add ff2ppm(1)

ff2ppm can convert farbfeld images to PPM (P6 binary format, 24-bit RGB).
ff2ppm has an option -b to set the background color, for example for png files:

png2ff < test.png | ff2ppm -b '#00ff00' > test.ppm

1 files changed, 125 insertions, 0 deletions

diff --git a/ff2ppm.c b/ff2ppm.c
new file mode 100644
index 0000000..7f6aa61
--- /dev/null
+++ b/ff2ppm.c
@@ -0,0 +1,125 @@
+/* See LICENSE file for copyright and license details. */
+#include <arpa/inet.h>
+
+#include <errno.h>
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "arg.h"
+
+char *argv0;
+
+static void
+usage(void)
+{
+	fprintf(stderr, "usage: %s [-b #rrggbb]\n", argv0);
+	exit(1);
+}
+
+int
+main(int argc, char *argv[])
+{
+	size_t rowlen;
+	uint32_t hdr[4], width, height, i, j, k;
+	uint16_t *row, mr = 0xffff, mg = 0xffff, mb = 0xffff;
+	uint8_t *rowout;
+	char *color;
+	unsigned int r = 0xff, g = 0xff, b = 0xff;
+	float a;
+
+	argv0 = argv[0];
+	ARGBEGIN {
+	case 'b':
+		for (color = EARGF(usage()); *color && *color == '#'; color++)
+			;
+
+		switch (strlen(color)) {
+		case 3:
+			if (sscanf(color, "%1x%1x%1x", &r, &g, &b) != 3)
+				usage();
+			mr = (r | r << 4) * 257;
+			mg = (g | g << 4) * 257;
+			mb = (b | b << 4) * 257;
+			break;
+		case 6:
+			if (sscanf(color, "%2x%2x%2x", &r, &g, &b) != 3)
+				usage();
+			mr = r * 257;
+			mg = g * 257;
+			mb = b * 257;
+			break;
+		case 12:
+			if (sscanf(color, "%4x%4x%4x", &r, &g, &b) != 3)
+				usage();
+			mr = r;
+			mg = g;
+			mb = b;
+			break;
+		default:
+			usage();
+		}
+		break;
+	default:
+		usage();
+	} ARGEND
+
+	if (argc)
+		usage();
+
+	/* header */
+	if (fread(hdr, sizeof(*hdr), 4, stdin) != 4) {
+		fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
+		return 1;
+	}
+	if (memcmp("farbfeld", hdr, sizeof("farbfeld") - 1)) {
+		fprintf(stderr, "%s: invalid magic value\n", argv0);
+		return 1;
+	}
+	if (!(width = ntohl(hdr[2]))) {
+		fprintf(stderr, "%s: invalid width: zero\n", argv0);
+		return 1;
+	}
+	if (!(height = ntohl(hdr[3]))) {
+		fprintf(stderr, "%s: invalid height: zero\n", argv0);
+		return 1;
+	}
+	if (width > SIZE_MAX / ((sizeof("RGBA") - 1) * sizeof(uint16_t))) {
+		fprintf(stderr, "%s: row length integer overflow\n", argv0);
+		return 1;
+	}
+
+	rowlen = width * (sizeof("RGBA") - 1);
+	if (!(row = malloc(rowlen * sizeof(uint16_t)))) {
+		fprintf(stderr, "%s: malloc: %s\n", argv0, strerror(errno));
+		return 1;
+	}
+	if (!(rowout = malloc(width * sizeof("RGB") - 1))) {
+		fprintf(stderr, "%s: malloc: %s\n", argv0, strerror(errno));
+		return 1;
+	}
+
+	/* PPM binary */
+	printf("P6\n%" PRIu32 " %" PRIu32 "\n255\n", width, height);
+
+	/* write rows */
+	for (i = 0; i < height; ++i) {
+		if (fread(row, sizeof(uint16_t), rowlen, stdin) != rowlen) {
+			fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
+			return 1;
+		}
+		for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
+			a = ntohs(row[j + 3]) / 65535.0f;
+			rowout[k]     = ((ntohs(row[j]) * a)     + (mr * (1 - a))) / 257;
+			rowout[k + 1] = ((ntohs(row[j + 1]) * a) + (mg * (1 - a))) / 257;
+			rowout[k + 2] = ((ntohs(row[j + 2]) * a) + (mb * (1 - a))) / 257;
+		}
+		if (fwrite(rowout, 3, width, stdout) != width) {
+			fprintf(stderr, "%s: fwrite: %s\n", argv0, strerror(errno));
+			return 1;
+		}
+	}
+	return 0;
+}