Pillow/src/libImaging/Offset.c

/*
 * The Python Imaging Library
 * $Id$
 *
 * offset an image in x and y directions
 *
 * history:
 * 96-07-22 fl: Created
 * 98-11-01 cgw@pgt.com: Fixed negative-array index bug
 *
 * Copyright (c) Fredrik Lundh 1996.
 * Copyright (c) Secret Labs AB 1997.
 *
 * See the README file for information on usage and redistribution.
 */

#include "Imaging.h"

Imaging
ImagingOffset(Imaging im, int xoffset, int yoffset) {
    int x, y;
    Imaging imOut;

    if (!im) {
        return (Imaging)ImagingError_ModeError();
    }

    imOut = ImagingNewDirty(im->mode, im->xsize, im->ysize);
    if (!imOut) {
        return NULL;
    }

    ImagingCopyPalette(imOut, im);

    /* make offsets positive to avoid negative coordinates */
    xoffset %= im->xsize;
    xoffset = im->xsize - xoffset;
    if (xoffset < 0) {
        xoffset += im->xsize;
    }

    yoffset %= im->ysize;
    yoffset = im->ysize - yoffset;
    if (yoffset < 0) {
        yoffset += im->ysize;
    }

#define OFFSET(image)                               \
    for (y = 0; y < im->ysize; y++) {               \
        for (x = 0; x < im->xsize; x++) {           \
            int yi = (y + yoffset) % im->ysize;     \
            int xi = (x + xoffset) % im->xsize;     \
            imOut->image[y][x] = im->image[yi][xi]; \
        }                                           \
    }

    if (im->image8) {
        OFFSET(image8)
    } else {
        OFFSET(image32)
    }

    return imOut;
}