Improve usage of window rectangles

gm/windowrectangles.cpp

Index: gm/windowrectangles.cpp
diff --git a/gm/windowrectangles.cpp b/gm/windowrectangles.cpp
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+++ b/gm/windowrectangles.cpp
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+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkClipStack.h"
+#include "SkRRect.h"
+
+#if SK_SUPPORT_GPU
+#  include "GrAppliedClip.h"
+#  include "GrDrawContext.h"
+#  include "GrDrawContextPriv.h"
+#  include "GrFixedClip.h"
+#  include "GrReducedClip.h"
+#  include "GrRenderTargetPriv.h"
+#  include "GrResourceProvider.h"
+#  include "effects/GrTextureDomain.h"
+#endif
+
+constexpr static SkIRect kDeviceRect = {0, 0, 600, 600};
+constexpr static SkIRect kLayerRect = {25, 25, 575, 575};
+constexpr static SkIRect kCoverRect = {50, 50, 550, 550};
+constexpr static int kNumWindows = 8;
+
+namespace skiagm {
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class WindowRectanglesBaseGM : public GM {
+protected:
+    virtual void onCoverClipStack(const SkClipStack&, SkCanvas*) = 0;
+
+private:
+    SkISize onISize() override { return SkISize::Make(kDeviceRect.width(), kDeviceRect.height()); }
+    void onDraw(SkCanvas*) final;
+};
+
+void WindowRectanglesBaseGM::onDraw(SkCanvas* canvas) {
+    sk_tool_utils::draw_checkerboard(canvas, 0xffffffff, 0xffc6c3c6, 25);
+    canvas->saveLayer(SkRect::Make(kLayerRect), nullptr);
+
+    SkClipStack stack;
+    stack.clipDevRect(SkRect::MakeXYWH(370.75, 80.25, 149, 100), SkRegion::kDifference_Op, false);
+    stack.clipDevRect(SkRect::MakeXYWH(80.25, 420.75, 150, 100), SkRegion::kDifference_Op, true);
+    stack.clipDevRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(200, 200, 200, 200), 60, 45),
+                       SkRegion::kDifference_Op, true);
+
+    SkRRect nine;
+    nine.setNinePatch(SkRect::MakeXYWH(550 - 30.25 - 100, 370.75, 100, 150), 12, 35, 23, 20);
+    stack.clipDevRRect(nine, SkRegion::kDifference_Op, true);
+
+    SkRRect complx;
+    SkVector complxRadii[4] = {{6, 4}, {8, 12}, {16, 24}, {48, 32}};
+    complx.setRectRadii(SkRect::MakeXYWH(80.25, 80.75, 100, 149), complxRadii);
+    stack.clipDevRRect(complx, SkRegion::kDifference_Op, false);
+
+    this->onCoverClipStack(stack, canvas);
+
+    canvas->restore();
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Draws a clip that will exercise window rectangles if they are supported.
+ */
+class WindowRectanglesGM : public WindowRectanglesBaseGM {
+private:
+    SkString onShortName() final { return SkString("windowrectangles"); }
+    void onCoverClipStack(const SkClipStack&, SkCanvas*) final;
+};
+
+/**
+ * This is a simple helper class for resetting a canvas's clip to our test’s SkClipStack.
+ */
+class ReplayClipStackVisitor final : public SkCanvasClipVisitor {
+public:
+    typedef SkRegion::Op Op;
+    ReplayClipStackVisitor(SkCanvas* canvas) : fCanvas(canvas) {}
+    void clipRect(const SkRect& r, Op op, bool aa) override { fCanvas->clipRect(r, op, aa); }
+    void clipRRect(const SkRRect& rr, Op op, bool aa) override { fCanvas->clipRRect(rr, op, aa); }
+    void clipPath(const SkPath&, Op, bool) override { SkFAIL("Not implemented"); }
+private:
+    SkCanvas* const fCanvas;
+};
+
+void WindowRectanglesGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setColor(0xff00aa80);
+
+    // Set up the canvas's clip to match our SkClipStack.
+    ReplayClipStackVisitor visitor(canvas);
+    SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
+    for (const SkClipStack::Element* element = iter.next(); element; element = iter.next()) {
+        element->replay(&visitor);
+    }
+
+    canvas->drawRect(SkRect::Make(kCoverRect), paint);
+}
+
+DEF_GM( return new WindowRectanglesGM(); )
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#if SK_SUPPORT_GPU
+
+/**
+ * Visualizes the mask (alpha or stencil) for a clip with several window rectangles. The purpose of
+ * this test is to verify that window rectangles are being used during clip mask generation, and to
+ * visualize where the window rectangles are placed.
+ *
+ * We use window rectangles when generating the clip mask because there is no need to invest time
+ * defining those regions where window rectangles will be in effect during the actual draw anyway.
+ *
+ * This test works by filling the entire clip mask with a small checkerboard pattern before drawing
+ * it, and then covering the mask with a solid color once it has been generated. The regions inside
+ * window rectangles or outside the scissor should still have the initial checkerboard intact.
+ */
+class WindowRectanglesMaskGM : public WindowRectanglesBaseGM {
+private:
+    constexpr static int kMaskCheckerSize = 5;
+    SkString onShortName() final { return SkString("windowrectangles_mask"); }
+    void onCoverClipStack(const SkClipStack&, SkCanvas*) final;
+    void visualizeAlphaMask(GrContext*, GrDrawContext*, const GrReducedClip&, const GrPaint&);
+    void visualizeStencilMask(GrContext*, GrDrawContext*, const GrReducedClip&, const GrPaint&);
+    void stencilCheckerboard(GrDrawContext*, bool flip);
+    void fail(SkCanvas*);
+};
+
+/**
+ * Base class for GrClips that visualize a clip mask.
+ */
+class MaskOnlyClipBase : public GrClip {
+private:
+    bool quickContains(const SkRect&) const final { return false; }
+    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const final { return false; }
+    void getConservativeBounds(int width, int height, SkIRect* rect, bool* iior) const final {
+        rect->set(0, 0, width, height);
+        if (iior) {
+            *iior = false;
+        }
+    }
+};
+
+/**
+ * This class clips a cover by an alpha mask. We use it to visualize the alpha clip mask.
+ */
+class AlphaOnlyClip final : public MaskOnlyClipBase {
+public:
+    AlphaOnlyClip(GrTexture* mask, int x, int y) {
+        int w = mask->width(), h = mask->height();
+        SkMatrix mat = SkMatrix::MakeScale(1.f / SkIntToScalar(w), 1.f / SkIntToScalar(h));
+        mat.preTranslate(SkIntToScalar(-x), SkIntToScalar(-y));
+        fFP = GrTextureDomainEffect::Make(
+                  mask, nullptr, mat,
+                  GrTextureDomain::MakeTexelDomain(mask, SkIRect::MakeWH(w, h)),
+                  GrTextureDomain::kDecal_Mode, GrTextureParams::kNone_FilterMode,
+                  kDevice_GrCoordSet);
+
+    }
+private:
+    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip* out) const override {
+        out->addCoverageFP(fFP);
+        return true;
+    }
+    sk_sp<GrFragmentProcessor> fFP;
+};
+
+/**
+ * This class clips a cover by the stencil clip bit. We use it to visualize the stencil mask.
+ */
+class StencilOnlyClip final : public MaskOnlyClipBase {
+private:
+    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip* out) const override {
+        out->addStencilClip();
+        return true;
+    }
+};
+
+void WindowRectanglesMaskGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
+    GrContext* ctx = canvas->getGrContext();
+    GrDrawContext* dc = canvas->internal_private_accessTopLayerDrawContext();
+
+    if (!ctx || !dc ||
+        dc->accessRenderTarget()->renderTargetPriv().maxWindowRectangles() < kNumWindows) {
+        this->fail(canvas);
+        return;
+    }
+
+    const GrReducedClip reducedClip(stack, SkRect::Make(kCoverRect), kNumWindows);
+
+    GrPaint paint;
+    paint.setAntiAlias(true);
+    if (!dc->isStencilBufferMultisampled()) {
+        paint.setColor4f(GrColor4f(0, 0.25f, 1, 1));
+        this->visualizeAlphaMask(ctx, dc, reducedClip, paint);
+    } else {
+        paint.setColor4f(GrColor4f(1, 0.25f, 0.25f, 1));
+        this->visualizeStencilMask(ctx, dc, reducedClip, paint);
+    }
+}
+
+void WindowRectanglesMaskGM::visualizeAlphaMask(GrContext* ctx, GrDrawContext* dc,
+                                                const GrReducedClip& reducedClip,
+                                                const GrPaint& paint) {
+    sk_sp<GrDrawContext> maskDC(
+        ctx->makeDrawContextWithFallback(SkBackingFit::kExact, kLayerRect.width(),
+                                         kLayerRect.height(), kAlpha_8_GrPixelConfig, nullptr));
+    if (!maskDC ||
+        !ctx->resourceProvider()->attachStencilAttachment(maskDC->accessRenderTarget())) {
+        return;
+    }
+
+    // Draw a checker pattern into the alpha mask so we can visualize the regions left untouched by
+    // the clip mask generation.
+    this->stencilCheckerboard(maskDC.get(), true);
+    maskDC->clear(nullptr, GrColorPackA4(0xff), true);
+    maskDC->drawContextPriv().drawAndStencilRect(StencilOnlyClip(), &GrUserStencilSettings::kUnused,
+                                                 SkRegion::kDifference_Op, false, false,
+                                                 SkMatrix::I(),
+                                                 SkRect::MakeIWH(maskDC->width(), maskDC->height()));
+    reducedClip.drawAlphaClipMask(maskDC.get());
+    sk_sp<GrTexture> mask(maskDC->asTexture());
+
+    int x = kCoverRect.x() - kLayerRect.x(),
+        y = kCoverRect.y() - kLayerRect.y();
+
+    // Now visualize the alpha mask by drawing a rect over the area where it is defined. The regions
+    // inside window rectangles or outside the scissor should still have the initial checkerboard
+    // intact. (This verifies we didn't spend any time modifying those pixels in the mask.)
+    AlphaOnlyClip clip(mask.get(), x, y);
+    dc->drawRect(clip, paint, SkMatrix::I(),
+                 SkRect::Make(SkIRect::MakeXYWH(x, y, mask->width(), mask->height())));
+}
+
+void WindowRectanglesMaskGM::visualizeStencilMask(GrContext* ctx, GrDrawContext* dc,
+                                                  const GrReducedClip& reducedClip,
+                                                  const GrPaint& paint) {
+    if (!ctx->resourceProvider()->attachStencilAttachment(dc->accessRenderTarget())) {
+        return;
+    }
+
+    // Draw a checker pattern into the stencil buffer so we can visualize the regions left untouched
+    // by the clip mask generation.
+    this->stencilCheckerboard(dc, false);
+    reducedClip.drawStencilClipMask(ctx, dc, {kLayerRect.x(), kLayerRect.y()});
+
+    // Now visualize the stencil mask by covering the entire render target. The regions inside
+    // window rectangless or outside the scissor should still have the initial checkerboard intact.
+    // (This verifies we didn't spend any time modifying those pixels in the mask.)
+    dc->drawPaint(StencilOnlyClip(), paint, SkMatrix::I());
+}
+
+void WindowRectanglesMaskGM::stencilCheckerboard(GrDrawContext* dc, bool flip) {
+    constexpr static GrUserStencilSettings kSetClip(
+        GrUserStencilSettings::StaticInit<
+        0,
+        GrUserStencilTest::kAlways,
+        0,
+        GrUserStencilOp::kSetClipBit,
+        GrUserStencilOp::kKeep,
+        0>()
+    );
+
+    dc->drawContextPriv().clearStencilClip(GrFixedClip::Disabled(), false);
+
+    for (int y = 0; y < kLayerRect.height(); y += kMaskCheckerSize) {
+        for (int x = (y & 1) == flip ? 0 : kMaskCheckerSize;
+             x < kLayerRect.width(); x += 2 * kMaskCheckerSize) {
+            SkIRect checker = SkIRect::MakeXYWH(x, y, kMaskCheckerSize, kMaskCheckerSize);
+            dc->drawContextPriv().stencilRect(GrNoClip(), &kSetClip, false, SkMatrix::I(),
+                                              SkRect::Make(checker));
+        }
+    }
+}
+
+void WindowRectanglesMaskGM::fail(SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setTextAlign(SkPaint::kCenter_Align);
+    paint.setTextSize(20);
+    sk_tool_utils::set_portable_typeface(&paint);
+
+    SkString errorMsg;
+    errorMsg.printf("Requires GPU with %i window rectangles", kNumWindows);
+
+    canvas->clipRect(SkRect::Make(kCoverRect));
+    canvas->clear(SK_ColorWHITE);
+    canvas->drawText(errorMsg.c_str(), errorMsg.size(), SkIntToScalar(kCoverRect.centerX()),
+                     SkIntToScalar(kCoverRect.centerY() - 10), paint);
+}
+
+DEF_GM( return new WindowRectanglesMaskGM(); )
+
+#endif
+
+}