tools/viewer/ImageFilterDAGSlide.cpp - skia - Git at Google

 /*
  * Copyright 2019 Google LLC
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include "include/core/SkCanvas.h"
 #include "include/core/SkColor.h"
 #include "include/core/SkColorFilter.h"
 #include "include/core/SkFont.h"
 #include "include/core/SkImage.h"
 #include "include/core/SkImageFilter.h"
 #include "include/core/SkImageInfo.h"
 #include "include/core/SkPaint.h"
 #include "include/core/SkPathEffect.h"
 #include "include/core/SkPoint.h"
 #include "include/core/SkRect.h"
 #include "include/core/SkSurface.h"
 #include "include/effects/SkDashPathEffect.h"
 #include "include/effects/SkGradientShader.h"
 #include "include/effects/SkImageFilters.h"
 #include "src/core/SkImageFilter_Base.h"
 #include "src/core/SkSpecialImage.h"
 #include "tools/ToolUtils.h"
 #include "tools/fonts/FontToolUtils.h"
 #include "tools/viewer/Slide.h"

 namespace {

 struct FilterNode {
     // Pointer to the actual filter in the DAG, so it still contains its input filters and
     // may be used as an input in an earlier node. Null when this represents the "source" input
     sk_sp<SkImageFilter> fFilter;

     // FilterNodes wrapping each of fFilter's inputs. Leaf node when fInputNodes is empty.
     std::vector<FilterNode> fInputNodes;

     // Distance from root filter
     int fDepth;

     // The source content rect (this is the same for all nodes, but is stored here for convenience)
     skif::ParameterSpace<SkRect> fContent;
     // The mapping for the filter dag (same for all nodes, but stored here for convenience)
     skif::Mapping fMapping;

     // Cached reverse bounds using device-space clip bounds (e.g. no local bounds hint passed to
     // saveLayer). This represents the layer calculated in SkCanvas for the filtering.
     skif::LayerSpace<SkIRect> fUnhintedLayerBounds;

     // Cached input bounds using the local draw bounds (e.g. saveLayer with a bounds rect, or
     // an auto-layer for a draw with image filter). This represents the layer bounds up to this
     // point of the DAG.
     skif::LayerSpace<SkIRect> fHintedLayerBounds;

     // Cached output bounds based on local draw bounds. This represents the output up to this
     // point of the DAG.
     skif::LayerSpace<SkIRect> fOutputBounds;

     FilterNode(const SkImageFilter* filter,
                const skif::Mapping& mapping,
                const skif::ParameterSpace<SkRect>& content,
                int depth)
             : fFilter(sk_ref_sp(filter))
             , fDepth(depth)
             , fContent(content)
             , fMapping(mapping) {
         this->computeInputBounds();
         this->computeOutputBounds();
         if (fFilter) {
             fInputNodes.reserve(fFilter->countInputs());
             for (int i = 0; i < fFilter->countInputs(); ++i) {
                 fInputNodes.emplace_back(fFilter->getInput(i), mapping, content, depth + 1);
             }
         }
     }

 private:
     void computeOutputBounds() {
         if (fFilter) {
             // For visualization purposes, we want the output bounds in layer space, before it's
             // been transformed to device space. To achieve that, we mock a new mapping with the
             // identity matrix transform.
             skif::Mapping layerOnly{fMapping.layerMatrix()};
             std::optional<skif::DeviceSpace<SkIRect>> pseudoDeviceBounds =
                     as_IFB(fFilter)->getOutputBounds(layerOnly, fContent);
             // Since layerOnly's device matrix is I, this is effectively a cast to layer space
             if (pseudoDeviceBounds) {
                 fOutputBounds = layerOnly.deviceToLayer(*pseudoDeviceBounds);
             } else {
                 // Skip drawing infinite output bounds
                 fOutputBounds = skif::LayerSpace<SkIRect>::Empty();
             }
         } else {
             fOutputBounds = fMapping.paramToLayer(fContent).roundOut();
         }

         // Fill in children
         for (size_t i = 0; i < fInputNodes.size(); ++i) {
             fInputNodes[i].computeOutputBounds();
         }
     }

     void computeInputBounds() {
         // As a proxy for what the base device had, use the content rect mapped to device space
         // (e.g. clipRect() was called with the same coords prior to the draw).
         skif::DeviceSpace<SkIRect> targetOutput(fMapping.totalMatrix()
                                                         .mapRect(SkRect(fContent))
                                                         .roundOut());

         if (fFilter) {
             fHintedLayerBounds = as_IFB(fFilter)->getInputBounds(fMapping, targetOutput, fContent);
             fUnhintedLayerBounds = as_IFB(fFilter)->getInputBounds(fMapping, targetOutput, {});
         } else {
             fHintedLayerBounds = fMapping.paramToLayer(fContent).roundOut();
             fUnhintedLayerBounds = fMapping.deviceToLayer(targetOutput);
         }
     }
 };

 } // anonymous namespace

 static FilterNode build_dag(const SkMatrix& ctm, const SkRect& rect,
                             const SkImageFilter* rootFilter) {
     // Emulate SkCanvas::internalSaveLayer's decomposition of the CTM.
     skif::ParameterSpace<SkRect> content(rect);
     skif::ParameterSpace<SkPoint> center({rect.centerX(), rect.centerY()});
     skif::Mapping mapping;
     SkAssertResult(mapping.decomposeCTM(ctm, rootFilter, center));
     return FilterNode(rootFilter, mapping, content, 0);
 }

 static void draw_node(SkCanvas* canvas, const FilterNode& node) {
     canvas->clear(SK_ColorTRANSPARENT);

     SkPaint filterPaint;
     filterPaint.setImageFilter(node.fFilter);

     SkRect content = SkRect(node.fContent);
     SkPaint paint;
     static const SkColor kColors[2] = {SK_ColorGREEN, SK_ColorWHITE};
     SkPoint points[2] = { {content.fLeft + 15.f, content.fTop + 15.f},
                           {content.fRight - 15.f, content.fBottom - 15.f} };
     paint.setShader(SkGradientShader::MakeLinear(points, kColors, nullptr, std::size(kColors),
                                                  SkTileMode::kRepeat));

     SkPaint line;
     line.setStrokeWidth(0.f);
     line.setStyle(SkPaint::kStroke_Style);

     canvas->save();
     canvas->concat(node.fMapping.layerToDevice());
     canvas->save();
     canvas->concat(node.fMapping.layerMatrix());

     canvas->saveLayer(&content, &filterPaint);
     canvas->drawRect(content, paint);
     canvas->restore(); // Completes the image filter

     // Draw content-rect bounds
     line.setColor(SK_ColorBLACK);
     canvas->drawRect(content, line);

     // Bounding boxes have all been mapped by the layer matrix from local to layer space, so undo
     // the layer matrix, leaving just the device matrix.
     canvas->restore();

     // The hinted bounds of the layer saved for the filtering
     line.setColor(SK_ColorRED);
     canvas->drawRect(SkRect::Make(SkIRect(node.fHintedLayerBounds)).makeOutset(3.f, 3.f), line);
     // The bounds of the layer if there was no local content hint
     line.setColor(SK_ColorGREEN);
     canvas->drawRect(SkRect::Make(SkIRect(node.fUnhintedLayerBounds)).makeOutset(2.f, 2.f), line);

     // The output bounds in layer space
     line.setColor(SK_ColorBLUE);
     canvas->drawRect(SkRect::Make(SkIRect(node.fOutputBounds)).makeOutset(1.f, 1.f), line);
     // Device-space bounding box of the output bounds (e.g. what legacy DAG manipulation via
     // MatrixTransform would produce).
     static const SkScalar kDashParams[] = {6.f, 12.f};
     line.setPathEffect(SkDashPathEffect::Make(kDashParams, 2, 0.f));
     SkRect devOutputBounds = SkRect::Make(SkIRect(node.fMapping.layerToDevice(node.fOutputBounds)));
     canvas->restore(); // undoes device matrix
     canvas->drawRect(devOutputBounds, line);
 }

 static constexpr float kLineHeight = 16.f;
 static constexpr float kLineInset = 8.f;

 static float print_matrix(SkCanvas* canvas, const char* prefix, const SkMatrix& matrix,
                          float x, float y, const SkFont& font, const SkPaint& paint) {
     canvas->drawString(prefix, x, y, font, paint);
     y += kLineHeight;
     for (int i = 0; i < 3; ++i) {
         SkString row;
         row.appendf("[%.2f %.2f %.2f]",
                     matrix.get(i * 3), matrix.get(i * 3 + 1), matrix.get(i * 3 + 2));
         canvas->drawString(row, x, y, font, paint);
         y += kLineHeight;
     }
     return y;
 }

 static float print_size(SkCanvas* canvas, const char* prefix, const SkIRect& rect,
                        float x, float y, const SkFont& font, const SkPaint& paint) {
     canvas->drawString(prefix, x, y, font, paint);
     y += kLineHeight;
     SkString sz;
     sz.appendf("%d x %d", rect.width(), rect.height());
     canvas->drawString(sz, x, y, font, paint);
     return y + kLineHeight;
 }

 static float print_info(SkCanvas* canvas, const FilterNode& node) {
     SkFont font(ToolUtils::DefaultTypeface(), 12);
     SkPaint text;
     text.setAntiAlias(true);

     float y = kLineHeight;
     if (node.fFilter) {
         canvas->drawString(node.fFilter->getTypeName(), kLineInset, y, font, text);
         y += kLineHeight;
         if (node.fDepth == 0) {
             // The mapping is the same for all nodes, so only print at the root
             y = print_matrix(canvas, "Param->Layer", node.fMapping.layerMatrix(),
                         kLineInset, y, font, text);
             y = print_matrix(canvas,
                              "Layer->Device",
                              node.fMapping.layerToDevice(),
                              kLineInset,
                              y,
                              font,
                              text);
         }

         y = print_size(canvas, "Layer Size", SkIRect(node.fUnhintedLayerBounds),
                        kLineInset, y, font, text);
         y = print_size(canvas, "Layer Size (hinted)", SkIRect(node.fHintedLayerBounds),
                        kLineInset, y, font, text);
     } else {
         canvas->drawString("Source Input", kLineInset, y, font, text);
         y += kLineHeight;
     }

     return y;
 }

 // Returns bottom edge in pixels that the subtree reached in canvas
 static float draw_dag(SkCanvas* canvas, SkSurface* nodeSurface, const FilterNode& node) {
     // First capture the results of the node, into nodeSurface
     draw_node(nodeSurface->getCanvas(), node);
     sk_sp<SkImage> nodeResults = nodeSurface->makeImageSnapshot();

     // Fill in background of the filter node with a checkerboard
     canvas->save();
     canvas->clipRect(SkRect::MakeWH(nodeResults->width(), nodeResults->height()));
     ToolUtils::draw_checkerboard(canvas, SK_ColorGRAY, SK_ColorLTGRAY, 10);
     canvas->restore();

     // Display filtered results in current canvas' location (assumed CTM is set for this node)
     canvas->drawImage(nodeResults, 0, 0);

     SkPaint line;
     line.setAntiAlias(true);
     line.setStyle(SkPaint::kStroke_Style);
     line.setStrokeWidth(3.f);

     // Text info
     canvas->save();
     canvas->translate(0, nodeResults->height());
     float textHeight = print_info(canvas, node);
     canvas->restore();

     // Border around filtered results + text info
     canvas->drawRect(SkRect::MakeWH(nodeResults->width(), nodeResults->height() + textHeight),
                      line);

     static const float kPad = 20.f;
     float x = nodeResults->width() + kPad;
     float y = 0;
     for (size_t i = 0; i < node.fInputNodes.size(); ++i) {
         // Line connecting this node to its child
         canvas->drawLine(nodeResults->width(), 0.5f * nodeResults->height(), // right of node
                          x, y + 0.5f * nodeResults->height(), line);         // left of child
         canvas->save();
         canvas->translate(x, y);
         y += draw_dag(canvas, nodeSurface, node.fInputNodes[i]);
         canvas->restore();
     }
     return std::max(y, nodeResults->height() + textHeight + kPad);
 }

 static void draw_dag(SkCanvas* canvas, SkImageFilter* filter,
                      const SkRect& rect, const SkISize& surfaceSize) {
     // Get the current CTM, which includes all the viewer's UI modifications, which we want to
     // pass into our mock canvases for each DAG node.
     SkMatrix ctm = canvas->getTotalMatrix();

     canvas->save();
     // Reset the matrix so that the DAG layout and instructional text is fixed to the window.
     canvas->resetMatrix();

     // Process the image filter DAG to display intermediate results later on, which will apply the
     // provided CTM during draw_node calls.
     FilterNode dag = build_dag(ctm, rect, filter);

     sk_sp<SkSurface> nodeSurface =
             canvas->makeSurface(canvas->imageInfo().makeDimensions(surfaceSize));
     draw_dag(canvas, nodeSurface.get(), dag);

     canvas->restore();
 }

 class ImageFilterDAGSlide : public Slide {
 public:
     ImageFilterDAGSlide() { fName = "ImageFilterDAG"; }

     void draw(SkCanvas* canvas) override {
         // Make a large DAG
         //        /--- Color Filter <---- Blur <--- Offset
         // Merge <
         //        \--- Blur <--- Drop Shadow
         sk_sp<SkImageFilter> drop2 = SkImageFilters::DropShadow(
                 10.f, 5.f, 3.f, 3.f, SK_ColorBLACK, nullptr);
         sk_sp<SkImageFilter> blur1 = SkImageFilters::Blur(2.f, 2.f, std::move(drop2));

         sk_sp<SkImageFilter> offset3 = SkImageFilters::Offset(-5.f, -5.f, nullptr);
         sk_sp<SkImageFilter> blur2 = SkImageFilters::Blur(4.f, 4.f, std::move(offset3));
         sk_sp<SkImageFilter> cf1 = SkImageFilters::ColorFilter(
                 SkColorFilters::Blend(SK_ColorGRAY, SkBlendMode::kModulate), std::move(blur2));

         sk_sp<SkImageFilter> merge0 = SkImageFilters::Merge(std::move(blur1), std::move(cf1));

         draw_dag(canvas, merge0.get(), kFilterRect, kFilterSurfaceSize);
     }

     // We want to use the viewer calculated CTM in the mini surfaces used per DAG node. The rotation
     // matrix viewer calculates is based on the slide content size.
     SkISize getDimensions() const override { return kFilterSurfaceSize; }

 private:
     static constexpr SkRect kFilterRect = SkRect::MakeXYWH(20.f, 20.f, 60.f, 60.f);
     static constexpr SkISize kFilterSurfaceSize = SkISize::Make(
             2 * (kFilterRect.fRight + kFilterRect.fLeft),
             2 * (kFilterRect.fBottom + kFilterRect.fTop));

 };

 DEF_SLIDE(return new ImageFilterDAGSlide();)
	/*
	* Copyright 2019 Google LLC
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#include "include/core/SkCanvas.h"
	#include "include/core/SkColor.h"
	#include "include/core/SkColorFilter.h"
	#include "include/core/SkFont.h"
	#include "include/core/SkImage.h"
	#include "include/core/SkImageFilter.h"
	#include "include/core/SkImageInfo.h"
	#include "include/core/SkPaint.h"
	#include "include/core/SkPathEffect.h"
	#include "include/core/SkPoint.h"
	#include "include/core/SkRect.h"
	#include "include/core/SkSurface.h"
	#include "include/effects/SkDashPathEffect.h"
	#include "include/effects/SkGradientShader.h"
	#include "include/effects/SkImageFilters.h"
	#include "src/core/SkImageFilter_Base.h"
	#include "src/core/SkSpecialImage.h"
	#include "tools/ToolUtils.h"
	#include "tools/fonts/FontToolUtils.h"
	#include "tools/viewer/Slide.h"

	namespace {

	struct FilterNode {
	// Pointer to the actual filter in the DAG, so it still contains its input filters and
	// may be used as an input in an earlier node. Null when this represents the "source" input
	sk_sp<SkImageFilter> fFilter;

	// FilterNodes wrapping each of fFilter's inputs. Leaf node when fInputNodes is empty.
	std::vector<FilterNode> fInputNodes;

	// Distance from root filter
	int fDepth;

	// The source content rect (this is the same for all nodes, but is stored here for convenience)
	skif::ParameterSpace<SkRect> fContent;
	// The mapping for the filter dag (same for all nodes, but stored here for convenience)
	skif::Mapping fMapping;

	// Cached reverse bounds using device-space clip bounds (e.g. no local bounds hint passed to
	// saveLayer). This represents the layer calculated in SkCanvas for the filtering.
	skif::LayerSpace<SkIRect> fUnhintedLayerBounds;

	// Cached input bounds using the local draw bounds (e.g. saveLayer with a bounds rect, or
	// an auto-layer for a draw with image filter). This represents the layer bounds up to this
	// point of the DAG.
	skif::LayerSpace<SkIRect> fHintedLayerBounds;

	// Cached output bounds based on local draw bounds. This represents the output up to this
	// point of the DAG.
	skif::LayerSpace<SkIRect> fOutputBounds;

	FilterNode(const SkImageFilter* filter,
	const skif::Mapping& mapping,
	const skif::ParameterSpace<SkRect>& content,
	int depth)
	: fFilter(sk_ref_sp(filter))
	, fDepth(depth)
	, fContent(content)
	, fMapping(mapping) {
	this->computeInputBounds();
	this->computeOutputBounds();
	if (fFilter) {
	fInputNodes.reserve(fFilter->countInputs());
	for (int i = 0; i < fFilter->countInputs(); ++i) {
	fInputNodes.emplace_back(fFilter->getInput(i), mapping, content, depth + 1);
	}
	}
	}

	private:
	void computeOutputBounds() {
	if (fFilter) {
	// For visualization purposes, we want the output bounds in layer space, before it's
	// been transformed to device space. To achieve that, we mock a new mapping with the
	// identity matrix transform.
	skif::Mapping layerOnly{fMapping.layerMatrix()};
	std::optional<skif::DeviceSpace<SkIRect>> pseudoDeviceBounds =
	as_IFB(fFilter)->getOutputBounds(layerOnly, fContent);
	// Since layerOnly's device matrix is I, this is effectively a cast to layer space
	if (pseudoDeviceBounds) {
	fOutputBounds = layerOnly.deviceToLayer(*pseudoDeviceBounds);
	} else {
	// Skip drawing infinite output bounds
	fOutputBounds = skif::LayerSpace<SkIRect>::Empty();
	}
	} else {
	fOutputBounds = fMapping.paramToLayer(fContent).roundOut();
	}

	// Fill in children
	for (size_t i = 0; i < fInputNodes.size(); ++i) {
	fInputNodes[i].computeOutputBounds();
	}
	}

	void computeInputBounds() {
	// As a proxy for what the base device had, use the content rect mapped to device space
	// (e.g. clipRect() was called with the same coords prior to the draw).
	skif::DeviceSpace<SkIRect> targetOutput(fMapping.totalMatrix()
	.mapRect(SkRect(fContent))
	.roundOut());

	if (fFilter) {
	fHintedLayerBounds = as_IFB(fFilter)->getInputBounds(fMapping, targetOutput, fContent);
	fUnhintedLayerBounds = as_IFB(fFilter)->getInputBounds(fMapping, targetOutput, {});
	} else {
	fHintedLayerBounds = fMapping.paramToLayer(fContent).roundOut();
	fUnhintedLayerBounds = fMapping.deviceToLayer(targetOutput);
	}
	}
	};

	} // anonymous namespace

	static FilterNode build_dag(const SkMatrix& ctm, const SkRect& rect,
	const SkImageFilter* rootFilter) {
	// Emulate SkCanvas::internalSaveLayer's decomposition of the CTM.
	skif::ParameterSpace<SkRect> content(rect);
	skif::ParameterSpace<SkPoint> center({rect.centerX(), rect.centerY()});
	skif::Mapping mapping;
	SkAssertResult(mapping.decomposeCTM(ctm, rootFilter, center));
	return FilterNode(rootFilter, mapping, content, 0);
	}

	static void draw_node(SkCanvas* canvas, const FilterNode& node) {
	canvas->clear(SK_ColorTRANSPARENT);

	SkPaint filterPaint;
	filterPaint.setImageFilter(node.fFilter);

	SkRect content = SkRect(node.fContent);
	SkPaint paint;
	static const SkColor kColors[2] = {SK_ColorGREEN, SK_ColorWHITE};
	SkPoint points[2] = { {content.fLeft + 15.f, content.fTop + 15.f},
	{content.fRight - 15.f, content.fBottom - 15.f} };
	paint.setShader(SkGradientShader::MakeLinear(points, kColors, nullptr, std::size(kColors),
	SkTileMode::kRepeat));

	SkPaint line;
	line.setStrokeWidth(0.f);
	line.setStyle(SkPaint::kStroke_Style);

	canvas->save();
	canvas->concat(node.fMapping.layerToDevice());
	canvas->save();
	canvas->concat(node.fMapping.layerMatrix());

	canvas->saveLayer(&content, &filterPaint);
	canvas->drawRect(content, paint);
	canvas->restore(); // Completes the image filter

	// Draw content-rect bounds
	line.setColor(SK_ColorBLACK);
	canvas->drawRect(content, line);

	// Bounding boxes have all been mapped by the layer matrix from local to layer space, so undo
	// the layer matrix, leaving just the device matrix.
	canvas->restore();

	// The hinted bounds of the layer saved for the filtering
	line.setColor(SK_ColorRED);
	canvas->drawRect(SkRect::Make(SkIRect(node.fHintedLayerBounds)).makeOutset(3.f, 3.f), line);
	// The bounds of the layer if there was no local content hint
	line.setColor(SK_ColorGREEN);
	canvas->drawRect(SkRect::Make(SkIRect(node.fUnhintedLayerBounds)).makeOutset(2.f, 2.f), line);

	// The output bounds in layer space
	line.setColor(SK_ColorBLUE);
	canvas->drawRect(SkRect::Make(SkIRect(node.fOutputBounds)).makeOutset(1.f, 1.f), line);
	// Device-space bounding box of the output bounds (e.g. what legacy DAG manipulation via
	// MatrixTransform would produce).
	static const SkScalar kDashParams[] = {6.f, 12.f};
	line.setPathEffect(SkDashPathEffect::Make(kDashParams, 2, 0.f));
	SkRect devOutputBounds = SkRect::Make(SkIRect(node.fMapping.layerToDevice(node.fOutputBounds)));
	canvas->restore(); // undoes device matrix
	canvas->drawRect(devOutputBounds, line);
	}

	static constexpr float kLineHeight = 16.f;
	static constexpr float kLineInset = 8.f;

	static float print_matrix(SkCanvas* canvas, const char* prefix, const SkMatrix& matrix,
	float x, float y, const SkFont& font, const SkPaint& paint) {
	canvas->drawString(prefix, x, y, font, paint);
	y += kLineHeight;
	for (int i = 0; i < 3; ++i) {
	SkString row;
	row.appendf("[%.2f %.2f %.2f]",
	matrix.get(i * 3), matrix.get(i * 3 + 1), matrix.get(i * 3 + 2));
	canvas->drawString(row, x, y, font, paint);
	y += kLineHeight;
	}
	return y;
	}

	static float print_size(SkCanvas* canvas, const char* prefix, const SkIRect& rect,
	float x, float y, const SkFont& font, const SkPaint& paint) {
	canvas->drawString(prefix, x, y, font, paint);
	y += kLineHeight;
	SkString sz;
	sz.appendf("%d x %d", rect.width(), rect.height());
	canvas->drawString(sz, x, y, font, paint);
	return y + kLineHeight;
	}

	static float print_info(SkCanvas* canvas, const FilterNode& node) {
	SkFont font(ToolUtils::DefaultTypeface(), 12);
	SkPaint text;
	text.setAntiAlias(true);

	float y = kLineHeight;
	if (node.fFilter) {
	canvas->drawString(node.fFilter->getTypeName(), kLineInset, y, font, text);
	y += kLineHeight;
	if (node.fDepth == 0) {
	// The mapping is the same for all nodes, so only print at the root
	y = print_matrix(canvas, "Param->Layer", node.fMapping.layerMatrix(),
	kLineInset, y, font, text);
	y = print_matrix(canvas,
	"Layer->Device",
	node.fMapping.layerToDevice(),
	kLineInset,
	y,
	font,
	text);
	}

	y = print_size(canvas, "Layer Size", SkIRect(node.fUnhintedLayerBounds),
	kLineInset, y, font, text);
	y = print_size(canvas, "Layer Size (hinted)", SkIRect(node.fHintedLayerBounds),
	kLineInset, y, font, text);
	} else {
	canvas->drawString("Source Input", kLineInset, y, font, text);
	y += kLineHeight;
	}

	return y;
	}

	// Returns bottom edge in pixels that the subtree reached in canvas
	static float draw_dag(SkCanvas* canvas, SkSurface* nodeSurface, const FilterNode& node) {
	// First capture the results of the node, into nodeSurface
	draw_node(nodeSurface->getCanvas(), node);
	sk_sp<SkImage> nodeResults = nodeSurface->makeImageSnapshot();

	// Fill in background of the filter node with a checkerboard
	canvas->save();
	canvas->clipRect(SkRect::MakeWH(nodeResults->width(), nodeResults->height()));
	ToolUtils::draw_checkerboard(canvas, SK_ColorGRAY, SK_ColorLTGRAY, 10);
	canvas->restore();

	// Display filtered results in current canvas' location (assumed CTM is set for this node)
	canvas->drawImage(nodeResults, 0, 0);

	SkPaint line;
	line.setAntiAlias(true);
	line.setStyle(SkPaint::kStroke_Style);
	line.setStrokeWidth(3.f);

	// Text info
	canvas->save();
	canvas->translate(0, nodeResults->height());
	float textHeight = print_info(canvas, node);
	canvas->restore();

	// Border around filtered results + text info
	canvas->drawRect(SkRect::MakeWH(nodeResults->width(), nodeResults->height() + textHeight),
	line);

	static const float kPad = 20.f;
	float x = nodeResults->width() + kPad;
	float y = 0;
	for (size_t i = 0; i < node.fInputNodes.size(); ++i) {
	// Line connecting this node to its child
	canvas->drawLine(nodeResults->width(), 0.5f * nodeResults->height(), // right of node
	x, y + 0.5f * nodeResults->height(), line); // left of child
	canvas->save();
	canvas->translate(x, y);
	y += draw_dag(canvas, nodeSurface, node.fInputNodes[i]);
	canvas->restore();
	}
	return std::max(y, nodeResults->height() + textHeight + kPad);
	}

	static void draw_dag(SkCanvas* canvas, SkImageFilter* filter,
	const SkRect& rect, const SkISize& surfaceSize) {
	// Get the current CTM, which includes all the viewer's UI modifications, which we want to
	// pass into our mock canvases for each DAG node.
	SkMatrix ctm = canvas->getTotalMatrix();

	canvas->save();
	// Reset the matrix so that the DAG layout and instructional text is fixed to the window.
	canvas->resetMatrix();

	// Process the image filter DAG to display intermediate results later on, which will apply the
	// provided CTM during draw_node calls.
	FilterNode dag = build_dag(ctm, rect, filter);

	sk_sp<SkSurface> nodeSurface =
	canvas->makeSurface(canvas->imageInfo().makeDimensions(surfaceSize));
	draw_dag(canvas, nodeSurface.get(), dag);

	canvas->restore();
	}

	class ImageFilterDAGSlide : public Slide {
	public:
	ImageFilterDAGSlide() { fName = "ImageFilterDAG"; }

	void draw(SkCanvas* canvas) override {
	// Make a large DAG
	// /--- Color Filter <---- Blur <--- Offset
	// Merge <
	// \--- Blur <--- Drop Shadow
	sk_sp<SkImageFilter> drop2 = SkImageFilters::DropShadow(
	10.f, 5.f, 3.f, 3.f, SK_ColorBLACK, nullptr);
	sk_sp<SkImageFilter> blur1 = SkImageFilters::Blur(2.f, 2.f, std::move(drop2));

	sk_sp<SkImageFilter> offset3 = SkImageFilters::Offset(-5.f, -5.f, nullptr);
	sk_sp<SkImageFilter> blur2 = SkImageFilters::Blur(4.f, 4.f, std::move(offset3));
	sk_sp<SkImageFilter> cf1 = SkImageFilters::ColorFilter(
	SkColorFilters::Blend(SK_ColorGRAY, SkBlendMode::kModulate), std::move(blur2));

	sk_sp<SkImageFilter> merge0 = SkImageFilters::Merge(std::move(blur1), std::move(cf1));

	draw_dag(canvas, merge0.get(), kFilterRect, kFilterSurfaceSize);
	}

	// We want to use the viewer calculated CTM in the mini surfaces used per DAG node. The rotation
	// matrix viewer calculates is based on the slide content size.
	SkISize getDimensions() const override { return kFilterSurfaceSize; }

	private:
	static constexpr SkRect kFilterRect = SkRect::MakeXYWH(20.f, 20.f, 60.f, 60.f);
	static constexpr SkISize kFilterSurfaceSize = SkISize::Make(
	2 * (kFilterRect.fRight + kFilterRect.fLeft),
	2 * (kFilterRect.fBottom + kFilterRect.fTop));

	};

	DEF_SLIDE(return new ImageFilterDAGSlide();)