Improve usage of window rectangles

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 466af6c6ab4bda73273d0361dfe8fc82b376c704..e002d5101bab5a114a75f5ea8d0e219989d0a675 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -564,7 +564,7 @@ void GrGLGpu::onResetContext(uint32_t resetBits) {
 
     if (resetBits & kView_GrGLBackendState) {
         fHWScissorSettings.invalidate();
-        fHWWindowRects.invalidate();
+        fHWWindowRectsState.invalidate();
         fHWViewport.invalidate();
     }
 
@@ -1997,39 +1997,42 @@ void GrGLGpu::flushScissor(const GrScissorState& scissorState,
     this->disableScissor();
 }
 
-void GrGLGpu::flushWindowRectangles(const GrWindowRectangles& windows, const GrGLRenderTarget* rt) {
-    typedef GrWindowRectangles::Mode Mode;
-    SkASSERT(windows.count() <= this->caps()->maxWindowRectangles());
-    SkASSERT(windows.disabled() || rt->renderFBOID()); // Window rectangles can't be used on-screen.
+void GrGLGpu::flushWindowRectangles(const GrWindowRectsState& windowState,
+                                    const GrGLRenderTarget* rt) {
+    typedef GrWindowRectsState::Mode Mode;
+    SkASSERT(!windowState.enabled() || rt->renderFBOID()); // Window rects can't be used on-screen.
+    SkASSERT(windowState.numWindows() <= this->caps()->maxWindowRectangles());
 
     if (!this->caps()->maxWindowRectangles() ||
-        fHWWindowRects.equal(rt->origin(), rt->getViewport(), windows)) {
+        fHWWindowRectsState.knownEqualTo(rt->origin(), rt->getViewport(), windowState)) {
         return;
     }
 
     // This is purely a workaround for a spurious warning generated by gcc. Otherwise the above
     // assert would be sufficient. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=5912
-    int numWindows = SkTMin(windows.count(), int(GrWindowRectangles::kMaxWindows));
-    SkASSERT(windows.count() == numWindows);
+    int numWindows = SkTMin(windowState.numWindows(), int(GrWindowRectangles::kMaxWindows));
+    SkASSERT(windowState.numWindows() == numWindows);
 
     GrGLIRect glwindows[GrWindowRectangles::kMaxWindows];
-    const SkIRect* skwindows = windows.data();
+    const SkIRect* skwindows = windowState.windows().data();
+    int dx = -windowState.origin().x(), dy = -windowState.origin().y();
     for (int i = 0; i < numWindows; ++i) {
-        glwindows[i].setRelativeTo(rt->getViewport(), skwindows[i], rt->origin());
+        const SkIRect& skwindow = skwindows[i].makeOffset(dx, dy);
+        glwindows[i].setRelativeTo(rt->getViewport(), skwindow, rt->origin());
     }
 
-    GrGLenum glmode = (Mode::kExclusive == windows.mode()) ? GR_GL_EXCLUSIVE : GR_GL_INCLUSIVE;
+    GrGLenum glmode = (Mode::kExclusive == windowState.mode()) ? GR_GL_EXCLUSIVE : GR_GL_INCLUSIVE;
     GL_CALL(WindowRectangles(glmode, numWindows, glwindows->asInts()));
 
-    fHWWindowRects.set(rt->origin(), rt->getViewport(), windows);
+    fHWWindowRectsState.set(rt->origin(), rt->getViewport(), windowState);
 }
 
 void GrGLGpu::disableWindowRectangles() {
-    if (!this->caps()->maxWindowRectangles() || fHWWindowRects.disabled()) {
+    if (!this->caps()->maxWindowRectangles() || fHWWindowRectsState.knownDisabled()) {
         return;
     }
     GL_CALL(WindowRectangles(GR_GL_EXCLUSIVE, 0, nullptr));
-    fHWWindowRects.setDisabled();
+    fHWWindowRectsState.setDisabled();
 }
 
 void GrGLGpu::flushMinSampleShading(float minSampleShading) {
@@ -2079,7 +2082,7 @@ bool GrGLGpu::flushGLState(const GrPipeline& pipeline, const GrPrimitiveProcesso
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(pipeline.getRenderTarget());
     this->flushStencil(pipeline.getStencil());
     this->flushScissor(pipeline.getScissorState(), glRT->getViewport(), glRT->origin());
-    this->flushWindowRectangles(pipeline.getWindowRectangles(), glRT);
+    this->flushWindowRectangles(pipeline.getWindowRectsState(), glRT);
     this->flushHWAAState(glRT, pipeline.isHWAntialiasState(), !pipeline.getStencil().isDisabled());
 
     // This must come after textures are flushed because a texture may need
@@ -2207,7 +2210,7 @@ void GrGLGpu::clear(const GrFixedClip& clip, GrColor color, GrRenderTarget* targ
 
     this->flushRenderTarget(glRT, clip.scissorEnabled() ? &clip.scissorRect() : nullptr);
     this->flushScissor(clip.scissorState(), glRT->getViewport(), glRT->origin());
-    this->disableWindowRectangles();
+    this->flushWindowRectangles(clip.windowRectsState(), glRT);
 
     GrGLfloat r, g, b, a;
     static const GrGLfloat scale255 = 1.f / 255.f;
@@ -2271,7 +2274,7 @@ void GrGLGpu::clearStencilClip(const GrFixedClip& clip,
     this->flushRenderTarget(glRT, &SkIRect::EmptyIRect());
 
     this->flushScissor(clip.scissorState(), glRT->getViewport(), glRT->origin());
-    this->disableWindowRectangles();
+    this->flushWindowRectangles(clip.windowRectsState(), glRT);
 
     GL_CALL(StencilMask((uint32_t) clipStencilMask));
     GL_CALL(ClearStencil(value));