Pillow

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/*
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 * The Python Imaging Library
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 * $Id$
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 *
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 * offset an image in x and y directions
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 *
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 * history:
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 * 96-07-22 fl: Created
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 * 98-11-01 cgw@pgt.com: Fixed negative-array index bug
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 *
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 * Copyright (c) Fredrik Lundh 1996.
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 * Copyright (c) Secret Labs AB 1997.
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 *
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 * See the README file for information on usage and redistribution.
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 */
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#include "Imaging.h"
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Imaging
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ImagingOffset(Imaging im, int xoffset, int yoffset) {
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    int x, y;
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    Imaging imOut;
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    if (!im) {
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        return (Imaging)ImagingError_ModeError();
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    }
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    imOut = ImagingNewDirty(im->mode, im->xsize, im->ysize);
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    if (!imOut) {
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        return NULL;
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    }
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    ImagingCopyPalette(imOut, im);
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    /* make offsets positive to avoid negative coordinates */
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    xoffset %= im->xsize;
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    xoffset = im->xsize - xoffset;
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    if (xoffset < 0) {
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        xoffset += im->xsize;
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    }
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    yoffset %= im->ysize;
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    yoffset = im->ysize - yoffset;
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    if (yoffset < 0) {
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        yoffset += im->ysize;
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    }
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#define OFFSET(image)                               \
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    for (y = 0; y < im->ysize; y++) {               \
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        for (x = 0; x < im->xsize; x++) {           \
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            int yi = (y + yoffset) % im->ysize;     \
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            int xi = (x + xoffset) % im->xsize;     \
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            imOut->image[y][x] = im->image[yi][xi]; \
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        }                                           \
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    }
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    if (im->image8) {
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        OFFSET(image8)
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    } else {
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        OFFSET(image32)
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    }
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    return imOut;
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}
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