src/core/SkBitmapScaler.cpp - skia - Git at Google

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include "SkBitmapScaler.h"
 #include "SkBitmapFilter.h"
 #include "SkConvolver.h"
 #include "SkImageInfo.h"
 #include "SkPixmap.h"
 #include "SkRect.h"
 #include "SkTArray.h"

 // SkResizeFilter ----------------------------------------------------------------

 // Encapsulates computation and storage of the filters required for one complete
 // resize operation.
 class SkResizeFilter {
 public:
     SkResizeFilter(SkBitmapScaler::ResizeMethod method,
                    int srcFullWidth, int srcFullHeight,
                    float destWidth, float destHeight,
                    const SkRect& destSubset);
     ~SkResizeFilter() { delete fBitmapFilter; }

     // Returns the filled filter values.
     const SkConvolutionFilter1D& xFilter() { return fXFilter; }
     const SkConvolutionFilter1D& yFilter() { return fYFilter; }

 private:

     SkBitmapFilter* fBitmapFilter;

     // Computes one set of filters either horizontally or vertically. The caller
     // will specify the "min" and "max" rather than the bottom/top and
     // right/bottom so that the same code can be re-used in each dimension.
     //
     // |srcDependLo| and |srcDependSize| gives the range for the source
     // depend rectangle (horizontally or vertically at the caller's discretion
     // -- see above for what this means).
     //
     // Likewise, the range of destination values to compute and the scale factor
     // for the transform is also specified.

     void computeFilters(int srcSize,
                         float destSubsetLo, float destSubsetSize,
                         float scale,
                         SkConvolutionFilter1D* output);

     SkConvolutionFilter1D fXFilter;
     SkConvolutionFilter1D fYFilter;
 };

 SkResizeFilter::SkResizeFilter(SkBitmapScaler::ResizeMethod method,
                                int srcFullWidth, int srcFullHeight,
                                float destWidth, float destHeight,
                                const SkRect& destSubset) {

     SkASSERT(method >= SkBitmapScaler::RESIZE_FirstMethod &&
              method <= SkBitmapScaler::RESIZE_LastMethod);

     fBitmapFilter = nullptr;
     switch(method) {
         case SkBitmapScaler::RESIZE_BOX:
             fBitmapFilter = new SkBoxFilter;
             break;
         case SkBitmapScaler::RESIZE_TRIANGLE:
             fBitmapFilter = new SkTriangleFilter;
             break;
         case SkBitmapScaler::RESIZE_MITCHELL:
             fBitmapFilter = new SkMitchellFilter;
             break;
         case SkBitmapScaler::RESIZE_HAMMING:
             fBitmapFilter = new SkHammingFilter;
             break;
         case SkBitmapScaler::RESIZE_LANCZOS3:
             fBitmapFilter = new SkLanczosFilter;
             break;
     }


     float scaleX = destWidth / srcFullWidth;
     float scaleY = destHeight / srcFullHeight;

     this->computeFilters(srcFullWidth, destSubset.fLeft, destSubset.width(),
                          scaleX, &fXFilter);
     if (srcFullWidth == srcFullHeight &&
         destSubset.fLeft == destSubset.fTop &&
         destSubset.width() == destSubset.height()&&
         scaleX == scaleY) {
         fYFilter = fXFilter;
     } else {
         this->computeFilters(srcFullHeight, destSubset.fTop, destSubset.height(),
                           scaleY, &fYFilter);
     }
 }

 // TODO(egouriou): Take advantage of periods in the convolution.
 // Practical resizing filters are periodic outside of the border area.
 // For Lanczos, a scaling by a (reduced) factor of p/q (q pixels in the
 // source become p pixels in the destination) will have a period of p.
 // A nice consequence is a period of 1 when downscaling by an integral
 // factor. Downscaling from typical display resolutions is also bound
 // to produce interesting periods as those are chosen to have multiple
 // small factors.
 // Small periods reduce computational load and improve cache usage if
 // the coefficients can be shared. For periods of 1 we can consider
 // loading the factors only once outside the borders.
 void SkResizeFilter::computeFilters(int srcSize,
                                     float destSubsetLo, float destSubsetSize,
                                     float scale,
                                     SkConvolutionFilter1D* output) {
     float destSubsetHi = destSubsetLo + destSubsetSize;  // [lo, hi)

     // When we're doing a magnification, the scale will be larger than one. This
     // means the destination pixels are much smaller than the source pixels, and
     // that the range covered by the filter won't necessarily cover any source
     // pixel boundaries. Therefore, we use these clamped values (max of 1) for
     // some computations.
     float clampedScale = SkTMin(1.0f, scale);

     // This is how many source pixels from the center we need to count
     // to support the filtering function.
     float srcSupport = fBitmapFilter->width() / clampedScale;

     float invScale = 1.0f / scale;

     SkSTArray<64, float, true> filterValuesArray;
     SkSTArray<64, SkConvolutionFilter1D::ConvolutionFixed, true> fixedFilterValuesArray;

     // Loop over all pixels in the output range. We will generate one set of
     // filter values for each one. Those values will tell us how to blend the
     // source pixels to compute the destination pixel.

     // This is the pixel in the source directly under the pixel in the dest.
     // Note that we base computations on the "center" of the pixels. To see
     // why, observe that the destination pixel at coordinates (0, 0) in a 5.0x
     // downscale should "cover" the pixels around the pixel with *its center*
     // at coordinates (2.5, 2.5) in the source, not those around (0, 0).
     // Hence we need to scale coordinates (0.5, 0.5), not (0, 0).
     destSubsetLo = SkScalarFloorToScalar(destSubsetLo);
     destSubsetHi = SkScalarCeilToScalar(destSubsetHi);
     float srcPixel = (destSubsetLo + 0.5f) * invScale;
     int destLimit = SkScalarTruncToInt(destSubsetHi - destSubsetLo);
     output->reserveAdditional(destLimit, SkScalarCeilToInt(destLimit * srcSupport * 2));
     for (int destI = 0; destI < destLimit; srcPixel += invScale, destI++) {
         // Compute the (inclusive) range of source pixels the filter covers.
         float srcBegin = SkTMax(0.f, SkScalarFloorToScalar(srcPixel - srcSupport));
         float srcEnd = SkTMin(srcSize - 1.f, SkScalarCeilToScalar(srcPixel + srcSupport));

         // Compute the unnormalized filter value at each location of the source
         // it covers.

         // Sum of the filter values for normalizing.
         // Distance from the center of the filter, this is the filter coordinate
         // in source space. We also need to consider the center of the pixel
         // when comparing distance against 'srcPixel'. In the 5x downscale
         // example used above the distance from the center of the filter to
         // the pixel with coordinates (2, 2) should be 0, because its center
         // is at (2.5, 2.5).
         float destFilterDist = (srcBegin + 0.5f - srcPixel) * clampedScale;
         int filterCount = SkScalarTruncToInt(srcEnd - srcBegin) + 1;
         if (filterCount <= 0) {
             // true when srcSize is equal to srcPixel - srcSupport; this may be a bug
             return;
         }
         filterValuesArray.reset(filterCount);
         float filterSum = fBitmapFilter->evaluate_n(destFilterDist, clampedScale, filterCount,
                                                 filterValuesArray.begin());

         // The filter must be normalized so that we don't affect the brightness of
         // the image. Convert to normalized fixed point.
         int fixedSum = 0;
         fixedFilterValuesArray.reset(filterCount);
         const float* filterValues = filterValuesArray.begin();
         SkConvolutionFilter1D::ConvolutionFixed* fixedFilterValues = fixedFilterValuesArray.begin();
         float invFilterSum = 1 / filterSum;
         for (int fixedI = 0; fixedI < filterCount; fixedI++) {
             int curFixed = SkConvolutionFilter1D::FloatToFixed(filterValues[fixedI] * invFilterSum);
             fixedSum += curFixed;
             fixedFilterValues[fixedI] = SkToS16(curFixed);
         }
         SkASSERT(fixedSum <= 0x7FFF);

         // The conversion to fixed point will leave some rounding errors, which
         // we add back in to avoid affecting the brightness of the image. We
         // arbitrarily add this to the center of the filter array (this won't always
         // be the center of the filter function since it could get clipped on the
         // edges, but it doesn't matter enough to worry about that case).
         int leftovers = SkConvolutionFilter1D::FloatToFixed(1) - fixedSum;
         fixedFilterValues[filterCount / 2] += leftovers;

         // Now it's ready to go.
         output->AddFilter(SkScalarFloorToInt(srcBegin), fixedFilterValues, filterCount);
     }
 }

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

 static bool valid_for_resize(const SkPixmap& source, int dstW, int dstH) {
     // TODO: Seems like we shouldn't care about the swizzle of source, just that it's 8888
     return source.addr() && source.colorType() == kN32_SkColorType &&
            source.width() >= 1 && source.height() >= 1 && dstW >= 1 && dstH >= 1;
 }

 bool SkBitmapScaler::Resize(const SkPixmap& result, const SkPixmap& source, ResizeMethod method) {
     if (!valid_for_resize(source, result.width(), result.height())) {
         return false;
     }
     if (!result.addr() || result.colorType() != source.colorType()) {
         return false;
     }

     SkRect destSubset = SkRect::MakeIWH(result.width(), result.height());

     SkResizeFilter filter(method, source.width(), source.height(),
                           result.width(), result.height(), destSubset);

     // Get a subset encompassing this touched area. We construct the
     // offsets and row strides such that it looks like a new bitmap, while
     // referring to the old data.
     const uint8_t* sourceSubset = reinterpret_cast<const uint8_t*>(source.addr());

     return BGRAConvolve2D(sourceSubset, static_cast<int>(source.rowBytes()),
                           !source.isOpaque(), filter.xFilter(), filter.yFilter(),
                           static_cast<int>(result.rowBytes()),
                           static_cast<unsigned char*>(result.writable_addr()));
 }

 bool SkBitmapScaler::Resize(SkBitmap* resultPtr, const SkPixmap& source, ResizeMethod method,
                             int destWidth, int destHeight, SkBitmap::Allocator* allocator) {
     // Preflight some of the checks, to avoid allocating the result if we don't need it.
     if (!valid_for_resize(source, destWidth, destHeight)) {
         return false;
     }

     SkBitmap result;
     // Note: pass along the profile information even thought this is no the right answer because
     // this could be scaling in sRGB.
     result.setInfo(SkImageInfo::MakeN32(destWidth, destHeight, source.alphaType(),
                                         sk_ref_sp(source.info().colorSpace())));
     result.allocPixels(allocator);

     SkPixmap resultPM;
     if (!result.peekPixels(&resultPM) || !Resize(resultPM, source, method)) {
         return false;
     }

     *resultPtr = result;
     SkASSERT(resultPtr->getPixels());
     return true;
 }
	/*
	* Copyright 2015 Google Inc.
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#include "SkBitmapScaler.h"
	#include "SkBitmapFilter.h"
	#include "SkConvolver.h"
	#include "SkImageInfo.h"
	#include "SkPixmap.h"
	#include "SkRect.h"
	#include "SkTArray.h"

	// SkResizeFilter ----------------------------------------------------------------

	// Encapsulates computation and storage of the filters required for one complete
	// resize operation.
	class SkResizeFilter {
	public:
	SkResizeFilter(SkBitmapScaler::ResizeMethod method,
	int srcFullWidth, int srcFullHeight,
	float destWidth, float destHeight,
	const SkRect& destSubset);
	~SkResizeFilter() { delete fBitmapFilter; }

	// Returns the filled filter values.
	const SkConvolutionFilter1D& xFilter() { return fXFilter; }
	const SkConvolutionFilter1D& yFilter() { return fYFilter; }

	private:

	SkBitmapFilter* fBitmapFilter;

	// Computes one set of filters either horizontally or vertically. The caller
	// will specify the "min" and "max" rather than the bottom/top and
	// right/bottom so that the same code can be re-used in each dimension.
	//
	// \|srcDependLo\| and \|srcDependSize\| gives the range for the source
	// depend rectangle (horizontally or vertically at the caller's discretion
	// -- see above for what this means).
	//
	// Likewise, the range of destination values to compute and the scale factor
	// for the transform is also specified.

	void computeFilters(int srcSize,
	float destSubsetLo, float destSubsetSize,
	float scale,
	SkConvolutionFilter1D* output);

	SkConvolutionFilter1D fXFilter;
	SkConvolutionFilter1D fYFilter;
	};

	SkResizeFilter::SkResizeFilter(SkBitmapScaler::ResizeMethod method,
	int srcFullWidth, int srcFullHeight,
	float destWidth, float destHeight,
	const SkRect& destSubset) {

	SkASSERT(method >= SkBitmapScaler::RESIZE_FirstMethod &&
	method <= SkBitmapScaler::RESIZE_LastMethod);

	fBitmapFilter = nullptr;
	switch(method) {
	case SkBitmapScaler::RESIZE_BOX:
	fBitmapFilter = new SkBoxFilter;
	break;
	case SkBitmapScaler::RESIZE_TRIANGLE:
	fBitmapFilter = new SkTriangleFilter;
	break;
	case SkBitmapScaler::RESIZE_MITCHELL:
	fBitmapFilter = new SkMitchellFilter;
	break;
	case SkBitmapScaler::RESIZE_HAMMING:
	fBitmapFilter = new SkHammingFilter;
	break;
	case SkBitmapScaler::RESIZE_LANCZOS3:
	fBitmapFilter = new SkLanczosFilter;
	break;
	}


	float scaleX = destWidth / srcFullWidth;
	float scaleY = destHeight / srcFullHeight;

	this->computeFilters(srcFullWidth, destSubset.fLeft, destSubset.width(),
	scaleX, &fXFilter);
	if (srcFullWidth == srcFullHeight &&
	destSubset.fLeft == destSubset.fTop &&
	destSubset.width() == destSubset.height()&&
	scaleX == scaleY) {
	fYFilter = fXFilter;
	} else {
	this->computeFilters(srcFullHeight, destSubset.fTop, destSubset.height(),
	scaleY, &fYFilter);
	}
	}

	// TODO(egouriou): Take advantage of periods in the convolution.
	// Practical resizing filters are periodic outside of the border area.
	// For Lanczos, a scaling by a (reduced) factor of p/q (q pixels in the
	// source become p pixels in the destination) will have a period of p.
	// A nice consequence is a period of 1 when downscaling by an integral
	// factor. Downscaling from typical display resolutions is also bound
	// to produce interesting periods as those are chosen to have multiple
	// small factors.
	// Small periods reduce computational load and improve cache usage if
	// the coefficients can be shared. For periods of 1 we can consider
	// loading the factors only once outside the borders.
	void SkResizeFilter::computeFilters(int srcSize,
	float destSubsetLo, float destSubsetSize,
	float scale,
	SkConvolutionFilter1D* output) {
	float destSubsetHi = destSubsetLo + destSubsetSize; // [lo, hi)

	// When we're doing a magnification, the scale will be larger than one. This
	// means the destination pixels are much smaller than the source pixels, and
	// that the range covered by the filter won't necessarily cover any source
	// pixel boundaries. Therefore, we use these clamped values (max of 1) for
	// some computations.
	float clampedScale = SkTMin(1.0f, scale);

	// This is how many source pixels from the center we need to count
	// to support the filtering function.
	float srcSupport = fBitmapFilter->width() / clampedScale;

	float invScale = 1.0f / scale;

	SkSTArray<64, float, true> filterValuesArray;
	SkSTArray<64, SkConvolutionFilter1D::ConvolutionFixed, true> fixedFilterValuesArray;

	// Loop over all pixels in the output range. We will generate one set of
	// filter values for each one. Those values will tell us how to blend the
	// source pixels to compute the destination pixel.

	// This is the pixel in the source directly under the pixel in the dest.
	// Note that we base computations on the "center" of the pixels. To see
	// why, observe that the destination pixel at coordinates (0, 0) in a 5.0x
	// downscale should "cover" the pixels around the pixel with its center
	// at coordinates (2.5, 2.5) in the source, not those around (0, 0).
	// Hence we need to scale coordinates (0.5, 0.5), not (0, 0).
	destSubsetLo = SkScalarFloorToScalar(destSubsetLo);
	destSubsetHi = SkScalarCeilToScalar(destSubsetHi);
	float srcPixel = (destSubsetLo + 0.5f) * invScale;
	int destLimit = SkScalarTruncToInt(destSubsetHi - destSubsetLo);
	output->reserveAdditional(destLimit, SkScalarCeilToInt(destLimit * srcSupport * 2));
	for (int destI = 0; destI < destLimit; srcPixel += invScale, destI++) {
	// Compute the (inclusive) range of source pixels the filter covers.
	float srcBegin = SkTMax(0.f, SkScalarFloorToScalar(srcPixel - srcSupport));
	float srcEnd = SkTMin(srcSize - 1.f, SkScalarCeilToScalar(srcPixel + srcSupport));

	// Compute the unnormalized filter value at each location of the source
	// it covers.

	// Sum of the filter values for normalizing.
	// Distance from the center of the filter, this is the filter coordinate
	// in source space. We also need to consider the center of the pixel
	// when comparing distance against 'srcPixel'. In the 5x downscale
	// example used above the distance from the center of the filter to
	// the pixel with coordinates (2, 2) should be 0, because its center
	// is at (2.5, 2.5).
	float destFilterDist = (srcBegin + 0.5f - srcPixel) * clampedScale;
	int filterCount = SkScalarTruncToInt(srcEnd - srcBegin) + 1;
	if (filterCount <= 0) {
	// true when srcSize is equal to srcPixel - srcSupport; this may be a bug
	return;
	}
	filterValuesArray.reset(filterCount);
	float filterSum = fBitmapFilter->evaluate_n(destFilterDist, clampedScale, filterCount,
	filterValuesArray.begin());

	// The filter must be normalized so that we don't affect the brightness of
	// the image. Convert to normalized fixed point.
	int fixedSum = 0;
	fixedFilterValuesArray.reset(filterCount);
	const float* filterValues = filterValuesArray.begin();
	SkConvolutionFilter1D::ConvolutionFixed* fixedFilterValues = fixedFilterValuesArray.begin();
	float invFilterSum = 1 / filterSum;
	for (int fixedI = 0; fixedI < filterCount; fixedI++) {
	int curFixed = SkConvolutionFilter1D::FloatToFixed(filterValues[fixedI] * invFilterSum);
	fixedSum += curFixed;
	fixedFilterValues[fixedI] = SkToS16(curFixed);
	}
	SkASSERT(fixedSum <= 0x7FFF);

	// The conversion to fixed point will leave some rounding errors, which
	// we add back in to avoid affecting the brightness of the image. We
	// arbitrarily add this to the center of the filter array (this won't always
	// be the center of the filter function since it could get clipped on the
	// edges, but it doesn't matter enough to worry about that case).
	int leftovers = SkConvolutionFilter1D::FloatToFixed(1) - fixedSum;
	fixedFilterValues[filterCount / 2] += leftovers;

	// Now it's ready to go.
	output->AddFilter(SkScalarFloorToInt(srcBegin), fixedFilterValues, filterCount);
	}
	}

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

	static bool valid_for_resize(const SkPixmap& source, int dstW, int dstH) {
	// TODO: Seems like we shouldn't care about the swizzle of source, just that it's 8888
	return source.addr() && source.colorType() == kN32_SkColorType &&
	source.width() >= 1 && source.height() >= 1 && dstW >= 1 && dstH >= 1;
	}

	bool SkBitmapScaler::Resize(const SkPixmap& result, const SkPixmap& source, ResizeMethod method) {
	if (!valid_for_resize(source, result.width(), result.height())) {
	return false;
	}
	if (!result.addr() \|\| result.colorType() != source.colorType()) {
	return false;
	}

	SkRect destSubset = SkRect::MakeIWH(result.width(), result.height());

	SkResizeFilter filter(method, source.width(), source.height(),
	result.width(), result.height(), destSubset);

	// Get a subset encompassing this touched area. We construct the
	// offsets and row strides such that it looks like a new bitmap, while
	// referring to the old data.
	const uint8_t* sourceSubset = reinterpret_cast<const uint8_t*>(source.addr());

	return BGRAConvolve2D(sourceSubset, static_cast<int>(source.rowBytes()),
	!source.isOpaque(), filter.xFilter(), filter.yFilter(),
	static_cast<int>(result.rowBytes()),
	static_cast<unsigned char*>(result.writable_addr()));
	}

	bool SkBitmapScaler::Resize(SkBitmap* resultPtr, const SkPixmap& source, ResizeMethod method,
	int destWidth, int destHeight, SkBitmap::Allocator* allocator) {
	// Preflight some of the checks, to avoid allocating the result if we don't need it.
	if (!valid_for_resize(source, destWidth, destHeight)) {
	return false;
	}

	SkBitmap result;
	// Note: pass along the profile information even thought this is no the right answer because
	// this could be scaling in sRGB.
	result.setInfo(SkImageInfo::MakeN32(destWidth, destHeight, source.alphaType(),
	sk_ref_sp(source.info().colorSpace())));
	result.allocPixels(allocator);

	SkPixmap resultPM;
	if (!result.peekPixels(&resultPM) \|\| !Resize(resultPM, source, method)) {
	return false;
	}

	*resultPtr = result;
	SkASSERT(resultPtr->getPixels());
	return true;
	}