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// Copyright 2012 Google Inc. All Rights Reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
// Rescaling functions
// Author: Skal (
#ifdef __cplusplus
extern "C" {
#include "../webp/types.h"
#define WEBP_RESCALER_RFIX 32 // fixed-point precision for multiplies
#define WEBP_RESCALER_FRAC(x, y) \
((uint32_t)(((uint64_t)(x) << WEBP_RESCALER_RFIX) / (y)))
// Structure used for on-the-fly rescaling
typedef uint32_t rescaler_t; // type for side-buffer
typedef struct WebPRescaler WebPRescaler;
struct WebPRescaler {
int x_expand; // true if we're expanding in the x direction
int y_expand; // true if we're expanding in the y direction
int num_channels; // bytes to jump between pixels
uint32_t fx_scale; // fixed-point scaling factors
uint32_t fy_scale; // ''
uint32_t fxy_scale; // ''
int y_accum; // vertical accumulator
int y_add, y_sub; // vertical increments
int x_add, x_sub; // horizontal increments
int src_width, src_height; // source dimensions
int dst_width, dst_height; // destination dimensions
int src_y, dst_y; // row counters for input and output
uint8_t* dst;
int dst_stride;
rescaler_t* irow, *frow; // work buffer
// Initialize a rescaler given scratch area 'work' and dimensions of src & dst.
void WebPRescalerInit(WebPRescaler* const rescaler,
int src_width, int src_height,
uint8_t* const dst,
int dst_width, int dst_height, int dst_stride,
int num_channels,
rescaler_t* const work);
// If either 'scaled_width' or 'scaled_height' (but not both) is 0 the value
// will be calculated preserving the aspect ratio, otherwise the values are
// left unmodified. Returns true on success, false if either value is 0 after
// performing the scaling calculation.
int WebPRescalerGetScaledDimensions(int src_width, int src_height,
int* const scaled_width,
int* const scaled_height);
// Returns the number of input lines needed next to produce one output line,
// considering that the maximum available input lines are 'max_num_lines'.
int WebPRescaleNeededLines(const WebPRescaler* const rescaler,
int max_num_lines);
// Import multiple rows over all channels, until at least one row is ready to
// be exported. Returns the actual number of lines that were imported.
int WebPRescalerImport(WebPRescaler* const rescaler, int num_rows,
const uint8_t* src, int src_stride);
// Export as many rows as possible. Return the numbers of rows written.
int WebPRescalerExport(WebPRescaler* const rescaler);
// Return true if input is finished
int WebPRescalerInputDone(const WebPRescaler* const rescaler) {
return (rescaler->src_y >= rescaler->src_height);
// Return true if output is finished
int WebPRescalerOutputDone(const WebPRescaler* const rescaler) {
return (rescaler->dst_y >= rescaler->dst_height);
// Return true if there are pending output rows ready.
int WebPRescalerHasPendingOutput(const WebPRescaler* const rescaler) {
return !WebPRescalerOutputDone(rescaler) && (rescaler->y_accum <= 0);
#ifdef __cplusplus
} // extern "C"