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-rw-r--r--base/gfx/convolver.cc335
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diff --git a/base/gfx/convolver.cc b/base/gfx/convolver.cc
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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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