rescaler_utils.c
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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 (pascal.massimino@gmail.com)
#include <assert.h>
#include <stdlib.h>
#include <string.h>
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#include "src/dsp/dsp.h"
#include "src/utils/rescaler_utils.h"
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//------------------------------------------------------------------------------
void WebPRescalerInit(WebPRescaler* const wrk, 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) {
const int x_add = src_width, x_sub = dst_width;
const int y_add = src_height, y_sub = dst_height;
wrk->x_expand = (src_width < dst_width);
wrk->y_expand = (src_height < dst_height);
wrk->src_width = src_width;
wrk->src_height = src_height;
wrk->dst_width = dst_width;
wrk->dst_height = dst_height;
wrk->src_y = 0;
wrk->dst_y = 0;
wrk->dst = dst;
wrk->dst_stride = dst_stride;
wrk->num_channels = num_channels;
// for 'x_expand', we use bilinear interpolation
wrk->x_add = wrk->x_expand ? (x_sub - 1) : x_add;
wrk->x_sub = wrk->x_expand ? (x_add - 1) : x_sub;
if (!wrk->x_expand) { // fx_scale is not used otherwise
wrk->fx_scale = WEBP_RESCALER_FRAC(1, wrk->x_sub);
}
// vertical scaling parameters
wrk->y_add = wrk->y_expand ? y_add - 1 : y_add;
wrk->y_sub = wrk->y_expand ? y_sub - 1 : y_sub;
wrk->y_accum = wrk->y_expand ? wrk->y_sub : wrk->y_add;
if (!wrk->y_expand) {
// This is WEBP_RESCALER_FRAC(dst_height, x_add * y_add) without the cast.
// Its value is <= WEBP_RESCALER_ONE, because dst_height <= wrk->y_add, and
// wrk->x_add >= 1;
const uint64_t ratio =
(uint64_t)dst_height * WEBP_RESCALER_ONE / (wrk->x_add * wrk->y_add);
if (ratio != (uint32_t)ratio) {
// When ratio == WEBP_RESCALER_ONE, we can't represent the ratio with the
// current fixed-point precision. This happens when src_height ==
// wrk->y_add (which == src_height), and wrk->x_add == 1.
// => We special-case fxy_scale = 0, in WebPRescalerExportRow().
wrk->fxy_scale = 0;
} else {
wrk->fxy_scale = (uint32_t)ratio;
}
wrk->fy_scale = WEBP_RESCALER_FRAC(1, wrk->y_sub);
} else {
wrk->fy_scale = WEBP_RESCALER_FRAC(1, wrk->x_add);
// wrk->fxy_scale is unused here.
}
wrk->irow = work;
wrk->frow = work + num_channels * dst_width;
memset(work, 0, 2 * dst_width * num_channels * sizeof(*work));
WebPRescalerDspInit();
}
int WebPRescalerGetScaledDimensions(int src_width, int src_height,
int* const scaled_width,
int* const scaled_height) {
assert(scaled_width != NULL);
assert(scaled_height != NULL);
{
int width = *scaled_width;
int height = *scaled_height;
// if width is unspecified, scale original proportionally to height ratio.
if (width == 0) {
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width =
(int)(((uint64_t)src_width * height + src_height / 2) / src_height);
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}
// if height is unspecified, scale original proportionally to width ratio.
if (height == 0) {
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height =
(int)(((uint64_t)src_height * width + src_width / 2) / src_width);
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}
// Check if the overall dimensions still make sense.
if (width <= 0 || height <= 0) {
return 0;
}
*scaled_width = width;
*scaled_height = height;
return 1;
}
}
//------------------------------------------------------------------------------
// all-in-one calls
int WebPRescaleNeededLines(const WebPRescaler* const wrk, int max_num_lines) {
const int num_lines = (wrk->y_accum + wrk->y_sub - 1) / wrk->y_sub;
return (num_lines > max_num_lines) ? max_num_lines : num_lines;
}
int WebPRescalerImport(WebPRescaler* const wrk, int num_lines,
const uint8_t* src, int src_stride) {
int total_imported = 0;
while (total_imported < num_lines && !WebPRescalerHasPendingOutput(wrk)) {
if (wrk->y_expand) {
rescaler_t* const tmp = wrk->irow;
wrk->irow = wrk->frow;
wrk->frow = tmp;
}
WebPRescalerImportRow(wrk, src);
if (!wrk->y_expand) { // Accumulate the contribution of the new row.
int x;
for (x = 0; x < wrk->num_channels * wrk->dst_width; ++x) {
wrk->irow[x] += wrk->frow[x];
}
}
++wrk->src_y;
src += src_stride;
++total_imported;
wrk->y_accum -= wrk->y_sub;
}
return total_imported;
}
int WebPRescalerExport(WebPRescaler* const rescaler) {
int total_exported = 0;
while (WebPRescalerHasPendingOutput(rescaler)) {
WebPRescalerExportRow(rescaler);
++total_exported;
}
return total_exported;
}
//------------------------------------------------------------------------------