Teach pesconvert a few command line options

diff --git a/cairo.c b/cairo.c
index 14c932a..01b4441 100644
--- a/cairo.c
+++ b/cairo.c

@@ -5,15 +5,20 @@
 #define X(stitch) ((double)((stitch)->x - pes->min_x) * outw / width)
 #define Y(stitch) ((double)((stitch)->y - pes->min_y) * outh / height)
 
-void output_cairo(struct pes *pes)
+void output_cairo(struct pes *pes, const char *filename, int size)
 {
 	int width  = pes->max_x - pes->min_x + 1;
 	int height = pes->max_y - pes->min_y + 1;
-	int outw = 256, outh = 256;
+	int outw = width, outh = height;
 	struct pes_block *block;
 	cairo_surface_t *surface;
 	cairo_t *cr;
 
+	if (size > 0) {
+		outw = size;
+		outh = size;
+	}
+
 	surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, outw, outh);
 	cr = cairo_create (surface);
 
@@ -35,5 +40,5 @@
 
 		block = block->next;
 	}
-	cairo_surface_write_to_png(surface, "out.png");
+	cairo_surface_write_to_png(surface, filename);
 }

diff --git a/main.c b/main.c
index e51401d..e9731da 100644
--- a/main.c
+++ b/main.c

@@ -23,6 +23,8 @@
 
 int main(int argc, char **argv)
 {
+	int i, outputsize = -1;
+	const char *output = NULL;
 	struct region region;
 	struct pes pes = {
 		.min_x = 65535, .max_x = -65535,
@@ -32,13 +34,43 @@
 		.listp = &pes.blocks,
 	};
 
-	if (read_path(argv[1], &region))
-		die("Unable to read file %s (%s)\n", argv[1]?argv[1]:"<stdin>", strerror(errno));
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
 
-	if (parse_pes(&region, &pes) < 0)
-		die("Unable to parse PES file\n");
+		if (*arg == '-') {
+			switch (arg[1]) {
+			case 's':
+				outputsize = atoi(argv[i+1]);
+				i++;
+				continue;
+			}
+			die("Unknown argument '%s'\n", arg);
+		}
 
-	output_cairo(&pes);
+		if (!pes.blocks) {
+			if (read_path(arg, &region))
+				die("Unable to read file %s (%s)\n", arg, strerror(errno));
+
+			if (parse_pes(&region, &pes) < 0)
+				die("Unable to parse PES file\n");
+			continue;
+		}
+
+		if (!output) {
+			output = arg;
+			continue;
+		}
+
+		die("Too many arguments (%s)\n", arg);
+	}
+
+	if (!pes.blocks)
+		die("Need an input PES file\n");
+
+	if (!output)
+		die("Need a png output file name\n");
+
+	output_cairo(&pes, output, outputsize);
 
 	return 0;
 }

diff --git a/pes.h b/pes.h
index 4656d41..1030475 100644
--- a/pes.h
+++ b/pes.h

@@ -36,6 +36,6 @@
 /* Output */
 void output_svg(struct pes *pes);
 void output_png(struct pes *pes);
-void output_cairo(struct pes *pes);
+void output_cairo(struct pes *pes, const char *filename, int size);
 
 #endif /* PES_H */