Move convolver and image_operations from base/gfx to skia/ext. This is just

like my previous change except does no namespace renaming and doesn't touch
skia_utils.
Review URL: http://codereview.chromium.org/13080

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@6290 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 335 insertions, 0 deletions

diff --git a/skia/ext/convolver.cc b/skia/ext/convolver.cc
new file mode 100644
index 0000000..f5a429a
--- /dev/null
+++ b/skia/ext/convolver.cc
@@ -0,0 +1,335 @@
+// Copyright (c) 2006-2008 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.
+
+#include <algorithm>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "skia/ext/convolver.h"
+
+namespace gfx {
+
+namespace {
+
+// Converts the argument to an 8-bit unsigned value by clamping to the range
+// 0-255.
+inline uint8 ClampTo8(int32 a) {
+  if (static_cast<uint32>(a) < 256)
+    return a;  // Avoid the extra check in the common case.
+  if (a < 0)
+    return 0;
+  return 255;
+}
+
+// Stores a list of rows in a circular buffer. The usage is you write into it
+// by calling AdvanceRow. It will keep track of which row in the buffer it
+// should use next, and the total number of rows added.
+class CircularRowBuffer {
+ public:
+  // The number of pixels in each row is given in |source_row_pixel_width|.
+  // The maximum number of rows needed in the buffer is |max_y_filter_size|
+  // (we only need to store enough rows for the biggest filter).
+  //
+  // We use the |first_input_row| to compute the coordinates of all of the
+  // following rows returned by Advance().
+  CircularRowBuffer(int dest_row_pixel_width, int max_y_filter_size,
+                    int first_input_row)
+      : row_byte_width_(dest_row_pixel_width * 4),
+        num_rows_(max_y_filter_size),
+        next_row_(0),
+        next_row_coordinate_(first_input_row) {
+    buffer_.resize(row_byte_width_ * max_y_filter_size);
+    row_addresses_.resize(num_rows_);
+  }
+
+  // Moves to the next row in the buffer, returning a pointer to the beginning
+  // of it.
+  uint8* AdvanceRow() {
+    uint8* row = &buffer_[next_row_ * row_byte_width_];
+    next_row_coordinate_++;
+
+    // Set the pointer to the next row to use, wrapping around if necessary.
+    next_row_++;
+    if (next_row_ == num_rows_)
+      next_row_ = 0;
+    return row;
+  }
+
+  // Returns a pointer to an "unrolled" array of rows. These rows will start
+  // at the y coordinate placed into |*first_row_index| and will continue in
+  // order for the maximum number of rows in this circular buffer.
+  //
+  // The |first_row_index_| may be negative. This means the circular buffer
+  // starts before the top of the image (it hasn't been filled yet).
+  uint8* const* GetRowAddresses(int* first_row_index) {
+    // Example for a 4-element circular buffer holding coords 6-9.
+    //   Row 0   Coord 8
+    //   Row 1   Coord 9
+    //   Row 2   Coord 6  <- next_row_ = 2, next_row_coordinate_ = 10.
+    //   Row 3   Coord 7
+    //
+    // The "next" row is also the first (lowest) coordinate. This computation
+    // may yield a negative value, but that's OK, the math will work out
+    // since the user of this buffer will compute the offset relative
+    // to the first_row_index and the negative rows will never be used.
+    *first_row_index = next_row_coordinate_ - num_rows_;
+
+    int cur_row = next_row_;
+    for (int i = 0; i < num_rows_; i++) {
+      row_addresses_[i] = &buffer_[cur_row * row_byte_width_];
+
+      // Advance to the next row, wrapping if necessary.
+      cur_row++;
+      if (cur_row == num_rows_)
+        cur_row = 0;
+    }
+    return &row_addresses_[0];
+  }
+
+ private:
+  // The buffer storing the rows. They are packed, each one row_byte_width_.
+  std::vector<uint8> buffer_;
+
+  // Number of bytes per row in the |buffer_|.
+  int row_byte_width_;
+
+  // The number of rows available in the buffer.
+  int num_rows_;
+
+  // The next row index we should write into. This wraps around as the
+  // circular buffer is used.
+  int next_row_;
+
+  // The y coordinate of the |next_row_|. This is incremented each time a
+  // new row is appended and does not wrap.
+  int next_row_coordinate_;
+
+  // Buffer used by GetRowAddresses().
+  std::vector<uint8*> row_addresses_;
+};
+
+// Convolves horizontally along a single row. The row data is given in
+// |src_data| and continues for the num_values() of the filter.
+template<bool has_alpha>
+void ConvolveHorizontally(const uint8* src_data,
+                          const ConvolusionFilter1D& filter,
+                          unsigned char* out_row) {
+  // Loop over each pixel on this row in the output image.
+  int num_values = filter.num_values();
+  for (int out_x = 0; out_x < num_values; out_x++) {
+    // Get the filter that determines the current output pixel.
+    int filter_offset, filter_length;
+    const int16* filter_values =
+        filter.FilterForValue(out_x, &filter_offset, &filter_length);
+
+    // Compute the first pixel in this row that the filter affects. It will
+    // touch |filter_length| pixels (4 bytes each) after this.
+    const uint8* row_to_filter = &src_data[filter_offset * 4];
+
+    // Apply the filter to the row to get the destination pixel in |accum|.
+    int32 accum[4] = {0};
+    for (int filter_x = 0; filter_x < filter_length; filter_x++) {
+      int16 cur_filter = filter_values[filter_x];
+      accum[0] += cur_filter * row_to_filter[filter_x * 4 + 0];
+      accum[1] += cur_filter * row_to_filter[filter_x * 4 + 1];
+      accum[2] += cur_filter * row_to_filter[filter_x * 4 + 2];
+      if (has_alpha)
+        accum[3] += cur_filter * row_to_filter[filter_x * 4 + 3];
+    }
+
+    // Bring this value back in range. All of the filter scaling factors
+    // are in fixed point with kShiftBits bits of fractional part.
+    accum[0] >>= ConvolusionFilter1D::kShiftBits;
+    accum[1] >>= ConvolusionFilter1D::kShiftBits;
+    accum[2] >>= ConvolusionFilter1D::kShiftBits;
+    if (has_alpha)
+      accum[3] >>= ConvolusionFilter1D::kShiftBits;
+
+    // Store the new pixel.
+    out_row[out_x * 4 + 0] = ClampTo8(accum[0]);
+    out_row[out_x * 4 + 1] = ClampTo8(accum[1]);
+    out_row[out_x * 4 + 2] = ClampTo8(accum[2]);
+    if (has_alpha)
+      out_row[out_x * 4 + 3] = ClampTo8(accum[3]);
+  }
+}
+
+// Does vertical convolusion to produce one output row. The filter values and
+// length are given in the first two parameters. These are applied to each
+// of the rows pointed to in the |source_data_rows| array, with each row
+// being |pixel_width| wide.
+//
+// The output must have room for |pixel_width * 4| bytes.
+template<bool has_alpha>
+void ConvolveVertically(const int16* filter_values,
+                        int filter_length,
+                        uint8* const* source_data_rows,
+                        int pixel_width,
+                        uint8* out_row) {
+  // We go through each column in the output and do a vertical convolusion,
+  // generating one output pixel each time.
+  for (int out_x = 0; out_x < pixel_width; out_x++) {
+    // Compute the number of bytes over in each row that the current column
+    // we're convolving starts at. The pixel will cover the next 4 bytes.
+    int byte_offset = out_x * 4;
+
+    // Apply the filter to one column of pixels.
+    int32 accum[4] = {0};
+    for (int filter_y = 0; filter_y < filter_length; filter_y++) {
+      int16 cur_filter = filter_values[filter_y];
+      accum[0] += cur_filter * source_data_rows[filter_y][byte_offset + 0];
+      accum[1] += cur_filter * source_data_rows[filter_y][byte_offset + 1];
+      accum[2] += cur_filter * source_data_rows[filter_y][byte_offset + 2];
+      if (has_alpha)
+        accum[3] += cur_filter * source_data_rows[filter_y][byte_offset + 3];
+    }
+
+    // Bring this value back in range. All of the filter scaling factors
+    // are in fixed point with kShiftBits bits of precision.
+    accum[0] >>= ConvolusionFilter1D::kShiftBits;
+    accum[1] >>= ConvolusionFilter1D::kShiftBits;
+    accum[2] >>= ConvolusionFilter1D::kShiftBits;
+    if (has_alpha)
+      accum[3] >>= ConvolusionFilter1D::kShiftBits;
+
+    // Store the new pixel.
+    out_row[byte_offset + 0] = ClampTo8(accum[0]);
+    out_row[byte_offset + 1] = ClampTo8(accum[1]);
+    out_row[byte_offset + 2] = ClampTo8(accum[2]);
+    if (has_alpha) {
+      uint8 alpha = ClampTo8(accum[3]);
+
+      // Make sure the alpha channel doesn't come out larger than any of the
+      // color channels. We use premultipled alpha channels, so this should
+      // never happen, but rounding errors will cause this from time to time.
+      // These "impossible" colors will cause overflows (and hence random pixel
+      // values) when the resulting bitmap is drawn to the screen.
+      //
+      // We only need to do this when generating the final output row (here).
+      int max_color_channel = std::max(out_row[byte_offset + 0],
+          std::max(out_row[byte_offset + 1], out_row[byte_offset + 2]));
+      if (alpha < max_color_channel)
+        out_row[byte_offset + 3] = max_color_channel;
+      else
+        out_row[byte_offset + 3] = alpha;
+    } else {
+      // No alpha channel, the image is opaque.
+      out_row[byte_offset + 3] = 0xff;
+    }
+  }
+}
+
+}  // namespace
+
+// ConvolusionFilter1D ---------------------------------------------------------
+
+void ConvolusionFilter1D::AddFilter(int filter_offset,
+                                    const float* filter_values,
+                                    int filter_length) {
+  FilterInstance instance;
+  instance.data_location = static_cast<int>(filter_values_.size());
+  instance.offset = filter_offset;
+  instance.length = filter_length;
+  filters_.push_back(instance);
+
+  DCHECK(filter_length > 0);
+  for (int i = 0; i < filter_length; i++)
+    filter_values_.push_back(FloatToFixed(filter_values[i]));
+
+  max_filter_ = std::max(max_filter_, filter_length);
+}
+
+void ConvolusionFilter1D::AddFilter(int filter_offset,
+                                    const int16* filter_values,
+                                    int filter_length) {
+  FilterInstance instance;
+  instance.data_location = static_cast<int>(filter_values_.size());
+  instance.offset = filter_offset;
+  instance.length = filter_length;
+  filters_.push_back(instance);
+
+  DCHECK(filter_length > 0);
+  for (int i = 0; i < filter_length; i++)
+    filter_values_.push_back(filter_values[i]);
+
+  max_filter_ = std::max(max_filter_, filter_length);
+}
+
+// BGRAConvolve2D -------------------------------------------------------------
+
+void BGRAConvolve2D(const uint8* source_data,
+                    int source_byte_row_stride,
+                    bool source_has_alpha,
+                    const ConvolusionFilter1D& filter_x,
+                    const ConvolusionFilter1D& filter_y,
+                    uint8* output) {
+  int max_y_filter_size = filter_y.max_filter();
+
+  // The next row in the input that we will generate a horizontally
+  // convolved row for. If the filter doesn't start at the beginning of the
+  // image (this is the case when we are only resizing a subset), then we
+  // don't want to generate any output rows before that. Compute the starting
+  // row for convolusion as the first pixel for the first vertical filter.
+  int filter_offset, filter_length;
+  const int16* filter_values =
+      filter_y.FilterForValue(0, &filter_offset, &filter_length);
+  int next_x_row = filter_offset;
+
+  // We loop over each row in the input doing a horizontal convolusion. This
+  // will result in a horizontally convolved image. We write the results into
+  // a circular buffer of convolved rows and do vertical convolusion as rows
+  // are available. This prevents us from having to store the entire
+  // intermediate image and helps cache coherency.
+  CircularRowBuffer row_buffer(filter_x.num_values(), max_y_filter_size,
+                               filter_offset);
+
+  // Loop over every possible output row, processing just enough horizontal
+  // convolusions to run each subsequent vertical convolusion.
+  int output_row_byte_width = filter_x.num_values() * 4;
+  int num_output_rows = filter_y.num_values();
+  for (int out_y = 0; out_y < num_output_rows; out_y++) {
+    filter_values = filter_y.FilterForValue(out_y,
+                                            &filter_offset, &filter_length);
+
+    // Generate output rows until we have enough to run the current filter.
+    while (next_x_row < filter_offset + filter_length) {
+      if (source_has_alpha) {
+        ConvolveHorizontally<true>(
+            &source_data[next_x_row * source_byte_row_stride],
+            filter_x, row_buffer.AdvanceRow());
+      } else {
+        ConvolveHorizontally<false>(
+            &source_data[next_x_row * source_byte_row_stride],
+            filter_x, row_buffer.AdvanceRow());
+      }
+      next_x_row++;
+    }
+
+    // Compute where in the output image this row of final data will go.
+    uint8* cur_output_row = &output[out_y * output_row_byte_width];
+
+    // Get the list of rows that the circular buffer has, in order.
+    int first_row_in_circular_buffer;
+    uint8* const* rows_to_convolve =
+        row_buffer.GetRowAddresses(&first_row_in_circular_buffer);
+
+    // Now compute the start of the subset of those rows that the filter
+    // needs.
+    uint8* const* first_row_for_filter =
+        &rows_to_convolve[filter_offset - first_row_in_circular_buffer];
+
+    if (source_has_alpha) {
+      ConvolveVertically<true>(filter_values, filter_length,
+                               first_row_for_filter,
+                               filter_x.num_values(), cur_output_row);
+    } else {
+      ConvolveVertically<false>(filter_values, filter_length,
+                                first_row_for_filter,
+                                filter_x.num_values(), cur_output_row);
+    }
+  }
+}
+
+}  // namespace gfx
+