Complete (but inefficient) implementation of the image retargetting method.

skia/ext/convolver.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKIA_EXT_CONVOLVER_H_
 #define SKIA_EXT_CONVOLVER_H_
 
 #include <cmath>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/cpu.h"
+#include "third_party/skia/include/core/SkSize.h"
 #include "third_party/skia/include/core/SkTypes.h"
 
 // We can build SSE2 optimized versions for all x86 CPUs
 // except when building for the IOS emulator.
 #if defined(ARCH_CPU_X86_FAMILY) && !defined(OS_IOS)
 #define SIMD_SSE2 1
 #define SIMD_PADDING 8  // 8 * int16
 #endif
 
 // avoid confusion with Mac OS X's math library (Carbon)
@@ skipping 69 matching lines @@
   // Retrieves a filter for the given |value_offset|, a position in the output
   // image in the direction we're convolving. The offset and length of the
   // filter values are put into the corresponding out arguments (see AddFilter
   // above for what these mean), and a pointer to the first scaling factor is
   // returned. There will be |filter_length| values in this array.
   inline const Fixed* FilterForValue(int value_offset,
                                      int* filter_offset,
                                      int* filter_length) const {
     const FilterInstance& filter = filters_[value_offset];
     *filter_offset = filter.offset;
-    *filter_length = filter.length;
-    if (filter.length == 0) {
+    *filter_length = filter.trimmed_length;
+    if (filter.trimmed_length == 0) {
       return NULL;
     }
     return &filter_values_[filter.data_location];
   }
 
+  // Retrieves the filter for the offset 0, presumed to be the one and only.
+  // The offset and length of the filter values are put into the corresponding
+  // out arguments (see AddFilter). Note that |filter_legth| and
+  // |specified_filter_length| may be different if leading/trailing zeros of the
+  // original floating point form were clipped.
+  // There will be |filter_length| values in the return array.
+  // Returns NULL if the filter is 0-length (for instance when all floating
+  // point values passed to AddFilter were clipped to 0).
+  const Fixed* GetSingleFilter(int* specified_filter_length,
+                               int* filter_offset,
+                               int* filter_length) const;
 
   inline void PaddingForSIMD() {
     // Padding |padding_count| of more dummy coefficients after the coefficients
     // of last filter to prevent SIMD instructions which load 8 or 16 bytes
     // together to access invalid memory areas. We are not trying to align the
     // coefficients right now due to the opaqueness of <vector> implementation.
     // This has to be done after all |AddFilter| calls.
 #ifdef SIMD_PADDING
     for (int i = 0; i < SIMD_PADDING; ++i)
       filter_values_.push_back(static_cast<Fixed>(0));
 #endif
   }
 
  private:
   struct FilterInstance {
     // Offset within filter_values for this instance of the filter.
     int data_location;
 
     // Distance from the left of the filter to the center. IN PIXELS
     int offset;
 
     // Number of values in this filter instance.
+    int trimmed_length;
+
+    // Filter length as specified. Note that this may be different from
+    // 'trimmed_length' if leading/trailing zeros of the original floating
+    // point form were clipped differently on each tail.
     int length;
   };
 
   // Stores the information for each filter added to this class.
   std::vector<FilterInstance> filters_;
 
   // We store all the filter values in this flat list, indexed by
   // |FilterInstance.data_location| to avoid the mallocs required for storing
   // each one separately.
   std::vector<Fixed> filter_values_;
@@ skipping 21 matching lines @@
 // The layout in memory is assumed to be 4-bytes per pixel in B-G-R-A order
 // (this is ARGB when loaded into 32-bit words on a little-endian machine).
 SK_API void BGRAConvolve2D(const unsigned char* source_data,
                            int source_byte_row_stride,
                            bool source_has_alpha,
                            const ConvolutionFilter1D& xfilter,
                            const ConvolutionFilter1D& yfilter,
                            int output_byte_row_stride,
                            unsigned char* output,
                            bool use_simd_if_possible);
+
+// Does a 1D convolution of the given source image along the X dimension on
+// a single channel of the bitmap.
+//
+// The function uses the same convolution kernel for each pixel. That kernel
+// must be added to |filter| at offset 0. This is a most straightforward
+// implementation of convolution, intended chiefly for development purposes.
+SK_API void SingleChannelConvolveX1D(const unsigned char* source_data,
+                                     int source_byte_row_stride,
+                                     int input_channel_index,
+                                     int input_channel_count,
+                                     const ConvolutionFilter1D& filter,
+                                     const SkISize& image_size,
+                                     unsigned char* output,
+                                     int output_byte_row_stride,
+                                     int output_channel_index,
+                                     int output_channel_count,
+                                     bool absolute_values);
+
+// Does a 1D convolution of the given source image along the Y dimension on
+// a single channel of the bitmap.
+SK_API void SingleChannelConvolveY1D(const unsigned char* source_data,
+                                     int source_byte_row_stride,
+                                     int input_channel_index,
+                                     int input_channel_count,
+                                     const ConvolutionFilter1D& filter,
+                                     const SkISize& image_size,
+                                     unsigned char* output,
+                                     int output_byte_row_stride,
+                                     int output_channel_index,
+                                     int output_channel_count,
+                                     bool absolute_values);
+
 }  // namespace skia
 
 #endif  // SKIA_EXT_CONVOLVER_H_