ubb-vga.c: a bit more cleanup

- ubb-vga.c: added more section titles
- ubb-vga.c (pick, pattern): grouped pixel-generating functions with
  image generation
- ubb-vga.c (usage, main): properly parse command-line options ("getopt"
  is a bit of overkill at the moment but will be needed later)

ubb-vga/ubb-vga.c

@@ -226,7 +226,7 @@ static void until(uint16_t cycles)
 }
 
 
-/* ----- Interface --------------------------------------------------------- */
+/* ----- Frame buffer output ----------------------------------------------- */
 
 
 void setup(void)
@@ -237,18 +237,6 @@ void setup(void)
 }
 
 
-static uint32_t pick(int set, int bit, uint32_t val)
-{
-	return set == bit ? val >> 8 : 0;
-}
-
-
-static uint32_t pattern(int set, int r, int g, int b)
-{
-	return pick(set, r, R) | pick(set, g, G) | pick(set, b, B);
-}
-
-
 static void line(const uint8_t *line, const uint8_t *fetch)
 {
 	const uint8_t *p = line;
@@ -317,6 +305,21 @@ static void frame(const uint8_t *f)
 }
 
 
+/* ----- Frame buffer image generation ------------------------------------- */
+
+
+static uint32_t pick(int set, int bit, uint32_t val)
+{
+	return set == bit ? val >> 8 : 0;
+}
+
+
+static uint32_t pattern(int set, int r, int g, int b)
+{
+	return pick(set, r, R) | pick(set, g, G) | pick(set, b, B);
+}
+
+
 static void tricolor(uint32_t *f)
 {
 	int i;
@@ -377,7 +380,10 @@ static void grab(uint8_t *f)
 }
 
 
-static void session(int n)
+/* ----- Command-line parsing and main loop -------------------------------- */
+
+
+static void session(int frames)
 {
 	uint8_t f[320*(240+1)];
 	int i;
@@ -388,18 +394,45 @@ static void session(int n)
 
 	disable_interrupts();
 
-	for (i = 0; i != n; i++)
+	for (i = 0; i != frames; i++)
 		frame(f);
 
 	enable_interrupts();
 }
 
 
-int main(int argc, char **argv)
+static void usage(const char *name)
 {
-	thres = atoi(argv[2]);
+	fprintf(stderr, "usage: %s frames [threshold]\n", name);
+	exit(1);
+}
+
+
+int main(int argc, char *const *argv)
+{
+	int frames;
+	int c;
+
+	while ((c = getopt(argc, argv, "")) != EOF)
+		switch (c) {
+		default:
+			usage(*argv);
+		}
+
+	switch (argc-optind) {
+	case 2:
+		thres = atoi(argv[optind+1]);
+		/* fall through */
+	case 1:
+		frames = atoi(argv[optind]);
+		break;
+	default:
+		usage(*argv);
+	}
+
 	setup();
-	session(atoi(argv[1]));
+	session(frames);
 	cleanup();
+
 	return 0;
 }