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	ff2ppm.c - farbfeld - suckless image format with conversion tools
	git clone git://git.suckless.org/farbfeld
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	ff2ppm.c (1526B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include <arpa/inet.h>
	3
	4 #include <errno.h>
	5 #include <inttypes.h>
	6 #include <stdint.h>
	7 #include <stdio.h>
	8 #include <stdlib.h>
	9 #include <string.h>
	10
	11 #include "arg.h"
	12 #include "util.h"
	13
	14 static void
	15 usage(void)
	16 {
	17 die("usage: %s [-b colour]", argv0);
	18 }
	19
	20 int
	21 main(int argc, char *argv[])
	22 {
	23 size_t rowlen, rowoutlen;
	24 uint64_t a;
	25 uint32_t width, height, i, j, k, l;
	26 uint16_t *row, mask[3] = { 0xffff, 0xffff, 0xffff };
	27 uint8_t *rowout;
	28
	29 /* arguments */
	30 ARGBEGIN {
	31 case 'b':
	32 if (parse_mask(EARGF(usage()), mask)) {
	33 usage();
	34 }
	35 break;
	36 default:
	37 usage();
	38 } ARGEND
	39
	40 if (argc) {
	41 usage();
	42 }
	43
	44 /* prepare */
	45 ff_read_header(&width, &height);
	46 row = ereallocarray(NULL, width, (sizeof("RGBA") - 1) * sizeof(u…
	47 rowout = ereallocarray(NULL, width, (sizeof("RGB") - 1) * sizeof…
	48 rowlen = width * (sizeof("RGBA") - 1);
	49 rowoutlen = width * (sizeof("RGB") - 1);
	50
	51 /* write data */
	52 printf("P6\n%" PRIu32 " %" PRIu32 "\n255\n", width, height);
	53
	54 for (i = 0; i < height; ++i) {
	55 efread(row, sizeof(uint16_t), rowlen, stdin);
	56
	57 for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
	58 a = ntohs(row[j + 3]);
	59 for (l = 0; l < 3; l++) {
	60 /* alpha blending and 8-bit-reduction */
	61 rowout[k + l] = (a * ntohs(row[j + l]) +
	62 (UINT16_MAX - a) * mask…
	63 (UINT16_MAX *
	64 (UINT16_MAX / UINT8_MAX…
	65 }
	66 }
	67
	68 efwrite(rowout, sizeof(uint8_t), rowoutlen, stdout);
	69 }
	70
	71 return fshut(stdout, "<stdout>");
	72 }