Add a full clear method to GrDrawTarget.

This will allow us to avoid ClearBatch creation for successive clears.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2233043002

Review-Url: https://codereview.chromium.org/2233043002

src/gpu/GrDrawContext.cpp

@@ -203,10 +203,12 @@ void GrDrawContext::clear(const SkIRect* rect,
 
     const SkIRect rtRect = SkIRect::MakeWH(this->width(), this->height());
     SkIRect clippedRect;
+    bool isFull = false;
     if (!rect ||
         (canIgnoreRect && fContext->caps()->fullClearIsFree()) ||
         rect->contains(rtRect)) {
         rect = &rtRect;
+        isFull = true;
     } else {
         clippedRect = *rect;
         if (!clippedRect.intersect(rtRect)) {
@@ -228,6 +230,8 @@ void GrDrawContext::clear(const SkIRect* rect,
         paint.setXPFactory(GrPorterDuffXPFactory::Make(SkXfermode::kSrc_Mode));
 
         this->drawRect(GrNoClip(), paint, SkMatrix::I(), SkRect::Make(*rect));
+    } else if (isFull) {
+        this->getDrawTarget()->fullClear(this->accessRenderTarget(), color);
     } else {
         sk_sp<GrBatch> batch = GrClearBatch::Make(*rect, color, this->accessRenderTarget());
         this->getDrawTarget()->addBatch(std::move(batch));

src/gpu/GrDrawTarget.cpp

@@ -26,6 +26,7 @@
 
 #include "SkStrokeRec.h"
 
+#include "batches/GrClearBatch.h"
 #include "batches/GrClearStencilClipBatch.h"
 #include "batches/GrCopySurfaceBatch.h"
 #include "batches/GrDiscardBatch.h"
@@ -456,7 +457,18 @@ void GrDrawTarget::addBatch(sk_sp<GrBatch> batch) {
     this->recordBatch(batch.get(), batch->bounds());
 }
 
+void GrDrawTarget::fullClear(GrRenderTarget* renderTarget, GrColor color) {
+    // Currently this just inserts a clear batch. However, once in MDB this can remove all the
+    // previously recorded batches and change the load op to clear with supplied color.
+    sk_sp<GrBatch> batch = GrClearBatch::Make(SkIRect::MakeWH(renderTarget->width(),
+                                                              renderTarget->height()),
+                                              color, renderTarget);
+    this->recordBatch(batch.get(), batch->bounds());
+}
+
 void GrDrawTarget::discard(GrRenderTarget* renderTarget) {
+    // Currently this just inserts a discard batch. However, once in MDB this can remove all the
+    // previously recorded batches and change the load op to discard.
     if (this->caps()->discardRenderTargetSupport()) {
         GrBatch* batch = new GrDiscardBatch(renderTarget);
         this->recordBatch(batch, batch->bounds());

src/gpu/GrDrawTarget.h

@@ -121,6 +121,9 @@ public:
                      const SkMatrix& viewMatrix,
                      const GrPath*);
 
+    /** Clears the entire render target */
+    void fullClear(GrRenderTarget*, GrColor color);
+
     /** Discards the contents render target. */
     void discard(GrRenderTarget*);