1 files changed, 72 insertions, 0 deletions
diff --git a/.repos/farbfeld/ff2ppm.c b/.repos/farbfeld/ff2ppm.c
new file mode 100644
index 0000000..9b82d9c
--- /dev/null
+++ b/.repos/farbfeld/ff2ppm.c
@@ -0,0 +1,72 @@
+/* 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"
+#include "util.h"
+
+static void
+usage(void)
+{
+	die("usage: %s [-b colour]", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	size_t rowlen, rowoutlen;
+	uint64_t a;
+	uint32_t width, height, i, j, k, l;
+	uint16_t *row, mask[3] = { 0xffff, 0xffff, 0xffff };
+	uint8_t *rowout;
+
+	/* arguments */
+	ARGBEGIN {
+	case 'b':
+		if (parse_mask(EARGF(usage()), mask)) {
+			usage();
+		}
+		break;
+	default:
+		usage();
+	} ARGEND
+
+	if (argc) {
+		usage();
+	}
+
+	/* prepare */
+	ff_read_header(&width, &height);
+	row = ereallocarray(NULL, width, (sizeof("RGBA") - 1) * sizeof(uint16_t));
+	rowout = ereallocarray(NULL, width, (sizeof("RGB") - 1) * sizeof(uint8_t));
+	rowlen = width * (sizeof("RGBA") - 1);
+	rowoutlen = width * (sizeof("RGB") - 1);
+
+	/* write data */
+	printf("P6\n%" PRIu32 " %" PRIu32 "\n255\n", width, height);
+
+	for (i = 0; i < height; ++i) {
+		efread(row, sizeof(uint16_t), rowlen, stdin);
+
+		for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
+			a = ntohs(row[j + 3]);
+			for (l = 0; l < 3; l++) {
+				/* alpha blending and 8-bit-reduction */
+				rowout[k + l] = (a * ntohs(row[j + l]) +
+				                 (UINT16_MAX - a) * mask[l]) /
+				                (UINT16_MAX *
+						 (UINT16_MAX / UINT8_MAX));
+			}
+		}
+
+		efwrite(rowout, sizeof(uint8_t), rowoutlen, stdout);
+	}
+
+	return fshut(stdout, "<stdout>");
+}