src/core/SkLinearBitmapPipeline_core.h - skia - Git at Google

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #ifndef SkLinearBitmapPipeline_core_DEFINED
 #define SkLinearBitmapPipeline_core_DEFINED

 #include <algorithm>
 #include <cmath>
 #include "SkNx.h"

 // New bilerp strategy:
 // Pass through on bilerpList4 and bilerpListFew (analogs to pointList), introduce bilerpEdge
 // which takes 4 points. If the sample spans an edge, then break it into a bilerpEdge. Bilerp
 // span then becomes a normal span except in special cases where an extra Y is given. The bilerp
 // need to stay single point calculations until the tile layer.
 // TODO:
 //  - edge span predicate.
 //  - introduce new point API
 //  - Add tile for new api.

 namespace {
 struct X {
     explicit X(SkScalar val) : fVal{val} { }
     explicit X(SkPoint pt)   : fVal{pt.fX} { }
     explicit X(SkSize s)     : fVal{s.fWidth} { }
     explicit X(SkISize s)    : fVal((SkScalar)s.fWidth) { }
     operator SkScalar () const {return fVal;}
 private:
     SkScalar fVal;
 };

 struct Y {
     explicit Y(SkScalar val) : fVal{val} { }
     explicit Y(SkPoint pt)   : fVal{pt.fY} { }
     explicit Y(SkSize s)     : fVal{s.fHeight} { }
     explicit Y(SkISize s)    : fVal((SkScalar)s.fHeight) { }
     operator SkScalar () const {return fVal;}
 private:
     SkScalar fVal;
 };

 // The Span class enables efficient processing horizontal spans of pixels.
 // * start - the point where to start the span.
 // * length - the number of pixels to traverse in source space.
 // * count - the number of pixels to produce in destination space.
 // Both start and length are mapped through the inversion matrix to produce values in source
 // space. After the matrix operation, the tilers may break the spans up into smaller spans.
 // The tilers can produce spans that seem nonsensical.
 // * The clamp tiler can create spans with length of 0. This indicates to copy an edge pixel out
 //   to the edge of the destination scan.
 // * The mirror tiler can produce spans with negative length. This indicates that the source
 //   should be traversed in the opposite direction to the destination pixels.
 class Span {
 public:
     Span(SkPoint start, SkScalar length, int count)
         : fStart(start)
         , fLength(length)
         , fCount{count} {
         SkASSERT(std::isfinite(length));
     }

     operator std::tuple<SkPoint&, SkScalar&, int&>() {
         return std::tie(fStart, fLength, fCount);
     }

     bool isEmpty() const { return 0 == fCount; }
     void clear() { fCount = 0; }
     int count() const { return fCount; }
     SkScalar length() const { return fLength; }
     SkScalar startX() const { return X(fStart); }
     SkScalar endX() const { return this->startX() + this->length(); }
     SkScalar startY() const { return Y(fStart); }
     Span emptySpan() { return Span{{0.0, 0.0}, 0.0f, 0}; }

     bool completelyWithin(SkScalar xMin, SkScalar xMax) const {
         SkScalar sMin, sMax;
         std::tie(sMin, sMax) = std::minmax(startX(), endX());
         return xMin <= sMin && sMax < xMax;
     }

     void offset(SkScalar offsetX) {
         fStart.offset(offsetX, 0.0f);
     }

     Span breakAt(SkScalar breakX, SkScalar dx) {
         SkASSERT(std::isfinite(breakX));
         SkASSERT(std::isfinite(dx));
         SkASSERT(dx != 0.0f);

         if (this->isEmpty()) {
             return this->emptySpan();
         }

         int dxSteps = SkScalarFloorToInt((breakX - this->startX()) / dx);

         if (dxSteps < 0) {
             // The span is wholly after breakX.
             return this->emptySpan();
         } else if (dxSteps >= fCount) {
             // The span is wholly before breakX.
             Span answer = *this;
             this->clear();
             return answer;
         }

         // Calculate the values for the span to cleave off.
         SkScalar newLength = dxSteps * dx;

         // If the last (or first if count = 1) sample lands directly on the boundary. Include it
         // when dx < 0 and exclude it when dx > 0.
         // Reasoning:
         //  dx > 0: The sample point on the boundary is part of the next span because the entire
         // pixel is after the boundary.
         //  dx < 0: The sample point on the boundary is part of the current span because the
         // entire pixel is before the boundary.
         if (this->startX() + newLength == breakX && dx > 0) {
             if (dxSteps > 0) {
                 dxSteps -= 1;
                 newLength -= dx;
             } else {
                 return this->emptySpan();
             }
         }

         // Calculate new span parameters
         SkPoint newStart = fStart;
         int newCount = dxSteps + 1;
         SkASSERT(newCount > 0);

         // Update this span to reflect the break.
         SkScalar lengthToStart = newLength + dx;
         fLength -= lengthToStart;
         fCount -= newCount;
         fStart = {this->startX() + lengthToStart, Y(fStart)};

         return Span{newStart, newLength, newCount};
     }

     void clampToSinglePixel(SkPoint pixel) {
         fStart = pixel;
         fLength = 0.0f;
     }

 private:
     SkPoint  fStart;
     SkScalar fLength;
     int      fCount;
 };

 template<typename Stage>
 void span_fallback(Span span, Stage* stage) {
     SkPoint start;
     SkScalar length;
     int count;
     std::tie(start, length, count) = span;
     Sk4f startXs{X(start)};
     Sk4f ys{Y(start)};
     Sk4f mults = {0.0f, 1.0f, 2.0f, 3.0f};

     // Initializing this is not needed, but some compilers can't figure this out.
     Sk4s dXs{0.0f};
     if (count > 1) {
         SkScalar dx = length / (count - 1);
         dXs = Sk4f{dx};
     }

     // Instead of using xs = xs + dx every round, this uses xs = i * dx + X(start). This
     // eliminates the rounding error for the sum.
     Sk4f xs = startXs + mults * dXs;
     while (count >= 4) {
         stage->pointList4(xs, ys);

         mults += Sk4f{4.0f};
         xs = mults * dXs + startXs;
         count -= 4;
     }

     if (count > 0) {
         stage->pointListFew(count, xs, ys);
     }
 }

 inline Sk4f SK_VECTORCALL check_pixel(const Sk4f& pixel) {
     SkASSERTF(0.0f <= pixel[0] && pixel[0] <= 1.0f, "pixel[0]: %f", pixel[0]);
     SkASSERTF(0.0f <= pixel[1] && pixel[1] <= 1.0f, "pixel[1]: %f", pixel[1]);
     SkASSERTF(0.0f <= pixel[2] && pixel[2] <= 1.0f, "pixel[2]: %f", pixel[2]);
     SkASSERTF(0.0f <= pixel[3] && pixel[3] <= 1.0f, "pixel[3]: %f", pixel[3]);
     return pixel;
 }

 }  // namespace

 class SkLinearBitmapPipeline::PointProcessorInterface {
 public:
     virtual ~PointProcessorInterface() { }
     // Take the first n (where 0 < n && n < 4) items from xs and ys and sample those points. For
     // nearest neighbor, that means just taking the floor xs and ys. For bilerp, this means
     // to expand the bilerp filter around the point and sample using that filter.
     virtual void SK_VECTORCALL pointListFew(int n, Sk4s xs, Sk4s ys) = 0;
     // Same as pointListFew, but n = 4.
     virtual void SK_VECTORCALL pointList4(Sk4s xs, Sk4s ys) = 0;
     // A span is a compact form of sample points that are obtained by mapping points from
     // destination space to source space. This is used for horizontal lines only, and is mainly
     // used to take advantage of memory coherence for horizontal spans.
     virtual void pointSpan(Span span) = 0;
 };

 class SkLinearBitmapPipeline::SampleProcessorInterface
     : public SkLinearBitmapPipeline::PointProcessorInterface {
 public:
     // Used for nearest neighbor when scale factor is 1.0. The span can just be repeated with no
     // edge pixel alignment problems. This is for handling a very common case.
     virtual void repeatSpan(Span span, int32_t repeatCount) = 0;
 };

 class SkLinearBitmapPipeline::DestinationInterface {
 public:
     virtual ~DestinationInterface() { }
     // Count is normally not needed, but in these early stages of development it is useful to
     // check bounds.
     // TODO(herb): 4/6/2016 - remove count when code is stable.
     virtual void setDestination(void* dst, int count) = 0;
 };

 class SkLinearBitmapPipeline::BlendProcessorInterface
     : public SkLinearBitmapPipeline::DestinationInterface {
 public:
     virtual void SK_VECTORCALL blendPixel(Sk4f pixel0) = 0;
     virtual void SK_VECTORCALL blend4Pixels(Sk4f p0, Sk4f p1, Sk4f p2, Sk4f p3) = 0;
 };

 class SkLinearBitmapPipeline::PixelAccessorInterface {
 public:
     virtual ~PixelAccessorInterface() { }
     virtual void SK_VECTORCALL getFewPixels(
         int n, Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2) const = 0;

     virtual void SK_VECTORCALL get4Pixels(
         Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const = 0;

     virtual void get4Pixels(
         const void* src, int index, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const = 0;

     virtual Sk4f getPixelFromRow(const void* row, int index) const = 0;

     virtual Sk4f getPixelAt(int index) const = 0;

     virtual const void* row(int y) const = 0;
 };

 #endif // SkLinearBitmapPipeline_core_DEFINED
	/*
	* Copyright 2016 Google Inc.
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#ifndef SkLinearBitmapPipeline_core_DEFINED
	#define SkLinearBitmapPipeline_core_DEFINED

	#include <algorithm>
	#include <cmath>
	#include "SkNx.h"

	// New bilerp strategy:
	// Pass through on bilerpList4 and bilerpListFew (analogs to pointList), introduce bilerpEdge
	// which takes 4 points. If the sample spans an edge, then break it into a bilerpEdge. Bilerp
	// span then becomes a normal span except in special cases where an extra Y is given. The bilerp
	// need to stay single point calculations until the tile layer.
	// TODO:
	// - edge span predicate.
	// - introduce new point API
	// - Add tile for new api.

	namespace {
	struct X {
	explicit X(SkScalar val) : fVal{val} { }
	explicit X(SkPoint pt) : fVal{pt.fX} { }
	explicit X(SkSize s) : fVal{s.fWidth} { }
	explicit X(SkISize s) : fVal((SkScalar)s.fWidth) { }
	operator SkScalar () const {return fVal;}
	private:
	SkScalar fVal;
	};

	struct Y {
	explicit Y(SkScalar val) : fVal{val} { }
	explicit Y(SkPoint pt) : fVal{pt.fY} { }
	explicit Y(SkSize s) : fVal{s.fHeight} { }
	explicit Y(SkISize s) : fVal((SkScalar)s.fHeight) { }
	operator SkScalar () const {return fVal;}
	private:
	SkScalar fVal;
	};

	// The Span class enables efficient processing horizontal spans of pixels.
	// * start - the point where to start the span.
	// * length - the number of pixels to traverse in source space.
	// * count - the number of pixels to produce in destination space.
	// Both start and length are mapped through the inversion matrix to produce values in source
	// space. After the matrix operation, the tilers may break the spans up into smaller spans.
	// The tilers can produce spans that seem nonsensical.
	// * The clamp tiler can create spans with length of 0. This indicates to copy an edge pixel out
	// to the edge of the destination scan.
	// * The mirror tiler can produce spans with negative length. This indicates that the source
	// should be traversed in the opposite direction to the destination pixels.
	class Span {
	public:
	Span(SkPoint start, SkScalar length, int count)
	: fStart(start)
	, fLength(length)
	, fCount{count} {
	SkASSERT(std::isfinite(length));
	}

	operator std::tuple<SkPoint&, SkScalar&, int&>() {
	return std::tie(fStart, fLength, fCount);
	}

	bool isEmpty() const { return 0 == fCount; }
	void clear() { fCount = 0; }
	int count() const { return fCount; }
	SkScalar length() const { return fLength; }
	SkScalar startX() const { return X(fStart); }
	SkScalar endX() const { return this->startX() + this->length(); }
	SkScalar startY() const { return Y(fStart); }
	Span emptySpan() { return Span{{0.0, 0.0}, 0.0f, 0}; }

	bool completelyWithin(SkScalar xMin, SkScalar xMax) const {
	SkScalar sMin, sMax;
	std::tie(sMin, sMax) = std::minmax(startX(), endX());
	return xMin <= sMin && sMax < xMax;
	}

	void offset(SkScalar offsetX) {
	fStart.offset(offsetX, 0.0f);
	}

	Span breakAt(SkScalar breakX, SkScalar dx) {
	SkASSERT(std::isfinite(breakX));
	SkASSERT(std::isfinite(dx));
	SkASSERT(dx != 0.0f);

	if (this->isEmpty()) {
	return this->emptySpan();
	}

	int dxSteps = SkScalarFloorToInt((breakX - this->startX()) / dx);

	if (dxSteps < 0) {
	// The span is wholly after breakX.
	return this->emptySpan();
	} else if (dxSteps >= fCount) {
	// The span is wholly before breakX.
	Span answer = *this;
	this->clear();
	return answer;
	}

	// Calculate the values for the span to cleave off.
	SkScalar newLength = dxSteps * dx;

	// If the last (or first if count = 1) sample lands directly on the boundary. Include it
	// when dx < 0 and exclude it when dx > 0.
	// Reasoning:
	// dx > 0: The sample point on the boundary is part of the next span because the entire
	// pixel is after the boundary.
	// dx < 0: The sample point on the boundary is part of the current span because the
	// entire pixel is before the boundary.
	if (this->startX() + newLength == breakX && dx > 0) {
	if (dxSteps > 0) {
	dxSteps -= 1;
	newLength -= dx;
	} else {
	return this->emptySpan();
	}
	}

	// Calculate new span parameters
	SkPoint newStart = fStart;
	int newCount = dxSteps + 1;
	SkASSERT(newCount > 0);

	// Update this span to reflect the break.
	SkScalar lengthToStart = newLength + dx;
	fLength -= lengthToStart;
	fCount -= newCount;
	fStart = {this->startX() + lengthToStart, Y(fStart)};

	return Span{newStart, newLength, newCount};
	}

	void clampToSinglePixel(SkPoint pixel) {
	fStart = pixel;
	fLength = 0.0f;
	}

	private:
	SkPoint fStart;
	SkScalar fLength;
	int fCount;
	};

	template<typename Stage>
	void span_fallback(Span span, Stage* stage) {
	SkPoint start;
	SkScalar length;
	int count;
	std::tie(start, length, count) = span;
	Sk4f startXs{X(start)};
	Sk4f ys{Y(start)};
	Sk4f mults = {0.0f, 1.0f, 2.0f, 3.0f};

	// Initializing this is not needed, but some compilers can't figure this out.
	Sk4s dXs{0.0f};
	if (count > 1) {
	SkScalar dx = length / (count - 1);
	dXs = Sk4f{dx};
	}

	// Instead of using xs = xs + dx every round, this uses xs = i * dx + X(start). This
	// eliminates the rounding error for the sum.
	Sk4f xs = startXs + mults * dXs;
	while (count >= 4) {
	stage->pointList4(xs, ys);

	mults += Sk4f{4.0f};
	xs = mults * dXs + startXs;
	count -= 4;
	}

	if (count > 0) {
	stage->pointListFew(count, xs, ys);
	}
	}

	inline Sk4f SK_VECTORCALL check_pixel(const Sk4f& pixel) {
	SkASSERTF(0.0f <= pixel[0] && pixel[0] <= 1.0f, "pixel[0]: %f", pixel[0]);
	SkASSERTF(0.0f <= pixel[1] && pixel[1] <= 1.0f, "pixel[1]: %f", pixel[1]);
	SkASSERTF(0.0f <= pixel[2] && pixel[2] <= 1.0f, "pixel[2]: %f", pixel[2]);
	SkASSERTF(0.0f <= pixel[3] && pixel[3] <= 1.0f, "pixel[3]: %f", pixel[3]);
	return pixel;
	}

	} // namespace

	class SkLinearBitmapPipeline::PointProcessorInterface {
	public:
	virtual ~PointProcessorInterface() { }
	// Take the first n (where 0 < n && n < 4) items from xs and ys and sample those points. For
	// nearest neighbor, that means just taking the floor xs and ys. For bilerp, this means
	// to expand the bilerp filter around the point and sample using that filter.
	virtual void SK_VECTORCALL pointListFew(int n, Sk4s xs, Sk4s ys) = 0;
	// Same as pointListFew, but n = 4.
	virtual void SK_VECTORCALL pointList4(Sk4s xs, Sk4s ys) = 0;
	// A span is a compact form of sample points that are obtained by mapping points from
	// destination space to source space. This is used for horizontal lines only, and is mainly
	// used to take advantage of memory coherence for horizontal spans.
	virtual void pointSpan(Span span) = 0;
	};

	class SkLinearBitmapPipeline::SampleProcessorInterface
	: public SkLinearBitmapPipeline::PointProcessorInterface {
	public:
	// Used for nearest neighbor when scale factor is 1.0. The span can just be repeated with no
	// edge pixel alignment problems. This is for handling a very common case.
	virtual void repeatSpan(Span span, int32_t repeatCount) = 0;
	};

	class SkLinearBitmapPipeline::DestinationInterface {
	public:
	virtual ~DestinationInterface() { }
	// Count is normally not needed, but in these early stages of development it is useful to
	// check bounds.
	// TODO(herb): 4/6/2016 - remove count when code is stable.
	virtual void setDestination(void* dst, int count) = 0;
	};

	class SkLinearBitmapPipeline::BlendProcessorInterface
	: public SkLinearBitmapPipeline::DestinationInterface {
	public:
	virtual void SK_VECTORCALL blendPixel(Sk4f pixel0) = 0;
	virtual void SK_VECTORCALL blend4Pixels(Sk4f p0, Sk4f p1, Sk4f p2, Sk4f p3) = 0;
	};

	class SkLinearBitmapPipeline::PixelAccessorInterface {
	public:
	virtual ~PixelAccessorInterface() { }
	virtual void SK_VECTORCALL getFewPixels(
	int n, Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2) const = 0;

	virtual void SK_VECTORCALL get4Pixels(
	Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const = 0;

	virtual void get4Pixels(
	const void* src, int index, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const = 0;

	virtual Sk4f getPixelFromRow(const void* row, int index) const = 0;

	virtual Sk4f getPixelAt(int index) const = 0;

	virtual const void* row(int y) const = 0;
	};

	#endif // SkLinearBitmapPipeline_core_DEFINED