pngdriver/draw_bitmap.c

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/*!
   \file lib/pngdriver/draw_bitmap.c
 
   \brief GRASS png display driver - draw bitmap
 
   (C) 2003-2014 by Per Henrik Johansen and the GRASS Development Team
 
   This program is free software under the GNU General Public License
   (>=v2). Read the file COPYING that comes with GRASS for details.
 
   \author Per Henrik Johansen (original contributor)
   \author Glynn Clements
 */
 
#include <math.h>
#include "pngdriver.h"
 
#ifndef min
#define min(a, b) ((a) < (b) ? (a) : (b))
#endif
#ifndef max
#define max(a, b) ((a) > (b) ? (a) : (b))
#endif
 
/*!
   \brief Draw bitmap
 
   \param ncols,nrows number of columns and rows
   \param threshold threshold value
   \param buf data buffer
 */
void PNG_draw_bitmap(int ncols, int nrows, int threshold,
                     const unsigned char *buf)
{
    int i0 = max(png.clip_left - cur_x, 0);
    int i1 = min(png.clip_rite - cur_x, ncols);
    int j0 = max(png.clip_top - cur_y, 0);
    int j1 = min(png.clip_bot - cur_y, nrows);
 
    if (!png.true_color) {
        int i, j;
 
        for (j = j0; j < j1; j++) {
            int y = cur_y + j;
 
            for (i = i0; i < i1; i++) {
                int x = cur_x + i;
                unsigned int k = buf[j * ncols + i];
                unsigned int *p = &png.grid[y * png.width + x];
 
                if (k > (unsigned int)threshold)
                    *p = png.current_color;
            }
        }
    }
    else {
        int r1, g1, b1, a1;
        int i, j;
 
        png_get_pixel(png.current_color, &r1, &g1, &b1, &a1);
 
        for (j = j0; j < j1; j++) {
            int y = cur_y + j;
 
            for (i = i0; i < i1; i++) {
                int x = cur_x + i;
                unsigned int k = buf[j * ncols + i];
                unsigned int *p = &png.grid[y * png.width + x];
                int a0, r0, g0, b0;
                unsigned int a, r, g, b;
 
                png_get_pixel(*p, &r0, &g0, &b0, &a0);
 
                a = (a0 * (255 - k) + a1 * k) / 255;
                r = (r0 * (255 - k) + r1 * k) / 255;
                g = (g0 * (255 - k) + g1 * k) / 255;
                b = (b0 * (255 - k) + b1 * k) / 255;
 
                *p = png_get_color(r, g, b, a);
            }
        }
    }
 
    png.modified = 1;
}