Minecraft-Overviewer/overviewer_core/src/composite.c

/* 
 * This file is part of the Minecraft Overviewer.
 *
 * Minecraft Overviewer is free software: you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or (at
 * your option) any later version.
 *
 * Minecraft Overviewer is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
 * Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
 */

/* 
 * This file implements a custom alpha_over function for (some) PIL
 * images. It's designed to be used through composite.py, which
 * includes a proxy alpha_over function that falls back to the default
 * PIL paste if this extension is not found.
 */

#include "overviewer.h"

/* like (a * b + 127) / 255), but much faster on most platforms
   from PIL's _imaging.c */
#define MULDIV255(a, b, tmp)								\
	(tmp = (a) * (b) + 128, ((((tmp) >> 8) + (tmp)) >> 8))

typedef struct {
    PyObject_HEAD
    Imaging image;
} ImagingObject;

inline Imaging
imaging_python_to_c(PyObject *obj)
{
    PyObject *im;
    Imaging image;

    /* first, get the 'im' attribute */
    im = PyObject_GetAttrString(obj, "im");
    if (!im)
        return NULL;

    /* make sure 'im' is the right type */
    if (strcmp(im->ob_type->tp_name, "ImagingCore") != 0) {
        /* it's not -- raise an error and exit */
        PyErr_SetString(PyExc_TypeError,
                        "image attribute 'im' is not a core Imaging type");
        return NULL;
    }

    image = ((ImagingObject *)im)->image;
    Py_DECREF(im);
    return image;
}

/* helper function to setup s{x,y}, d{x,y}, and {x,y}size variables
   in these composite functions -- even handles auto-sizing to src! */
static inline void
setup_source_destination(Imaging src, Imaging dest,
                         int *sx, int *sy, int *dx, int *dy, int *xsize, int *ysize)
{
   /* handle negative/zero sizes appropriately */
    if (*xsize <= 0 || *ysize <= 0) {
        *xsize = src->xsize;
        *ysize = src->ysize;
    }
    
    /* set up the source position, size and destination position */
    /* handle negative dest pos */
    if (*dx < 0) {
        *sx = -(*dx);
        *dx = 0;
    } else {
        *sx = 0;
    }

    if (*dy < 0) {
        *sy = -(*dy);
        *dy = 0;
    } else {
        *sy = 0;
    }

    /* set up source dimensions */
    *xsize -= *sx;
    *ysize -= *sy;

    /* clip dimensions, if needed */
    if (*dx + *xsize > dest->xsize)
        *xsize = dest->xsize - *dx;
    if (*dy + *ysize > dest->ysize)
        *ysize = dest->ysize - *dy;
}

/* convenience alpha_over with 1.0 as overall_alpha */
inline PyObject* alpha_over(PyObject *dest, PyObject *src, PyObject *mask,
                            int dx, int dy, int xsize, int ysize) {
    return alpha_over_full(dest, src, mask, 1.0f, dx, dy, xsize, ysize);
}

/* the full alpha_over function, in a form that can be called from C
 * overall_alpha is multiplied with the whole mask, useful for lighting...
 * if xsize, ysize are negative, they are instead set to the size of the image in src
 * returns NULL on error, dest on success. You do NOT need to decref the return!
 */
inline PyObject *
alpha_over_full(PyObject *dest, PyObject *src, PyObject *mask, float overall_alpha,
                int dx, int dy, int xsize, int ysize) {
    /* libImaging handles */
    Imaging imDest, imSrc, imMask;
    /* cached blend properties */
    int src_has_alpha, mask_offset, mask_stride;
    /* source position */
    int sx, sy;
    /* iteration variables */
    unsigned int x, y, i;
    /* temporary calculation variables */
    int tmp1, tmp2, tmp3;
    /* integer [0, 255] version of overall_alpha */
    UINT8 overall_alpha_int = 255 * overall_alpha;
    
    /* short-circuit this whole thing if overall_alpha is zero */
    if (overall_alpha_int == 0)
        return dest;

    imDest = imaging_python_to_c(dest);
    imSrc = imaging_python_to_c(src);
    imMask = imaging_python_to_c(mask);

    if (!imDest || !imSrc || !imMask)
        return NULL;

    /* check the various image modes, make sure they make sense */
    if (strcmp(imDest->mode, "RGBA") != 0) {
        PyErr_SetString(PyExc_ValueError,
                        "given destination image does not have mode \"RGBA\"");
        return NULL;
    }

    if (strcmp(imSrc->mode, "RGBA") != 0 && strcmp(imSrc->mode, "RGB") != 0) {
        PyErr_SetString(PyExc_ValueError,
                        "given source image does not have mode \"RGBA\" or \"RGB\"");
        return NULL;
    }

    if (strcmp(imMask->mode, "RGBA") != 0 && strcmp(imMask->mode, "L") != 0) {
        PyErr_SetString(PyExc_ValueError,
                        "given mask image does not have mode \"RGBA\" or \"L\"");
        return NULL;
    }

    /* make sure mask size matches src size */
    if (imSrc->xsize != imMask->xsize || imSrc->ysize != imMask->ysize) {
        PyErr_SetString(PyExc_ValueError,
                        "mask and source image sizes do not match");
        return NULL;
    }

    /* set up flags for the src/mask type */
    src_has_alpha = (imSrc->pixelsize == 4 ? 1 : 0);
    /* how far into image the first alpha byte resides */
    mask_offset = (imMask->pixelsize == 4 ? 3 : 0);
    /* how many bytes to skip to get to the next alpha byte */
    mask_stride = imMask->pixelsize;

    /* setup source & destination vars */
    setup_source_destination(imSrc, imDest, &sx, &sy, &dx, &dy, &xsize, &ysize);

    /* check that there remains any blending to be done */
    if (xsize <= 0 || ysize <= 0) {
        /* nothing to do, return */
        return dest;
    }

    for (y = 0; y < ysize; y++) {
        UINT8 *out = (UINT8 *)imDest->image[dy + y] + dx * 4;
        UINT8 *outmask = (UINT8 *)imDest->image[dy + y] + dx * 4 + 3;
        UINT8 *in = (UINT8 *)imSrc->image[sy + y] + sx * (imSrc->pixelsize);
        UINT8 *inmask = (UINT8 *)imMask->image[sy + y] + sx * mask_stride + mask_offset;

        for (x = 0; x < xsize; x++) {
            UINT8 in_alpha;
            
            /* apply overall_alpha */
            if (overall_alpha_int != 255 && *inmask != 0) {
                in_alpha = MULDIV255(*inmask, overall_alpha_int, tmp1);
            } else {
                in_alpha = *inmask;
            }
            
            /* special cases */
            if (in_alpha == 255 || *outmask == 0) {
                *outmask = in_alpha;

                *out = *in;
                out++, in++;
                *out = *in;
                out++, in++;
                *out = *in;
                out++, in++;
            } else if (in_alpha == 0) {
                /* do nothing -- source is fully transparent */
                out += 3;
                in += 3;
            } else {
                /* general case */
                int alpha = in_alpha + MULDIV255(*outmask, 255 - in_alpha, tmp1);
                for (i = 0; i < 3; i++) {
                    /* general case */
                    *out = MULDIV255(*in, in_alpha, tmp1) +
                        MULDIV255(MULDIV255(*out, *outmask, tmp2), 255 - in_alpha, tmp3);
                    
                    *out = (*out * 255) / alpha;
                    out++, in++;
                }

                *outmask = alpha;
            }

            out++;
            if (src_has_alpha)
                in++;
            outmask += 4;
            inmask += mask_stride;
        }
    }

    return dest;
}

/* wraps alpha_over so it can be called directly from python */
/* properly refs the return value when needed: you DO need to decref the return */
PyObject *
alpha_over_wrap(PyObject *self, PyObject *args)
{
    /* raw input python variables */
    PyObject *dest, *src, *pos, *mask;
    /* destination position and size */
    int dx, dy, xsize, ysize;
    /* return value: dest image on success */
    PyObject *ret;

    if (!PyArg_ParseTuple(args, "OOOO", &dest, &src, &pos, &mask))
        return NULL;

    /* destination position read */
    if (!PyArg_ParseTuple(pos, "iiii", &dx, &dy, &xsize, &ysize)) {
        /* try again, but this time try to read a point */
        PyErr_Clear();
        xsize = 0;
        ysize = 0;
        if (!PyArg_ParseTuple(pos, "ii", &dx, &dy)) {
            PyErr_SetString(PyExc_TypeError,
                            "given blend destination rect is not valid");
            return NULL;
        }
    }

    ret = alpha_over(dest, src, mask, dx, dy, xsize, ysize);
    if (ret == dest) {
        /* Python needs us to own our return value */
        Py_INCREF(dest);
    }
    return ret;
}

/* like alpha_over, but instead of src image it takes a source color
 * also, it multiplies instead of doing an over operation
 */
PyObject *
tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg,
               unsigned char sb, unsigned char sa,
               PyObject *mask, int dx, int dy, int xsize, int ysize) {
    /* libImaging handles */
    Imaging imDest, imMask;
    /* cached blend properties */
    int mask_offset, mask_stride;
    /* source position */
    int sx, sy;
    /* iteration variables */
    unsigned int x, y;
    /* temporary calculation variables */
    int tmp1, tmp2;

    imDest = imaging_python_to_c(dest);
    imMask = imaging_python_to_c(mask);

    if (!imDest || !imMask)
        return NULL;

    /* check the various image modes, make sure they make sense */
    if (strcmp(imDest->mode, "RGBA") != 0) {
        PyErr_SetString(PyExc_ValueError,
                        "given destination image does not have mode \"RGBA\"");
        return NULL;
    }

    if (strcmp(imMask->mode, "RGBA") != 0 && strcmp(imMask->mode, "L") != 0) {
        PyErr_SetString(PyExc_ValueError,
                        "given mask image does not have mode \"RGBA\" or \"L\"");
        return NULL;
    }

    /* how far into image the first alpha byte resides */
    mask_offset = (imMask->pixelsize == 4 ? 3 : 0);
    /* how many bytes to skip to get to the next alpha byte */
    mask_stride = imMask->pixelsize;

    /* setup source & destination vars */
    setup_source_destination(imMask, imDest, &sx, &sy, &dx, &dy, &xsize, &ysize);

    /* check that there remains any blending to be done */
    if (xsize <= 0 || ysize <= 0) {
        /* nothing to do, return */
        return dest;
    }

    for (y = 0; y < ysize; y++) {
        UINT8 *out = (UINT8 *)imDest->image[dy + y] + dx * 4;
        UINT8 *inmask = (UINT8 *)imMask->image[sy + y] + sx * mask_stride + mask_offset;

        for (x = 0; x < xsize; x++) {
            /* special cases */
            if (*inmask == 255) {
                *out = MULDIV255(*out, sr, tmp1);
                out++;
                *out = MULDIV255(*out, sg, tmp1);
                out++;
                *out = MULDIV255(*out, sb, tmp1);
                out++;
                *out = MULDIV255(*out, sa, tmp1);
                out++;
            } else if (*inmask == 0) {
                /* do nothing -- source is fully transparent */
                out += 4;
            } else {
                /* general case */
                
                /* TODO work out general case */
                *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sr, *inmask, tmp1), tmp2);
                out++;
                *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sg, *inmask, tmp1), tmp2);
                out++;
                *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sb, *inmask, tmp1), tmp2);
                out++;
                *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sa, *inmask, tmp1), tmp2);
                out++;
            }

            inmask += mask_stride;
        }
    }

    return dest;
}