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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include <string.h>
      6 #include <time.h>
      7 #include <algorithm>
      8 #include <numeric>
      9 #include <vector>
     10 
     11 #include "base/basictypes.h"
     12 #include "base/logging.h"
     13 #include "base/time/time.h"
     14 #include "skia/ext/convolver.h"
     15 #include "testing/gtest/include/gtest/gtest.h"
     16 #include "third_party/skia/include/core/SkBitmap.h"
     17 #include "third_party/skia/include/core/SkColorPriv.h"
     18 #include "third_party/skia/include/core/SkRect.h"
     19 #include "third_party/skia/include/core/SkTypes.h"
     20 
     21 namespace skia {
     22 
     23 namespace {
     24 
     25 // Fills the given filter with impulse functions for the range 0->num_entries.
     26 void FillImpulseFilter(int num_entries, ConvolutionFilter1D* filter) {
     27   float one = 1.0f;
     28   for (int i = 0; i < num_entries; i++)
     29     filter->AddFilter(i, &one, 1);
     30 }
     31 
     32 // Filters the given input with the impulse function, and verifies that it
     33 // does not change.
     34 void TestImpulseConvolution(const unsigned char* data, int width, int height) {
     35   int byte_count = width * height * 4;
     36 
     37   ConvolutionFilter1D filter_x;
     38   FillImpulseFilter(width, &filter_x);
     39 
     40   ConvolutionFilter1D filter_y;
     41   FillImpulseFilter(height, &filter_y);
     42 
     43   std::vector<unsigned char> output;
     44   output.resize(byte_count);
     45   BGRAConvolve2D(data, width * 4, true, filter_x, filter_y,
     46                  filter_x.num_values() * 4, &output[0], false);
     47 
     48   // Output should exactly match input.
     49   EXPECT_EQ(0, memcmp(data, &output[0], byte_count));
     50 }
     51 
     52 // Fills the destination filter with a box filter averaging every two pixels
     53 // to produce the output.
     54 void FillBoxFilter(int size, ConvolutionFilter1D* filter) {
     55   const float box[2] = { 0.5, 0.5 };
     56   for (int i = 0; i < size; i++)
     57     filter->AddFilter(i * 2, box, 2);
     58 }
     59 
     60 }  // namespace
     61 
     62 // Tests that each pixel, when set and run through the impulse filter, does
     63 // not change.
     64 TEST(Convolver, Impulse) {
     65   // We pick an "odd" size that is not likely to fit on any boundaries so that
     66   // we can see if all the widths and paddings are handled properly.
     67   int width = 15;
     68   int height = 31;
     69   int byte_count = width * height * 4;
     70   std::vector<unsigned char> input;
     71   input.resize(byte_count);
     72 
     73   unsigned char* input_ptr = &input[0];
     74   for (int y = 0; y < height; y++) {
     75     for (int x = 0; x < width; x++) {
     76       for (int channel = 0; channel < 3; channel++) {
     77         memset(input_ptr, 0, byte_count);
     78         input_ptr[(y * width + x) * 4 + channel] = 0xff;
     79         // Always set the alpha channel or it will attempt to "fix" it for us.
     80         input_ptr[(y * width + x) * 4 + 3] = 0xff;
     81         TestImpulseConvolution(input_ptr, width, height);
     82       }
     83     }
     84   }
     85 }
     86 
     87 // Tests that using a box filter to halve an image results in every square of 4
     88 // pixels in the original get averaged to a pixel in the output.
     89 TEST(Convolver, Halve) {
     90   static const int kSize = 16;
     91 
     92   int src_width = kSize;
     93   int src_height = kSize;
     94   int src_row_stride = src_width * 4;
     95   int src_byte_count = src_row_stride * src_height;
     96   std::vector<unsigned char> input;
     97   input.resize(src_byte_count);
     98 
     99   int dest_width = src_width / 2;
    100   int dest_height = src_height / 2;
    101   int dest_byte_count = dest_width * dest_height * 4;
    102   std::vector<unsigned char> output;
    103   output.resize(dest_byte_count);
    104 
    105   // First fill the array with a bunch of random data.
    106   srand(static_cast<unsigned>(time(NULL)));
    107   for (int i = 0; i < src_byte_count; i++)
    108     input[i] = rand() * 255 / RAND_MAX;
    109 
    110   // Compute the filters.
    111   ConvolutionFilter1D filter_x, filter_y;
    112   FillBoxFilter(dest_width, &filter_x);
    113   FillBoxFilter(dest_height, &filter_y);
    114 
    115   // Do the convolution.
    116   BGRAConvolve2D(&input[0], src_width, true, filter_x, filter_y,
    117                  filter_x.num_values() * 4, &output[0], false);
    118 
    119   // Compute the expected results and check, allowing for a small difference
    120   // to account for rounding errors.
    121   for (int y = 0; y < dest_height; y++) {
    122     for (int x = 0; x < dest_width; x++) {
    123       for (int channel = 0; channel < 4; channel++) {
    124         int src_offset = (y * 2 * src_row_stride + x * 2 * 4) + channel;
    125         int value = input[src_offset] +  // Top left source pixel.
    126                     input[src_offset + 4] +  // Top right source pixel.
    127                     input[src_offset + src_row_stride] +  // Lower left.
    128                     input[src_offset + src_row_stride + 4];  // Lower right.
    129         value /= 4;  // Average.
    130         int difference = value - output[(y * dest_width + x) * 4 + channel];
    131         EXPECT_TRUE(difference >= -1 || difference <= 1);
    132       }
    133     }
    134   }
    135 }
    136 
    137 // Tests the optimization in Convolver1D::AddFilter that avoids storing
    138 // leading/trailing zeroes.
    139 TEST(Convolver, AddFilter) {
    140   skia::ConvolutionFilter1D filter;
    141 
    142   const skia::ConvolutionFilter1D::Fixed* values = NULL;
    143   int filter_offset = 0;
    144   int filter_length = 0;
    145 
    146   // An all-zero filter is handled correctly, all factors ignored
    147   static const float factors1[] = { 0.0f, 0.0f, 0.0f };
    148   filter.AddFilter(11, factors1, arraysize(factors1));
    149   ASSERT_EQ(0, filter.max_filter());
    150   ASSERT_EQ(1, filter.num_values());
    151 
    152   values = filter.FilterForValue(0, &filter_offset, &filter_length);
    153   ASSERT_TRUE(values == NULL);   // No values => NULL.
    154   ASSERT_EQ(11, filter_offset);  // Same as input offset.
    155   ASSERT_EQ(0, filter_length);   // But no factors since all are zeroes.
    156 
    157   // Zeroes on the left are ignored
    158   static const float factors2[] = { 0.0f, 1.0f, 1.0f, 1.0f, 1.0f };
    159   filter.AddFilter(22, factors2, arraysize(factors2));
    160   ASSERT_EQ(4, filter.max_filter());
    161   ASSERT_EQ(2, filter.num_values());
    162 
    163   values = filter.FilterForValue(1, &filter_offset, &filter_length);
    164   ASSERT_TRUE(values != NULL);
    165   ASSERT_EQ(23, filter_offset);  // 22 plus 1 leading zero
    166   ASSERT_EQ(4, filter_length);   // 5 - 1 leading zero
    167 
    168   // Zeroes on the right are ignored
    169   static const float factors3[] = { 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f };
    170   filter.AddFilter(33, factors3, arraysize(factors3));
    171   ASSERT_EQ(5, filter.max_filter());
    172   ASSERT_EQ(3, filter.num_values());
    173 
    174   values = filter.FilterForValue(2, &filter_offset, &filter_length);
    175   ASSERT_TRUE(values != NULL);
    176   ASSERT_EQ(33, filter_offset);  // 33, same as input due to no leading zero
    177   ASSERT_EQ(5, filter_length);   // 7 - 2 trailing zeroes
    178 
    179   // Zeroes in leading & trailing positions
    180   static const float factors4[] = { 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f };
    181   filter.AddFilter(44, factors4, arraysize(factors4));
    182   ASSERT_EQ(5, filter.max_filter());  // No change from existing value.
    183   ASSERT_EQ(4, filter.num_values());
    184 
    185   values = filter.FilterForValue(3, &filter_offset, &filter_length);
    186   ASSERT_TRUE(values != NULL);
    187   ASSERT_EQ(46, filter_offset);  // 44 plus 2 leading zeroes
    188   ASSERT_EQ(3, filter_length);   // 7 - (2 leading + 2 trailing) zeroes
    189 
    190   // Zeroes surrounded by non-zero values are ignored
    191   static const float factors5[] = { 0.0f, 0.0f,
    192                                     1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f,
    193                                     0.0f };
    194   filter.AddFilter(55, factors5, arraysize(factors5));
    195   ASSERT_EQ(6, filter.max_filter());
    196   ASSERT_EQ(5, filter.num_values());
    197 
    198   values = filter.FilterForValue(4, &filter_offset, &filter_length);
    199   ASSERT_TRUE(values != NULL);
    200   ASSERT_EQ(57, filter_offset);  // 55 plus 2 leading zeroes
    201   ASSERT_EQ(6, filter_length);   // 9 - (2 leading + 1 trailing) zeroes
    202 
    203   // All-zero filters after the first one also work
    204   static const float factors6[] = { 0.0f };
    205   filter.AddFilter(66, factors6, arraysize(factors6));
    206   ASSERT_EQ(6, filter.max_filter());
    207   ASSERT_EQ(6, filter.num_values());
    208 
    209   values = filter.FilterForValue(5, &filter_offset, &filter_length);
    210   ASSERT_TRUE(values == NULL);   // filter_length == 0 => values is NULL
    211   ASSERT_EQ(66, filter_offset);  // value passed in
    212   ASSERT_EQ(0, filter_length);
    213 }
    214 
    215 void VerifySIMD(unsigned int source_width,
    216                 unsigned int source_height,
    217                 unsigned int dest_width,
    218                 unsigned int dest_height) {
    219   float filter[] = { 0.05f, -0.15f, 0.6f, 0.6f, -0.15f, 0.05f };
    220   // Preparing convolve coefficients.
    221   ConvolutionFilter1D x_filter, y_filter;
    222   for (unsigned int p = 0; p < dest_width; ++p) {
    223     unsigned int offset = source_width * p / dest_width;
    224     EXPECT_LT(offset, source_width);
    225     x_filter.AddFilter(offset, filter,
    226                        std::min<int>(arraysize(filter),
    227                                      source_width - offset));
    228   }
    229   x_filter.PaddingForSIMD();
    230   for (unsigned int p = 0; p < dest_height; ++p) {
    231     unsigned int offset = source_height * p / dest_height;
    232     y_filter.AddFilter(offset, filter,
    233                        std::min<int>(arraysize(filter),
    234                                      source_height - offset));
    235   }
    236   y_filter.PaddingForSIMD();
    237 
    238   // Allocate input and output skia bitmap.
    239   SkBitmap source, result_c, result_sse;
    240   source.allocN32Pixels(source_width, source_height);
    241   result_c.allocN32Pixels(dest_width, dest_height);
    242   result_sse.allocN32Pixels(dest_width, dest_height);
    243 
    244   // Randomize source bitmap for testing.
    245   unsigned char* src_ptr = static_cast<unsigned char*>(source.getPixels());
    246   for (int y = 0; y < source.height(); y++) {
    247     for (unsigned int x = 0; x < source.rowBytes(); x++)
    248       src_ptr[x] = rand() % 255;
    249     src_ptr += source.rowBytes();
    250   }
    251 
    252   // Test both cases with different has_alpha.
    253   for (int alpha = 0; alpha < 2; alpha++) {
    254     // Convolve using C code.
    255     base::TimeTicks resize_start;
    256     base::TimeDelta delta_c, delta_sse;
    257     unsigned char* r1 = static_cast<unsigned char*>(result_c.getPixels());
    258     unsigned char* r2 = static_cast<unsigned char*>(result_sse.getPixels());
    259 
    260     resize_start = base::TimeTicks::Now();
    261     BGRAConvolve2D(static_cast<const uint8*>(source.getPixels()),
    262                    static_cast<int>(source.rowBytes()),
    263                    (alpha != 0), x_filter, y_filter,
    264                    static_cast<int>(result_c.rowBytes()), r1, false);
    265     delta_c = base::TimeTicks::Now() - resize_start;
    266 
    267     resize_start = base::TimeTicks::Now();
    268     // Convolve using SSE2 code
    269     BGRAConvolve2D(static_cast<const uint8*>(source.getPixels()),
    270                    static_cast<int>(source.rowBytes()),
    271                    (alpha != 0), x_filter, y_filter,
    272                    static_cast<int>(result_sse.rowBytes()), r2, true);
    273     delta_sse = base::TimeTicks::Now() - resize_start;
    274 
    275     // Unfortunately I could not enable the performance check now.
    276     // Most bots use debug version, and there are great difference between
    277     // the code generation for intrinsic, etc. In release version speed
    278     // difference was 150%-200% depend on alpha channel presence;
    279     // while in debug version speed difference was 96%-120%.
    280     // TODO(jiesun): optimize further until we could enable this for
    281     // debug version too.
    282     // EXPECT_LE(delta_sse, delta_c);
    283 
    284     int64 c_us = delta_c.InMicroseconds();
    285     int64 sse_us = delta_sse.InMicroseconds();
    286     VLOG(1) << "from:" << source_width << "x" << source_height
    287             << " to:" << dest_width << "x" << dest_height
    288             << (alpha ? " with alpha" : " w/o alpha");
    289     VLOG(1) << "c:" << c_us << " sse:" << sse_us;
    290     VLOG(1) << "ratio:" << static_cast<float>(c_us) / sse_us;
    291 
    292     // Comparing result.
    293     for (unsigned int i = 0; i < dest_height; i++) {
    294       EXPECT_FALSE(memcmp(r1, r2, dest_width * 4)); // RGBA always
    295       r1 += result_c.rowBytes();
    296       r2 += result_sse.rowBytes();
    297     }
    298   }
    299 }
    300 
    301 TEST(Convolver, VerifySIMDEdgeCases) {
    302   srand(static_cast<unsigned int>(time(0)));
    303   // Loop over all possible (small) image sizes
    304   for (unsigned int width = 1; width < 20; width++) {
    305     for (unsigned int height = 1; height < 20; height++) {
    306       VerifySIMD(width, height, 8, 8);
    307       VerifySIMD(8, 8, width, height);
    308     }
    309   }
    310 }
    311 
    312 // Verify that lage upscales/downscales produce the same result
    313 // with and without SIMD.
    314 TEST(Convolver, VerifySIMDPrecision) {
    315   int source_sizes[][2] = { {1920, 1080}, {1377, 523}, {325, 241} };
    316   int dest_sizes[][2] = { {1280, 1024}, {177, 123} };
    317 
    318   srand(static_cast<unsigned int>(time(0)));
    319 
    320   // Loop over some specific source and destination dimensions.
    321   for (unsigned int i = 0; i < arraysize(source_sizes); ++i) {
    322     unsigned int source_width = source_sizes[i][0];
    323     unsigned int source_height = source_sizes[i][1];
    324     for (unsigned int j = 0; j < arraysize(dest_sizes); ++j) {
    325       unsigned int dest_width = dest_sizes[j][0];
    326       unsigned int dest_height = dest_sizes[j][1];
    327       VerifySIMD(source_width, source_height, dest_width, dest_height);
    328     }
    329   }
    330 }
    331 
    332 TEST(Convolver, SeparableSingleConvolution) {
    333   static const int kImgWidth = 1024;
    334   static const int kImgHeight = 1024;
    335   static const int kChannelCount = 3;
    336   static const int kStrideSlack = 22;
    337   ConvolutionFilter1D filter;
    338   const float box[5] = { 0.2f, 0.2f, 0.2f, 0.2f, 0.2f };
    339   filter.AddFilter(0, box, 5);
    340 
    341   // Allocate a source image and set to 0.
    342   const int src_row_stride = kImgWidth * kChannelCount + kStrideSlack;
    343   int src_byte_count = src_row_stride * kImgHeight;
    344   std::vector<unsigned char> input;
    345   const int signal_x = kImgWidth / 2;
    346   const int signal_y = kImgHeight / 2;
    347   input.resize(src_byte_count, 0);
    348   // The image has a single impulse pixel in channel 1, smack in the middle.
    349   const int non_zero_pixel_index =
    350       signal_y * src_row_stride + signal_x * kChannelCount + 1;
    351   input[non_zero_pixel_index] = 255;
    352 
    353   // Destination will be a single channel image with stide matching width.
    354   const int dest_row_stride = kImgWidth;
    355   const int dest_byte_count = dest_row_stride * kImgHeight;
    356   std::vector<unsigned char> output;
    357   output.resize(dest_byte_count);
    358 
    359   // Apply convolution in X.
    360   SingleChannelConvolveX1D(&input[0], src_row_stride, 1, kChannelCount,
    361                            filter, SkISize::Make(kImgWidth, kImgHeight),
    362                            &output[0], dest_row_stride, 0, 1, false);
    363   for (int x = signal_x - 2; x <= signal_x + 2; ++x)
    364     EXPECT_GT(output[signal_y * dest_row_stride + x], 0);
    365 
    366   EXPECT_EQ(output[signal_y * dest_row_stride + signal_x - 3], 0);
    367   EXPECT_EQ(output[signal_y * dest_row_stride + signal_x + 3], 0);
    368 
    369   // Apply convolution in Y.
    370   SingleChannelConvolveY1D(&input[0], src_row_stride, 1, kChannelCount,
    371                            filter, SkISize::Make(kImgWidth, kImgHeight),
    372                            &output[0], dest_row_stride, 0, 1, false);
    373   for (int y = signal_y - 2; y <= signal_y + 2; ++y)
    374     EXPECT_GT(output[y * dest_row_stride + signal_x], 0);
    375 
    376   EXPECT_EQ(output[(signal_y - 3) * dest_row_stride + signal_x], 0);
    377   EXPECT_EQ(output[(signal_y + 3) * dest_row_stride + signal_x], 0);
    378 
    379   EXPECT_EQ(output[signal_y * dest_row_stride + signal_x - 1], 0);
    380   EXPECT_EQ(output[signal_y * dest_row_stride + signal_x + 1], 0);
    381 
    382   // The main point of calling this is to invoke the routine on input without
    383   // padding.
    384   std::vector<unsigned char> output2;
    385   output2.resize(dest_byte_count);
    386   SingleChannelConvolveX1D(&output[0], dest_row_stride, 0, 1,
    387                            filter, SkISize::Make(kImgWidth, kImgHeight),
    388                            &output2[0], dest_row_stride, 0, 1, false);
    389   // This should be a result of 2D convolution.
    390   for (int x = signal_x - 2; x <= signal_x + 2; ++x) {
    391     for (int y = signal_y - 2; y <= signal_y + 2; ++y)
    392       EXPECT_GT(output2[y * dest_row_stride + x], 0);
    393   }
    394   EXPECT_EQ(output2[0], 0);
    395   EXPECT_EQ(output2[dest_row_stride - 1], 0);
    396   EXPECT_EQ(output2[dest_byte_count - 1], 0);
    397 }
    398 
    399 TEST(Convolver, SeparableSingleConvolutionEdges) {
    400   // The purpose of this test is to check if the implementation treats correctly
    401   // edges of the image.
    402   static const int kImgWidth = 600;
    403   static const int kImgHeight = 800;
    404   static const int kChannelCount = 3;
    405   static const int kStrideSlack = 22;
    406   static const int kChannel = 1;
    407   ConvolutionFilter1D filter;
    408   const float box[5] = { 0.2f, 0.2f, 0.2f, 0.2f, 0.2f };
    409   filter.AddFilter(0, box, 5);
    410 
    411   // Allocate a source image and set to 0.
    412   int src_row_stride = kImgWidth * kChannelCount + kStrideSlack;
    413   int src_byte_count = src_row_stride * kImgHeight;
    414   std::vector<unsigned char> input(src_byte_count);
    415 
    416   // Draw a frame around the image.
    417   for (int i = 0; i < src_byte_count; ++i) {
    418     int row = i / src_row_stride;
    419     int col = i % src_row_stride / kChannelCount;
    420     int channel = i % src_row_stride % kChannelCount;
    421     if (channel != kChannel || col > kImgWidth) {
    422       input[i] = 255;
    423     } else if (row == 0 || col == 0 ||
    424                col == kImgWidth - 1 || row == kImgHeight - 1) {
    425       input[i] = 100;
    426     } else if (row == 1 || col == 1 ||
    427                col == kImgWidth - 2 || row == kImgHeight - 2) {
    428       input[i] = 200;
    429     } else {
    430       input[i] = 0;
    431     }
    432   }
    433 
    434   // Destination will be a single channel image with stide matching width.
    435   int dest_row_stride = kImgWidth;
    436   int dest_byte_count = dest_row_stride * kImgHeight;
    437   std::vector<unsigned char> output;
    438   output.resize(dest_byte_count);
    439 
    440   // Apply convolution in X.
    441   SingleChannelConvolveX1D(&input[0], src_row_stride, 1, kChannelCount,
    442                            filter, SkISize::Make(kImgWidth, kImgHeight),
    443                            &output[0], dest_row_stride, 0, 1, false);
    444 
    445   // Sadly, comparison is not as simple as retaining all values.
    446   int invalid_values = 0;
    447   const unsigned char first_value = output[0];
    448   EXPECT_NEAR(first_value, 100, 1);
    449   for (int i = 0; i < dest_row_stride; ++i) {
    450     if (output[i] != first_value)
    451       ++invalid_values;
    452   }
    453   EXPECT_EQ(0, invalid_values);
    454 
    455   int test_row = 22;
    456   EXPECT_NEAR(output[test_row * dest_row_stride], 100, 1);
    457   EXPECT_NEAR(output[test_row * dest_row_stride + 1], 80, 1);
    458   EXPECT_NEAR(output[test_row * dest_row_stride + 2], 60, 1);
    459   EXPECT_NEAR(output[test_row * dest_row_stride + 3], 40, 1);
    460   EXPECT_NEAR(output[(test_row + 1) * dest_row_stride - 1], 100, 1);
    461   EXPECT_NEAR(output[(test_row + 1) * dest_row_stride - 2], 80, 1);
    462   EXPECT_NEAR(output[(test_row + 1) * dest_row_stride - 3], 60, 1);
    463   EXPECT_NEAR(output[(test_row + 1) * dest_row_stride - 4], 40, 1);
    464 
    465   SingleChannelConvolveY1D(&input[0], src_row_stride, 1, kChannelCount,
    466                            filter, SkISize::Make(kImgWidth, kImgHeight),
    467                            &output[0], dest_row_stride, 0, 1, false);
    468 
    469   int test_column = 42;
    470   EXPECT_NEAR(output[test_column], 100, 1);
    471   EXPECT_NEAR(output[test_column + dest_row_stride], 80, 1);
    472   EXPECT_NEAR(output[test_column + dest_row_stride * 2], 60, 1);
    473   EXPECT_NEAR(output[test_column + dest_row_stride * 3], 40, 1);
    474 
    475   EXPECT_NEAR(output[test_column + dest_row_stride * (kImgHeight - 1)], 100, 1);
    476   EXPECT_NEAR(output[test_column + dest_row_stride * (kImgHeight - 2)], 80, 1);
    477   EXPECT_NEAR(output[test_column + dest_row_stride * (kImgHeight - 3)], 60, 1);
    478   EXPECT_NEAR(output[test_column + dest_row_stride * (kImgHeight - 4)], 40, 1);
    479 }
    480 
    481 TEST(Convolver, SetUpGaussianConvolutionFilter) {
    482   ConvolutionFilter1D smoothing_filter;
    483   ConvolutionFilter1D gradient_filter;
    484   SetUpGaussianConvolutionKernel(&smoothing_filter, 4.5f, false);
    485   SetUpGaussianConvolutionKernel(&gradient_filter, 3.0f, true);
    486 
    487   int specified_filter_length;
    488   int filter_offset;
    489   int filter_length;
    490 
    491   const ConvolutionFilter1D::Fixed* smoothing_kernel =
    492       smoothing_filter.GetSingleFilter(
    493           &specified_filter_length, &filter_offset, &filter_length);
    494   EXPECT_TRUE(smoothing_kernel);
    495   std::vector<float> fp_smoothing_kernel(filter_length);
    496   std::transform(smoothing_kernel,
    497                  smoothing_kernel + filter_length,
    498                  fp_smoothing_kernel.begin(),
    499                  ConvolutionFilter1D::FixedToFloat);
    500   // Should sum-up to 1 (nearly), and all values whould be in ]0, 1[.
    501   EXPECT_NEAR(std::accumulate(
    502       fp_smoothing_kernel.begin(), fp_smoothing_kernel.end(), 0.0f),
    503               1.0f, 0.01f);
    504   EXPECT_GT(*std::min_element(fp_smoothing_kernel.begin(),
    505                               fp_smoothing_kernel.end()), 0.0f);
    506   EXPECT_LT(*std::max_element(fp_smoothing_kernel.begin(),
    507                               fp_smoothing_kernel.end()), 1.0f);
    508 
    509   const ConvolutionFilter1D::Fixed* gradient_kernel =
    510       gradient_filter.GetSingleFilter(
    511           &specified_filter_length, &filter_offset, &filter_length);
    512   EXPECT_TRUE(gradient_kernel);
    513   std::vector<float> fp_gradient_kernel(filter_length);
    514   std::transform(gradient_kernel,
    515                  gradient_kernel + filter_length,
    516                  fp_gradient_kernel.begin(),
    517                  ConvolutionFilter1D::FixedToFloat);
    518   // Should sum-up to 0, and all values whould be in ]-1.5, 1.5[.
    519   EXPECT_NEAR(std::accumulate(
    520       fp_gradient_kernel.begin(), fp_gradient_kernel.end(), 0.0f),
    521               0.0f, 0.01f);
    522   EXPECT_GT(*std::min_element(fp_gradient_kernel.begin(),
    523                               fp_gradient_kernel.end()), -1.5f);
    524   EXPECT_LT(*std::min_element(fp_gradient_kernel.begin(),
    525                               fp_gradient_kernel.end()), 0.0f);
    526   EXPECT_LT(*std::max_element(fp_gradient_kernel.begin(),
    527                               fp_gradient_kernel.end()), 1.5f);
    528   EXPECT_GT(*std::max_element(fp_gradient_kernel.begin(),
    529                               fp_gradient_kernel.end()), 0.0f);
    530 }
    531 
    532 }  // namespace skia
    533