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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include <math.h>
     18 
     19 #include "Blur.h"
     20 #include "MathUtils.h"
     21 
     22 namespace android {
     23 namespace uirenderer {
     24 
     25 // This constant approximates the scaling done in the software path's
     26 // "high quality" mode, in SkBlurMask::Blur() (1 / sqrt(3)).
     27 static const float BLUR_SIGMA_SCALE = 0.57735f;
     28 
     29 float Blur::convertRadiusToSigma(float radius) {
     30     return radius > 0 ? BLUR_SIGMA_SCALE * radius + 0.5f : 0.0f;
     31 }
     32 
     33 float Blur::convertSigmaToRadius(float sigma) {
     34     return sigma > 0.5f ? (sigma - 0.5f) / BLUR_SIGMA_SCALE : 0.0f;
     35 }
     36 
     37 // if the original radius was on an integer boundary and the resulting radius
     38 // is within the conversion error tolerance then we attempt to snap to the
     39 // original integer boundary.
     40 uint32_t Blur::convertRadiusToInt(float radius) {
     41     const float radiusCeil  = ceilf(radius);
     42     if (MathUtils::areEqual(radiusCeil, radius)) {
     43         return radiusCeil;
     44     }
     45     return radius;
     46 }
     47 
     48 /**
     49  * HWUI has used a slightly different equation than Skia to generate the value
     50  * for sigma and to preserve compatibility we have kept that logic.
     51  *
     52  * Based on some experimental radius and sigma values we approximate the
     53  * equation sigma = f(radius) as sigma = radius * 0.3  + 0.6.  The larger the
     54  * radius gets, the more our gaussian blur will resemble a box blur since with
     55  * large sigma the gaussian curve begins to lose its shape.
     56  */
     57 static float legacyConvertRadiusToSigma(float radius) {
     58     return radius > 0 ? 0.3f * radius + 0.6f : 0.0f;
     59 }
     60 
     61 void Blur::generateGaussianWeights(float* weights, float radius) {
     62     int32_t intRadius = convertRadiusToInt(radius);
     63 
     64     // Compute gaussian weights for the blur
     65     // e is the euler's number
     66     static float e = 2.718281828459045f;
     67     static float pi = 3.1415926535897932f;
     68     // g(x) = ( 1 / sqrt( 2 * pi ) * sigma) * e ^ ( -x^2 / 2 * sigma^2 )
     69     // x is of the form [-radius .. 0 .. radius]
     70     // and sigma varies with radius.
     71     float sigma = legacyConvertRadiusToSigma(radius);
     72 
     73     // Now compute the coefficints
     74     // We will store some redundant values to save some math during
     75     // the blur calculations
     76     // precompute some values
     77     float coeff1 = 1.0f / (sqrt(2.0f * pi) * sigma);
     78     float coeff2 = - 1.0f / (2.0f * sigma * sigma);
     79 
     80     float normalizeFactor = 0.0f;
     81     for (int32_t r = -intRadius; r <= intRadius; r ++) {
     82         float floatR = (float) r;
     83         weights[r + intRadius] = coeff1 * pow(e, floatR * floatR * coeff2);
     84         normalizeFactor += weights[r + intRadius];
     85     }
     86 
     87     //Now we need to normalize the weights because all our coefficients need to add up to one
     88     normalizeFactor = 1.0f / normalizeFactor;
     89     for (int32_t r = -intRadius; r <= intRadius; r ++) {
     90         weights[r + intRadius] *= normalizeFactor;
     91     }
     92 }
     93 
     94 void Blur::horizontal(float* weights, int32_t radius,
     95         const uint8_t* source, uint8_t* dest, int32_t width, int32_t height) {
     96     float blurredPixel = 0.0f;
     97     float currentPixel = 0.0f;
     98 
     99     for (int32_t y = 0; y < height; y ++) {
    100 
    101         const uint8_t* input = source + y * width;
    102         uint8_t* output = dest + y * width;
    103 
    104         for (int32_t x = 0; x < width; x ++) {
    105             blurredPixel = 0.0f;
    106             const float* gPtr = weights;
    107             // Optimization for non-border pixels
    108             if (x > radius && x < (width - radius)) {
    109                 const uint8_t *i = input + (x - radius);
    110                 for (int r = -radius; r <= radius; r ++) {
    111                     currentPixel = (float) (*i);
    112                     blurredPixel += currentPixel * gPtr[0];
    113                     gPtr++;
    114                     i++;
    115                 }
    116             } else {
    117                 for (int32_t r = -radius; r <= radius; r ++) {
    118                     // Stepping left and right away from the pixel
    119                     int validW = x + r;
    120                     if (validW < 0) {
    121                         validW = 0;
    122                     }
    123                     if (validW > width - 1) {
    124                         validW = width - 1;
    125                     }
    126 
    127                     currentPixel = (float) input[validW];
    128                     blurredPixel += currentPixel * gPtr[0];
    129                     gPtr++;
    130                 }
    131             }
    132             *output = (uint8_t)blurredPixel;
    133             output ++;
    134         }
    135     }
    136 }
    137 
    138 void Blur::vertical(float* weights, int32_t radius,
    139         const uint8_t* source, uint8_t* dest, int32_t width, int32_t height) {
    140     float blurredPixel = 0.0f;
    141     float currentPixel = 0.0f;
    142 
    143     for (int32_t y = 0; y < height; y ++) {
    144         uint8_t* output = dest + y * width;
    145 
    146         for (int32_t x = 0; x < width; x ++) {
    147             blurredPixel = 0.0f;
    148             const float* gPtr = weights;
    149             const uint8_t* input = source + x;
    150             // Optimization for non-border pixels
    151             if (y > radius && y < (height - radius)) {
    152                 const uint8_t *i = input + ((y - radius) * width);
    153                 for (int32_t r = -radius; r <= radius; r ++) {
    154                     currentPixel = (float) (*i);
    155                     blurredPixel += currentPixel * gPtr[0];
    156                     gPtr++;
    157                     i += width;
    158                 }
    159             } else {
    160                 for (int32_t r = -radius; r <= radius; r ++) {
    161                     int validH = y + r;
    162                     // Clamp to zero and width
    163                     if (validH < 0) {
    164                         validH = 0;
    165                     }
    166                     if (validH > height - 1) {
    167                         validH = height - 1;
    168                     }
    169 
    170                     const uint8_t *i = input + validH * width;
    171                     currentPixel = (float) (*i);
    172                     blurredPixel += currentPixel * gPtr[0];
    173                     gPtr++;
    174                 }
    175             }
    176             *output = (uint8_t) blurredPixel;
    177             output++;
    178         }
    179     }
    180 }
    181 
    182 }; // namespace uirenderer
    183 }; // namespace android
    184