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Prefer native scaling to sampling

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In the cases we have come across so far, native scaling has better performance
and correctness than sampling.  If native scaling is supported we want to use
it.

Jpegs native scale rounds up.
Ex: An 11x11 image with sampleSize=8 scales to 2x2.

SkScaledCodec rounds down.
Ex: An 11x11 image with sampleSize=8 scales to 1x1.

Before the CL, we would choose to use SkScaledCodec because it scales closer to
the "ideal" scale.

I think we want to go with the native option as long as its within 1 of the
ideal value.
BUG=skia:

Review URL: https://codereview.chromium.org/1284243004
This commit is contained in:
msarett 2015-08-18 08:03:58 -07:00 committed by Commit bot
parent 0628a52b0c
commit a83593b88a
1 changed files with 11 additions and 5 deletions
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16
src/codec/SkScaledCodec.cpp
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@ -53,7 +53,7 @@ static int get_scaled_dimension(int srcDimension, int sampleSize) {
return srcDimension / sampleSize;
}
static SkISize best_scaled_dimensions(const SkISize& origDims, const SkISize& nativeDims,
static SkISize best_scaled_dimensions(const SkISize& origDims, const SkISize& nativeDims,
const SkISize& scaledCodecDims, float desiredScale) {
if (nativeDims == scaledCodecDims) {
// does not matter which to return if equal. Return here to skip below calculations
@ -65,18 +65,24 @@ static SkISize best_scaled_dimensions(const SkISize& origDims, const SkISize& na
// calculate difference between native dimensions and ideal dimensions
float nativeWDiff = SkTAbs(idealWidth - nativeDims.width());
float nativeHDiff = SkTAbs(idealHeight - nativeDims.height());
float nativeDiff = (nativeWDiff + nativeHDiff) / 2;
float nativeDiff = nativeWDiff + nativeHDiff;
// Native scaling is preferred to sampling. If we can scale natively to
// within one of the ideal value, we should choose to scale natively.
if (nativeWDiff < 1.0f && nativeHDiff < 1.0f) {
return nativeDims;
}
// calculate difference between scaledCodec dimensions and ideal dimensions
float scaledCodecWDiff = SkTAbs(idealWidth - scaledCodecDims.width());
float scaledCodecHDiff = SkTAbs(idealHeight - scaledCodecDims.height());
float scaledCodecDiff = (scaledCodecWDiff + scaledCodecHDiff) / 2;
float scaledCodecDiff = scaledCodecWDiff + scaledCodecHDiff;
// return dimensions closest to ideal dimensions.
// If the differences are equal, return nativeDims, as native scaling is more efficient.
return nativeDiff > scaledCodecDiff ? scaledCodecDims : nativeDims;
}
}
/*
* Return a valid set of output dimensions for this decoder, given an input scale
*/
@ -98,7 +104,7 @@ SkISize SkScaledCodec::onGetScaledDimensions(float desiredScale) const {
// Return the calculated output dimensions for the given scale
scaledCodecDimensions = SkISize::Make(scaledWidth, scaledHeight);
return best_scaled_dimensions(this->getInfo().dimensions(), nativeDimensions,
return best_scaled_dimensions(this->getInfo().dimensions(), nativeDimensions,
scaledCodecDimensions, desiredScale);
}