {
 #ifdef SK_DEBUG
             // Fill the SB with an inappropriate value. opLists that use the
             // SB should clear it properly.
-            this->gpu()->clearStencil(rt, 0xFFFF);
+            if (newStencil) {
+                SkASSERT(stencil->isDirty());
+                this->gpu()->clearStencil(rt, 0xFFFF);
+                SkASSERT(stencil->isDirty());
+            }
 #endif
         }
     }

src/gpu/GrStencilAttachment.h

@@ -17,9 +17,7 @@ class GrResourceKey;
 
 class GrStencilAttachment : public GrGpuResource {
 public:
-
-
-    virtual ~GrStencilAttachment() {
+    ~GrStencilAttachment() override {
         // TODO: allow SB to be purged and detach itself from rts
     }
 
@@ -27,6 +25,9 @@ public:
     int height() const { return fHeight; }
     int bits() const { return fBits; }
     int numSamples() const { return fSampleCnt; }
+    bool isDirty() const { return fIsDirty; }
+
+    void cleared() { fIsDirty = false; }
 
     // We create a unique stencil buffer at each width, height and sampleCnt and share it for
     // all render targets that require a stencil with those params.
@@ -35,11 +36,12 @@ public:
 
 protected:
     GrStencilAttachment(GrGpu* gpu, int width, int height, int bits, int sampleCnt)
-        : GrGpuResource(gpu)
-        , fWidth(width)
-        , fHeight(height)
-        , fBits(bits)
-        , fSampleCnt(sampleCnt) {
+            : INHERITED(gpu)
+            , fWidth(width)
+            , fHeight(height)
+            , fBits(bits)
+            , fSampleCnt(sampleCnt)
+            , fIsDirty(true) {
     }
 
 private:
@@ -48,6 +50,7 @@ private:
     int fHeight;
     int fBits;
     int fSampleCnt;
+    bool fIsDirty;
 
     typedef GrGpuResource INHERITED;
 };

src/gpu/gl/GrGLGpu.cpp

@@ -1960,6 +1960,12 @@ void GrGLGpu::clearStencil(GrRenderTarget* target, int clearValue) {
     if (!target) {
         return;
     }
+
+    GrStencilAttachment* sb = target->renderTargetPriv().getStencilAttachment();
+    // this should only be called internally when we know we have a
+    // stencil buffer.
+    SkASSERT(sb);
+
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(target);
     this->flushRenderTarget(glRT, &SkIRect::EmptyIRect());
 
@@ -1970,6 +1976,9 @@ void GrGLGpu::clearStencil(GrRenderTarget* target, int clearValue) {
     GL_CALL(ClearStencil(clearValue));
     GL_CALL(Clear(GR_GL_STENCIL_BUFFER_BIT));
     fHWStencilSettings.invalidate();
+    if (!clearValue) {
+        sb->cleared();
+    }
 }
 
 void GrGLGpu::clearStencilClip(const GrFixedClip& clip,

src/gpu/gl/GrGLGpuCommandBuffer.cpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrGLGpuCommandBuffer.h"
+
+#include "GrFixedClip.h"
+#include "GrRenderTargetPriv.h"
+
+void GrGLGpuRTCommandBuffer::begin() {
+    if (GrLoadOp::kClear == fColorLoadAndStoreInfo.fLoadOp) {
+        fGpu->clear(GrFixedClip::Disabled(), fColorLoadAndStoreInfo.fClearColor,
+                    fRenderTarget, fOrigin);
+    }
+    if (GrLoadOp::kClear == fStencilLoadAndStoreInfo.fLoadOp) {
+        GrStencilAttachment* sb = fRenderTarget->renderTargetPriv().getStencilAttachment();
+        if (sb && (sb->isDirty() || fRenderTarget->alwaysClearStencil())) {
+            fGpu->clearStencil(fRenderTarget, 0x0);
+        }
+    }
+}

src/gpu/gl/GrGLGpuCommandBuffer.h

@@ -61,15 +61,7 @@ public:
 
     ~GrGLGpuRTCommandBuffer() override {}
 
-    void begin() override {
-        if (GrLoadOp::kClear == fColorLoadAndStoreInfo.fLoadOp) {
-            fGpu->clear(GrFixedClip::Disabled(), fColorLoadAndStoreInfo.fClearColor,
-                        fRenderTarget, fOrigin);
-        }
-        if (GrLoadOp::kClear == fStencilLoadAndStoreInfo.fLoadOp) {
-            fGpu->clearStencil(fRenderTarget, 0x0);
-        }
-    }
+    void begin() override;
     void end() override {}
 
     void discard() override { }

src/gpu/gl/GrGLRenderTarget.cpp

@@ -75,7 +75,7 @@ sk_sp<GrGLRenderTarget> GrGLRenderTarget::MakeWrapped(GrGLGpu* gpu,
         format.fPacked = false;
         format.fStencilBits = stencilBits;
         format.fTotalBits = stencilBits;
-        // Owndership of sb is passed to the GrRenderTarget so doesn't need to be deleted
+        // Ownership of sb is passed to the GrRenderTarget so doesn't need to be deleted
         sb = new GrGLStencilAttachment(gpu, sbDesc, desc.fWidth, desc.fHeight,
                                        desc.fSampleCnt, format);
     }

src/gpu/gl/GrGLRenderTarget.h

@@ -19,6 +19,8 @@ class GrGLStencilAttachment;
 
 class GrGLRenderTarget : public GrRenderTarget {
 public:
+    bool alwaysClearStencil() const override { return 0 == fRTFBOID; }
+
     // set fTexFBOID to this value to indicate that it is multisampled but
     // Gr doesn't know how to resolve it.
     enum { kUnresolvableFBOID = 0 };