| // 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 |
| |