github.com/cellofellow/gopkg@v0.0.0-20140722061823-eec0544a62ad/image/webp/libwebp/src/utils/rescaler.h (about)

     1  // Copyright 2012 Google Inc. All Rights Reserved.
     2  //
     3  // Use of this source code is governed by a BSD-style license
     4  // that can be found in the COPYING file in the root of the source
     5  // tree. An additional intellectual property rights grant can be found
     6  // in the file PATENTS. All contributing project authors may
     7  // be found in the AUTHORS file in the root of the source tree.
     8  // -----------------------------------------------------------------------------
     9  //
    10  // Rescaling functions
    11  //
    12  // Author: Skal (pascal.massimino@gmail.com)
    13  
    14  #ifndef WEBP_UTILS_RESCALER_H_
    15  #define WEBP_UTILS_RESCALER_H_
    16  
    17  #ifdef __cplusplus
    18  extern "C" {
    19  #endif
    20  
    21  #include "../webp/types.h"
    22  
    23  // Structure used for on-the-fly rescaling
    24  typedef struct {
    25    int x_expand;               // true if we're expanding in the x direction
    26    int num_channels;           // bytes to jump between pixels
    27    int fy_scale, fx_scale;     // fixed-point scaling factor
    28    int64_t fxy_scale;          // ''
    29    // we need hpel-precise add/sub increments, for the downsampled U/V planes.
    30    int y_accum;                // vertical accumulator
    31    int y_add, y_sub;           // vertical increments (add ~= src, sub ~= dst)
    32    int x_add, x_sub;           // horizontal increments (add ~= src, sub ~= dst)
    33    int src_width, src_height;  // source dimensions
    34    int dst_width, dst_height;  // destination dimensions
    35    uint8_t* dst;
    36    int dst_stride;
    37    int32_t* irow, *frow;       // work buffer
    38  } WebPRescaler;
    39  
    40  // Initialize a rescaler given scratch area 'work' and dimensions of src & dst.
    41  void WebPRescalerInit(WebPRescaler* const rescaler,
    42                        int src_width, int src_height,
    43                        uint8_t* const dst,
    44                        int dst_width, int dst_height, int dst_stride,
    45                        int num_channels,
    46                        int x_add, int x_sub,
    47                        int y_add, int y_sub,
    48                        int32_t* const work);
    49  
    50  // Returns the number of input lines needed next to produce one output line,
    51  // considering that the maximum available input lines are 'max_num_lines'.
    52  int WebPRescaleNeededLines(const WebPRescaler* const rescaler,
    53                             int max_num_lines);
    54  
    55  // Import a row of data and save its contribution in the rescaler.
    56  // 'channel' denotes the channel number to be imported.
    57  void WebPRescalerImportRow(WebPRescaler* const rescaler,
    58                             const uint8_t* const src, int channel);
    59  
    60  // Import multiple rows over all channels, until at least one row is ready to
    61  // be exported. Returns the actual number of lines that were imported.
    62  int WebPRescalerImport(WebPRescaler* const rescaler, int num_rows,
    63                         const uint8_t* src, int src_stride);
    64  
    65  // Return true if there is pending output rows ready.
    66  static WEBP_INLINE
    67  int WebPRescalerHasPendingOutput(const WebPRescaler* const rescaler) {
    68    return (rescaler->y_accum <= 0);
    69  }
    70  
    71  // Export one row from rescaler. Returns the pointer where output was written,
    72  // or NULL if no row was pending.
    73  uint8_t* WebPRescalerExportRow(WebPRescaler* const rescaler);
    74  
    75  // Export as many rows as possible. Return the numbers of rows written.
    76  int WebPRescalerExport(WebPRescaler* const rescaler);
    77  
    78  //------------------------------------------------------------------------------
    79  
    80  #ifdef __cplusplus
    81  }    // extern "C"
    82  #endif
    83  
    84  #endif  /* WEBP_UTILS_RESCALER_H_ */