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/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <math.h>
#include "Blur.h"
#include "MathUtils.h"
namespace android {
namespace uirenderer {
// This constant approximates the scaling done in the software path's
// "high quality" mode, in SkBlurMask::Blur() (1 / sqrt(3)).
static const float BLUR_SIGMA_SCALE = 0.57735f;
float Blur::convertRadiusToSigma(float radius) {
return radius > 0 ? BLUR_SIGMA_SCALE * radius + 0.5f : 0.0f;
}
float Blur::convertSigmaToRadius(float sigma) {
return sigma > 0.5f ? (sigma - 0.5f) / BLUR_SIGMA_SCALE : 0.0f;
}
// if the original radius was on an integer boundary and the resulting radius
// is within the conversion error tolerance then we attempt to snap to the
// original integer boundary.
uint32_t Blur::convertRadiusToInt(float radius) {
const float radiusCeil = ceilf(radius);
if (MathUtils::areEqual(radiusCeil, radius)) {
return radiusCeil;
}
return radius;
}
/**
* HWUI has used a slightly different equation than Skia to generate the value
* for sigma and to preserve compatibility we have kept that logic.
*
* Based on some experimental radius and sigma values we approximate the
* equation sigma = f(radius) as sigma = radius * 0.3 + 0.6. The larger the
* radius gets, the more our gaussian blur will resemble a box blur since with
* large sigma the gaussian curve begins to lose its shape.
*/
static float legacyConvertRadiusToSigma(float radius) {
return radius > 0 ? 0.3f * radius + 0.6f : 0.0f;
}
void Blur::generateGaussianWeights(float* weights, float radius) {
int32_t intRadius = convertRadiusToInt(radius);
// Compute gaussian weights for the blur
// e is the euler's number
static float e = 2.718281828459045f;
static float pi = 3.1415926535897932f;
// g(x) = ( 1 / sqrt( 2 * pi ) * sigma) * e ^ ( -x^2 / 2 * sigma^2 )
// x is of the form [-radius .. 0 .. radius]
// and sigma varies with radius.
float sigma = legacyConvertRadiusToSigma(radius);
// Now compute the coefficints
// We will store some redundant values to save some math during
// the blur calculations
// precompute some values
float coeff1 = 1.0f / (sqrt(2.0f * pi) * sigma);
float coeff2 = -1.0f / (2.0f * sigma * sigma);
float normalizeFactor = 0.0f;
for (int32_t r = -intRadius; r <= intRadius; r++) {
float floatR = (float)r;
weights[r + intRadius] = coeff1 * pow(e, floatR * floatR * coeff2);
normalizeFactor += weights[r + intRadius];
}
// Now we need to normalize the weights because all our coefficients need to add up to one
normalizeFactor = 1.0f / normalizeFactor;
for (int32_t r = -intRadius; r <= intRadius; r++) {
weights[r + intRadius] *= normalizeFactor;
}
}
void Blur::horizontal(float* weights, int32_t radius, const uint8_t* source, uint8_t* dest,
int32_t width, int32_t height) {
float blurredPixel = 0.0f;
float currentPixel = 0.0f;
for (int32_t y = 0; y < height; y++) {
const uint8_t* input = source + y * width;
uint8_t* output = dest + y * width;
for (int32_t x = 0; x < width; x++) {
blurredPixel = 0.0f;
const float* gPtr = weights;
// Optimization for non-border pixels
if (x > radius && x < (width - radius)) {
const uint8_t* i = input + (x - radius);
for (int r = -radius; r <= radius; r++) {
currentPixel = (float)(*i);
blurredPixel += currentPixel * gPtr[0];
gPtr++;
i++;
}
} else {
for (int32_t r = -radius; r <= radius; r++) {
// Stepping left and right away from the pixel
int validW = x + r;
if (validW < 0) {
validW = 0;
}
if (validW > width - 1) {
validW = width - 1;
}
currentPixel = (float)input[validW];
blurredPixel += currentPixel * gPtr[0];
gPtr++;
}
}
*output = (uint8_t)blurredPixel;
output++;
}
}
}
void Blur::vertical(float* weights, int32_t radius, const uint8_t* source, uint8_t* dest,
int32_t width, int32_t height) {
float blurredPixel = 0.0f;
float currentPixel = 0.0f;
for (int32_t y = 0; y < height; y++) {
uint8_t* output = dest + y * width;
for (int32_t x = 0; x < width; x++) {
blurredPixel = 0.0f;
const float* gPtr = weights;
const uint8_t* input = source + x;
// Optimization for non-border pixels
if (y > radius && y < (height - radius)) {
const uint8_t* i = input + ((y - radius) * width);
for (int32_t r = -radius; r <= radius; r++) {
currentPixel = (float)(*i);
blurredPixel += currentPixel * gPtr[0];
gPtr++;
i += width;
}
} else {
for (int32_t r = -radius; r <= radius; r++) {
int validH = y + r;
// Clamp to zero and width
if (validH < 0) {
validH = 0;
}
if (validH > height - 1) {
validH = height - 1;
}
const uint8_t* i = input + validH * width;
currentPixel = (float)(*i);
blurredPixel += currentPixel * gPtr[0];
gPtr++;
}
}
*output = (uint8_t)blurredPixel;
output++;
}
}
}
} // namespace uirenderer
} // namespace android
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