1 files changed, 69 insertions, 0 deletions
diff --git a/src/blind-set-alpha.c b/src/blind-set-alpha.c
new file mode 100644
index 0000000..2e80154
--- /dev/null
+++ b/src/blind-set-alpha.c
@@ -0,0 +1,69 @@
+/* See LICENSE file for copyright and license details. */
+#include "stream.h"
+#include "util.h"
+
+#include <fcntl.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+
+USAGE("[-i] alpha-stream")
+
+static void
+process_xyza(struct stream *colour, struct stream *alpha, size_t n)
+{
+	size_t i;
+	double a;
+	for (i = 0; i < n; i += colour->pixel_size) {
+		a = ((double *)(alpha->buf + i))[1];
+		a *= ((double *)(alpha->buf + i))[3];
+		((double *)(colour->buf + i))[3] *= a;
+	}
+}
+
+static void
+process_xyza_i(struct stream *colour, struct stream *alpha, size_t n)
+{
+	size_t i;
+	double a;
+	for (i = 0; i < n; i += colour->pixel_size) {
+		a = 1 - ((double *)(alpha->buf + i))[1];
+		a *= ((double *)(alpha->buf + i))[3];
+		((double *)(colour->buf + i))[3] *= a;
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	int invert = 0;
+	struct stream colour, alpha;
+	void (*process)(struct stream *colour, struct stream *alpha, size_t n) = NULL;
+
+	ARGBEGIN {
+	case 'i':
+		invert = 1;
+		break;
+	default:
+		usage();
+	} ARGEND;
+
+	if (argc != 1)
+		usage();
+
+	colour.file = "<stdin>";
+	colour.fd = STDIN_FILENO;
+	einit_stream(&colour);
+
+	alpha.file = argv[0];
+	alpha.fd = eopen(alpha.file, O_RDONLY);
+	einit_stream(&alpha);
+
+	if (!strcmp(colour.pixfmt, "xyza"))
+		process = invert ? process_xyza_i : process_xyza;
+	else
+		eprintf("pixel format %s is not supported, try xyza\n", colour.pixfmt);
+
+	process_two_streams(&colour, &alpha, STDOUT_FILENO, "<stdout>", process);
+	return 0;
+}