blob: 3501ac8a879f42a51c0e2e44f8efa8a31d4b2fb4 [file] [log] [blame]
#include "SkBitmapScaler.h"
#include "SkBitmapFilter.h"
#include "SkRect.h"
#include "SkTArray.h"
#include "SkErrorInternals.h"
#include "SkConvolver.h"
// SkResizeFilter ----------------------------------------------------------------
// Encapsulates computation and storage of the filters required for one complete
// resize operation.
class SkResizeFilter {
SkResizeFilter(SkBitmapScaler::ResizeMethod method,
int srcFullWidth, int srcFullHeight,
float destWidth, float destHeight,
const SkRect& destSubset,
const SkConvolutionProcs& convolveProcs);
~SkResizeFilter() {
SkDELETE( fBitmapFilter );
// Returns the filled filter values.
const SkConvolutionFilter1D& xFilter() { return fXFilter; }
const SkConvolutionFilter1D& yFilter() { return fYFilter; }
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,
const SkConvolutionProcs& convolveProcs);
SkConvolutionFilter1D fXFilter;
SkConvolutionFilter1D fYFilter;
SkResizeFilter::SkResizeFilter(SkBitmapScaler::ResizeMethod method,
int srcFullWidth, int srcFullHeight,
float destWidth, float destHeight,
const SkRect& destSubset,
const SkConvolutionProcs& convolveProcs) {
// method will only ever refer to an "algorithm method".
(method <= SkBitmapScaler::RESIZE_LAST_ALGORITHM_METHOD));
switch(method) {
case SkBitmapScaler::RESIZE_BOX:
fBitmapFilter = SkNEW(SkBoxFilter);
case SkBitmapScaler::RESIZE_TRIANGLE:
fBitmapFilter = SkNEW(SkTriangleFilter);
case SkBitmapScaler::RESIZE_MITCHELL:
fBitmapFilter = SkNEW_ARGS(SkMitchellFilter, (1.f/3.f, 1.f/3.f));
case SkBitmapScaler::RESIZE_HAMMING:
fBitmapFilter = SkNEW(SkHammingFilter);
case SkBitmapScaler::RESIZE_LANCZOS3:
fBitmapFilter = SkNEW(SkLanczosFilter);
fBitmapFilter = SkNEW_ARGS(SkMitchellFilter, (1.f/3.f, 1.f/3.f));
float scaleX = destWidth / srcFullWidth;
float scaleY = destHeight / srcFullHeight;
this->computeFilters(srcFullWidth, destSubset.fLeft, destSubset.width(),
scaleX, &fXFilter, convolveProcs);
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, convolveProcs);
// 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,
const SkConvolutionProcs& convolveProcs) {
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;
// Speed up the divisions below by turning them into multiplies.
float invScale = 1.0f / scale;
SkTArray<float> filterValues(64);
SkTArray<short> fixedFilterValues(64);
// 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.
for (int destSubsetI = SkScalarFloorToInt(destSubsetLo); destSubsetI < SkScalarCeilToInt(destSubsetHi);
destSubsetI++) {
// Reset the arrays. We don't declare them inside so they can re-use the
// same malloc-ed buffer.
// 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).
float srcPixel = (static_cast<float>(destSubsetI) + 0.5f) * invScale;
// Compute the (inclusive) range of source pixels the filter covers.
int srcBegin = SkTMax(0, SkScalarFloorToInt(srcPixel - srcSupport));
int srcEnd = SkTMin(srcSize - 1, SkScalarCeilToInt(srcPixel + srcSupport));
// Compute the unnormalized filter value at each location of the source
// it covers.
float filterSum = 0.0f; // Sub of the filter values for normalizing.
for (int curFilterPixel = srcBegin; curFilterPixel <= srcEnd;
curFilterPixel++) {
// 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 srcFilterDist =
((static_cast<float>(curFilterPixel) + 0.5f) - srcPixel);
// Since the filter really exists in dest space, map it there.
float destFilterDist = srcFilterDist * clampedScale;
// Compute the filter value at that location.
float filterValue = fBitmapFilter->evaluate(destFilterDist);
filterSum += filterValue;
// The filter must be normalized so that we don't affect the brightness of
// the image. Convert to normalized fixed point.
short fixedSum = 0;
for (int i = 0; i < filterValues.count(); i++) {
short curFixed = output->FloatToFixed(filterValues[i] / filterSum);
fixedSum += curFixed;
// 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).
short leftovers = output->FloatToFixed(1.0f) - fixedSum;
fixedFilterValues[fixedFilterValues.count() / 2] += leftovers;
// Now it's ready to go.
output->AddFilter(srcBegin, &fixedFilterValues[0],
if (convolveProcs.fApplySIMDPadding) {
convolveProcs.fApplySIMDPadding( output );
static SkBitmapScaler::ResizeMethod ResizeMethodToAlgorithmMethod(
SkBitmapScaler::ResizeMethod method) {
// Convert any "Quality Method" into an "Algorithm Method"
if (method >= SkBitmapScaler::RESIZE_FIRST_ALGORITHM_METHOD &&
method <= SkBitmapScaler::RESIZE_LAST_ALGORITHM_METHOD) {
return method;
// The call to SkBitmapScalerGtv::Resize() above took care of
// GPU-acceleration in the cases where it is possible. So now we just
// pick the appropriate software method for each resize quality.
switch (method) {
// Users of RESIZE_GOOD are willing to trade a lot of quality to
// get speed, allowing the use of linear resampling to get hardware
// acceleration (SRB). Hence any of our "good" software filters
// will be acceptable, so we use a triangle.
case SkBitmapScaler::RESIZE_GOOD:
return SkBitmapScaler::RESIZE_TRIANGLE;
// Users of RESIZE_BETTER are willing to trade some quality in order
// to improve performance, but are guaranteed not to devolve to a linear
// resampling. In visual tests we see that Hamming-1 is not as good as
// Lanczos-2, however it is about 40% faster and Lanczos-2 itself is
// about 30% faster than Lanczos-3. The use of Hamming-1 has been deemed
// an acceptable trade-off between quality and speed.
case SkBitmapScaler::RESIZE_BETTER:
return SkBitmapScaler::RESIZE_HAMMING;
return SkBitmapScaler::RESIZE_LANCZOS3;
return SkBitmapScaler::RESIZE_MITCHELL;
// static
bool SkBitmapScaler::Resize(SkBitmap* resultPtr,
const SkBitmap& source,
ResizeMethod method,
float destWidth, float destHeight,
SkBitmap::Allocator* allocator) {
SkConvolutionProcs convolveProcs= { 0, NULL, NULL, NULL, NULL };
SkRect destSubset = { 0, 0, destWidth, destHeight };
// Ensure that the ResizeMethod enumeration is sound.
SkRect dest = { 0, 0, destWidth, destHeight };
if (!dest.contains(destSubset)) {
SkErrorInternals::SetError( kInvalidArgument_SkError,
"Sorry, the destination bitmap scale subset "
"falls outside the full destination bitmap." );
return false;
// If the size of source or destination is 0, i.e. 0x0, 0xN or Nx0, just
// return empty.
if (source.width() < 1 || source.height() < 1 ||
destWidth < 1 || destHeight < 1) {
// todo: seems like we could handle negative dstWidth/Height, since that
// is just a negative scale (flip)
return false;
method = ResizeMethodToAlgorithmMethod(method);
// Check that we deal with an "algorithm methods" from this point onward.
(method <= SkBitmapScaler::RESIZE_LAST_ALGORITHM_METHOD));
SkAutoLockPixels locker(source);
if (!source.readyToDraw() ||
source.colorType() != kN32_SkColorType) {
return false;
SkResizeFilter filter(method, source.width(), source.height(),
destWidth, destHeight, destSubset, convolveProcs);
// Get a source bitmap 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 unsigned char* sourceSubset =
reinterpret_cast<const unsigned char*>(source.getPixels());
// Convolve into the result.
SkBitmap result;
result.allocPixels(allocator, NULL);
if (!result.readyToDraw()) {
return false;
BGRAConvolve2D(sourceSubset, static_cast<int>(source.rowBytes()),
!source.isOpaque(), filter.xFilter(), filter.yFilter(),
static_cast<unsigned char*>(result.getPixels()),
convolveProcs, true);
*resultPtr = result;
return true;
// static -- simpler interface to the resizer; returns a default bitmap if scaling
// fails for any reason. This is the interface that Chrome expects.
SkBitmap SkBitmapScaler::Resize(const SkBitmap& source,
ResizeMethod method,
float destWidth, float destHeight,
SkBitmap::Allocator* allocator) {
SkBitmap result;
if (!Resize(&result, source, method, destWidth, destHeight, allocator)) {
return SkBitmap();
return result;