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+// 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/gfx/convolver.h"
+#include "base/logging.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
+
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