gm/windowrectangles.cpp - platform/external/skqp - Gitiles

 /*
  * 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 "sk_tool_utils.h"
 #include "SkClipStack.h"
 #include "SkRRect.h"

 #if SK_SUPPORT_GPU
 #  include "GrAppliedClip.h"
 #  include "GrStencilClip.h"
 #  include "GrReducedClip.h"
 #  include "GrRenderTargetContext.h"
 #  include "GrRenderTargetContextPriv.h"
 #  include "GrResourceProvider.h"
 #  include "effects/GrTextureDomain.h"
 #endif

 constexpr static SkIRect kDeviceRect = {0, 0, 600, 600};
 constexpr static SkIRect kCoverRect = {50, 50, 550, 550};

 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);

     SkClipStack stack;
     stack.clipRect(SkRect::MakeXYWH(370.75, 80.25, 149, 100), SkMatrix::I(),
                    kDifference_SkClipOp, false);
     stack.clipRect(SkRect::MakeXYWH(80.25, 420.75, 150, 100), SkMatrix::I(),
                    kDifference_SkClipOp, true);
     stack.clipRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(200, 200, 200, 200), 60, 45),
                     SkMatrix::I(), kDifference_SkClipOp, true);

     SkRRect nine;
     nine.setNinePatch(SkRect::MakeXYWH(550 - 30.25 - 100, 370.75, 100, 150), 12, 35, 23, 20);
     stack.clipRRect(nine, SkMatrix::I(), kDifference_SkClipOp, 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.clipRRect(complx, SkMatrix::I(), kDifference_SkClipOp, false);

     this->onCoverClipStack(stack, canvas);
 }

 ////////////////////////////////////////////////////////////////////////////////////////////////////

 /**
  * 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;
 };

 void WindowRectanglesGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
     SkPaint paint;
     paint.setColor(0xff00aa80);

     // Set up the canvas's clip to match our SkClipStack.
     SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
     for (const SkClipStack::Element* element = iter.next(); element; element = iter.next()) {
         SkClipOp op = element->getOp();
         bool isAA = element->isAA();
         switch (element->getDeviceSpaceType()) {
             case SkClipStack::Element::DeviceSpaceType::kPath:
                 canvas->clipPath(element->getDeviceSpacePath(), op, isAA);
                 break;
             case SkClipStack::Element::DeviceSpaceType::kRRect:
                 canvas->clipRRect(element->getDeviceSpaceRRect(), op, isAA);
                 break;
             case SkClipStack::Element::DeviceSpaceType::kRect:
                 canvas->clipRect(element->getDeviceSpaceRect(), op, isAA);
                 break;
             case SkClipStack::Element::DeviceSpaceType::kEmpty:
                 canvas->clipRect({ 0, 0, 0, 0 }, kIntersect_SkClipOp, false);
                 break;
         }
     }

     canvas->drawRect(SkRect::Make(kCoverRect), paint);
 }

 DEF_GM( return new WindowRectanglesGM(); )

 ////////////////////////////////////////////////////////////////////////////////////////////////////

 #if SK_SUPPORT_GPU

 constexpr static int kNumWindows = 8;

 /**
  * 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*, GrRenderTargetContext*, const GrReducedClip&, GrPaint&&);
     void visualizeStencilMask(GrContext*, GrRenderTargetContext*, const GrReducedClip&, GrPaint&&);
     void stencilCheckerboard(GrRenderTargetContext*, 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, GrAA*) 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(sk_sp<GrTextureProxy> mask, int x, int y) : fMask(mask), fX(x), fY(y) {}

 private:
     bool apply(GrContext*, GrRenderTargetContext*, bool, bool, GrAppliedClip* out,
                SkRect* bounds) const override {
         int w = fMask->width();
         int h = fMask->height();
         out->addCoverageFP(GrDeviceSpaceTextureDecalFragmentProcessor::Make(
                 fMask, SkIRect::MakeWH(w, h), {fX, fY}));
         return true;
     }
     sk_sp<GrTextureProxy> fMask;
     int fX;
     int fY;
 };

 /**
  * Makes a clip object that enforces the stencil clip bit. Used to visualize the stencil mask.
  */
 static GrStencilClip make_stencil_only_clip() {
     return GrStencilClip(SkClipStack::kEmptyGenID);
 };

 void WindowRectanglesMaskGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
     GrContext* ctx = canvas->getGrContext();
     GrRenderTargetContext* rtc = canvas->internal_private_accessTopLayerRenderTargetContext();

     if (!ctx || !rtc || rtc->priv().maxWindowRectangles() < kNumWindows) {
         this->fail(canvas);
         return;
     }

     const GrReducedClip reducedClip(stack, SkRect::Make(kCoverRect), rtc->caps()->shaderCaps(),
                                     kNumWindows);

     GrPaint paint;
     if (GrFSAAType::kNone == rtc->fsaaType()) {
         paint.setColor4f(GrColor4f(0, 0.25f, 1, 1));
         this->visualizeAlphaMask(ctx, rtc, reducedClip, std::move(paint));
     } else {
         paint.setColor4f(GrColor4f(1, 0.25f, 0.25f, 1));
         this->visualizeStencilMask(ctx, rtc, reducedClip, std::move(paint));
     }
 }

 void WindowRectanglesMaskGM::visualizeAlphaMask(GrContext* ctx, GrRenderTargetContext* rtc,
                                                 const GrReducedClip& reducedClip, GrPaint&& paint) {
     const int padRight = (kDeviceRect.right() - kCoverRect.right()) / 2;
     const int padBottom = (kDeviceRect.bottom() - kCoverRect.bottom()) / 2;
     sk_sp<GrRenderTargetContext> maskRTC(
         ctx->contextPriv().makeDeferredRenderTargetContextWithFallback(
                                                          SkBackingFit::kExact,
                                                          kCoverRect.width() + padRight,
                                                          kCoverRect.height() + padBottom,
                                                          kAlpha_8_GrPixelConfig, nullptr));
     if (!maskRTC) {
         return;
     }

     // Draw a checker pattern into the alpha mask so we can visualize the regions left untouched by
     // the clip mask generation.
     this->stencilCheckerboard(maskRTC.get(), true);
     maskRTC->clear(nullptr, GrColorPackA4(0xff), GrRenderTargetContext::CanClearFullscreen::kYes);
     maskRTC->priv().drawAndStencilRect(make_stencil_only_clip(), &GrUserStencilSettings::kUnused,
                                        SkRegion::kDifference_Op, false, GrAA::kNo, SkMatrix::I(),
                                        SkRect::MakeIWH(maskRTC->width(), maskRTC->height()));
     reducedClip.drawAlphaClipMask(maskRTC.get());

     int x = kCoverRect.x() - kDeviceRect.x(),
         y = kCoverRect.y() - kDeviceRect.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(maskRTC->asTextureProxyRef(), x, y);
     rtc->drawRect(clip, std::move(paint), GrAA::kYes, SkMatrix::I(),
                   SkRect::Make(SkIRect::MakeXYWH(x, y, maskRTC->width(), maskRTC->height())));
 }

 void WindowRectanglesMaskGM::visualizeStencilMask(GrContext* ctx, GrRenderTargetContext* rtc,
                                                   const GrReducedClip& reducedClip,
                                                   GrPaint&& paint) {
     // Draw a checker pattern into the stencil buffer so we can visualize the regions left untouched
     // by the clip mask generation.
     this->stencilCheckerboard(rtc, false);
     reducedClip.drawStencilClipMask(ctx, rtc);

     // Now visualize the stencil mask by covering the entire render target. 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.)
     rtc->drawPaint(make_stencil_only_clip(), std::move(paint), SkMatrix::I());
 }

 void WindowRectanglesMaskGM::stencilCheckerboard(GrRenderTargetContext* rtc, bool flip) {
     constexpr static GrUserStencilSettings kSetClip(
         GrUserStencilSettings::StaticInit<
         0,
         GrUserStencilTest::kAlways,
         0,
         GrUserStencilOp::kSetClipBit,
         GrUserStencilOp::kKeep,
         0>()
     );

     rtc->priv().clearStencilClip(GrFixedClip::Disabled(), false);

     for (int y = 0; y < kDeviceRect.height(); y += kMaskCheckerSize) {
         for (int x = (y & 1) == flip ? 0 : kMaskCheckerSize;
              x < kDeviceRect.width(); x += 2 * kMaskCheckerSize) {
             SkIRect checker = SkIRect::MakeXYWH(x, y, kMaskCheckerSize, kMaskCheckerSize);
             rtc->priv().stencilRect(GrNoClip(), &kSetClip, GrAAType::kNone, 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->drawString(errorMsg, SkIntToScalar(kCoverRect.centerX()),
                      SkIntToScalar(kCoverRect.centerY() - 10), paint);
 }

 DEF_GM( return new WindowRectanglesMaskGM(); )

 #endif

 }
	/*
	* 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 "sk_tool_utils.h"
	#include "SkClipStack.h"
	#include "SkRRect.h"

	#if SK_SUPPORT_GPU
	# include "GrAppliedClip.h"
	# include "GrStencilClip.h"
	# include "GrReducedClip.h"
	# include "GrRenderTargetContext.h"
	# include "GrRenderTargetContextPriv.h"
	# include "GrResourceProvider.h"
	# include "effects/GrTextureDomain.h"
	#endif

	constexpr static SkIRect kDeviceRect = {0, 0, 600, 600};
	constexpr static SkIRect kCoverRect = {50, 50, 550, 550};

	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);

	SkClipStack stack;
	stack.clipRect(SkRect::MakeXYWH(370.75, 80.25, 149, 100), SkMatrix::I(),
	kDifference_SkClipOp, false);
	stack.clipRect(SkRect::MakeXYWH(80.25, 420.75, 150, 100), SkMatrix::I(),
	kDifference_SkClipOp, true);
	stack.clipRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(200, 200, 200, 200), 60, 45),
	SkMatrix::I(), kDifference_SkClipOp, true);

	SkRRect nine;
	nine.setNinePatch(SkRect::MakeXYWH(550 - 30.25 - 100, 370.75, 100, 150), 12, 35, 23, 20);
	stack.clipRRect(nine, SkMatrix::I(), kDifference_SkClipOp, 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.clipRRect(complx, SkMatrix::I(), kDifference_SkClipOp, false);

	this->onCoverClipStack(stack, canvas);
	}

	////////////////////////////////////////////////////////////////////////////////////////////////////

	/**
	* 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;
	};

	void WindowRectanglesGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
	SkPaint paint;
	paint.setColor(0xff00aa80);

	// Set up the canvas's clip to match our SkClipStack.
	SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
	for (const SkClipStack::Element* element = iter.next(); element; element = iter.next()) {
	SkClipOp op = element->getOp();
	bool isAA = element->isAA();
	switch (element->getDeviceSpaceType()) {
	case SkClipStack::Element::DeviceSpaceType::kPath:
	canvas->clipPath(element->getDeviceSpacePath(), op, isAA);
	break;
	case SkClipStack::Element::DeviceSpaceType::kRRect:
	canvas->clipRRect(element->getDeviceSpaceRRect(), op, isAA);
	break;
	case SkClipStack::Element::DeviceSpaceType::kRect:
	canvas->clipRect(element->getDeviceSpaceRect(), op, isAA);
	break;
	case SkClipStack::Element::DeviceSpaceType::kEmpty:
	canvas->clipRect({ 0, 0, 0, 0 }, kIntersect_SkClipOp, false);
	break;
	}
	}

	canvas->drawRect(SkRect::Make(kCoverRect), paint);
	}

	DEF_GM( return new WindowRectanglesGM(); )

	////////////////////////////////////////////////////////////////////////////////////////////////////

	#if SK_SUPPORT_GPU

	constexpr static int kNumWindows = 8;

	/**
	* 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, GrRenderTargetContext, const GrReducedClip&, GrPaint&&);
	void visualizeStencilMask(GrContext, GrRenderTargetContext, const GrReducedClip&, GrPaint&&);
	void stencilCheckerboard(GrRenderTargetContext*, 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, GrAA*) 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(sk_sp<GrTextureProxy> mask, int x, int y) : fMask(mask), fX(x), fY(y) {}

	private:
	bool apply(GrContext, GrRenderTargetContext, bool, bool, GrAppliedClip* out,
	SkRect* bounds) const override {
	int w = fMask->width();
	int h = fMask->height();
	out->addCoverageFP(GrDeviceSpaceTextureDecalFragmentProcessor::Make(
	fMask, SkIRect::MakeWH(w, h), {fX, fY}));
	return true;
	}
	sk_sp<GrTextureProxy> fMask;
	int fX;
	int fY;
	};

	/**
	* Makes a clip object that enforces the stencil clip bit. Used to visualize the stencil mask.
	*/
	static GrStencilClip make_stencil_only_clip() {
	return GrStencilClip(SkClipStack::kEmptyGenID);
	};

	void WindowRectanglesMaskGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
	GrContext* ctx = canvas->getGrContext();
	GrRenderTargetContext* rtc = canvas->internal_private_accessTopLayerRenderTargetContext();

	if (!ctx \|\| !rtc \|\| rtc->priv().maxWindowRectangles() < kNumWindows) {
	this->fail(canvas);
	return;
	}

	const GrReducedClip reducedClip(stack, SkRect::Make(kCoverRect), rtc->caps()->shaderCaps(),
	kNumWindows);

	GrPaint paint;
	if (GrFSAAType::kNone == rtc->fsaaType()) {
	paint.setColor4f(GrColor4f(0, 0.25f, 1, 1));
	this->visualizeAlphaMask(ctx, rtc, reducedClip, std::move(paint));
	} else {
	paint.setColor4f(GrColor4f(1, 0.25f, 0.25f, 1));
	this->visualizeStencilMask(ctx, rtc, reducedClip, std::move(paint));
	}
	}

	void WindowRectanglesMaskGM::visualizeAlphaMask(GrContext* ctx, GrRenderTargetContext* rtc,
	const GrReducedClip& reducedClip, GrPaint&& paint) {
	const int padRight = (kDeviceRect.right() - kCoverRect.right()) / 2;
	const int padBottom = (kDeviceRect.bottom() - kCoverRect.bottom()) / 2;
	sk_sp<GrRenderTargetContext> maskRTC(
	ctx->contextPriv().makeDeferredRenderTargetContextWithFallback(
	SkBackingFit::kExact,
	kCoverRect.width() + padRight,
	kCoverRect.height() + padBottom,
	kAlpha_8_GrPixelConfig, nullptr));
	if (!maskRTC) {
	return;
	}

	// Draw a checker pattern into the alpha mask so we can visualize the regions left untouched by
	// the clip mask generation.
	this->stencilCheckerboard(maskRTC.get(), true);
	maskRTC->clear(nullptr, GrColorPackA4(0xff), GrRenderTargetContext::CanClearFullscreen::kYes);
	maskRTC->priv().drawAndStencilRect(make_stencil_only_clip(), &GrUserStencilSettings::kUnused,
	SkRegion::kDifference_Op, false, GrAA::kNo, SkMatrix::I(),
	SkRect::MakeIWH(maskRTC->width(), maskRTC->height()));
	reducedClip.drawAlphaClipMask(maskRTC.get());

	int x = kCoverRect.x() - kDeviceRect.x(),
	y = kCoverRect.y() - kDeviceRect.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(maskRTC->asTextureProxyRef(), x, y);
	rtc->drawRect(clip, std::move(paint), GrAA::kYes, SkMatrix::I(),
	SkRect::Make(SkIRect::MakeXYWH(x, y, maskRTC->width(), maskRTC->height())));
	}

	void WindowRectanglesMaskGM::visualizeStencilMask(GrContext* ctx, GrRenderTargetContext* rtc,
	const GrReducedClip& reducedClip,
	GrPaint&& paint) {
	// Draw a checker pattern into the stencil buffer so we can visualize the regions left untouched
	// by the clip mask generation.
	this->stencilCheckerboard(rtc, false);
	reducedClip.drawStencilClipMask(ctx, rtc);

	// Now visualize the stencil mask by covering the entire render target. 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.)
	rtc->drawPaint(make_stencil_only_clip(), std::move(paint), SkMatrix::I());
	}

	void WindowRectanglesMaskGM::stencilCheckerboard(GrRenderTargetContext* rtc, bool flip) {
	constexpr static GrUserStencilSettings kSetClip(
	GrUserStencilSettings::StaticInit<
	0,
	GrUserStencilTest::kAlways,
	0,
	GrUserStencilOp::kSetClipBit,
	GrUserStencilOp::kKeep,
	0>()
	);

	rtc->priv().clearStencilClip(GrFixedClip::Disabled(), false);

	for (int y = 0; y < kDeviceRect.height(); y += kMaskCheckerSize) {
	for (int x = (y & 1) == flip ? 0 : kMaskCheckerSize;
	x < kDeviceRect.width(); x += 2 * kMaskCheckerSize) {
	SkIRect checker = SkIRect::MakeXYWH(x, y, kMaskCheckerSize, kMaskCheckerSize);
	rtc->priv().stencilRect(GrNoClip(), &kSetClip, GrAAType::kNone, 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->drawString(errorMsg, SkIntToScalar(kCoverRect.centerX()),
	SkIntToScalar(kCoverRect.centerY() - 10), paint);
	}

	DEF_GM( return new WindowRectanglesMaskGM(); )

	#endif

	}