ubb-vga: option -d to double the number of set/clear pairs, improving resolution

- README: added compatibility of double mode
- ubb-vga.c (usage, main): new option -d to double the number of set/clear
  pairs (making lines longer and the apparent pixel clock slower)
- ubb-vga.c (grab, session, main): have a complete set/clear pair for each
  pixel in double mode

ubb-vga/README

@@ -43,11 +43,18 @@ don't mind.
 Compatibility
 -------------
 
-ubb-vga has been tested with the following monitors:
+ubb-vga in single mode has been tested with the following monitors:
 
-Display			Size		Quality
+Display			Monitor size	Quality
 -----------------------	---------------	----------------------------------
 Xenon XEN-1510T		15", 1024x768	good
 Samsung 206NW		20", 1680x1050	poor (horizontal instability)
 LG W2243C		22", 1920x1080	acceptable (slight instability)
 LG W2243L		22", 1920x1080	acceptable (slight instability)
+
+In double mode:
+
+Display			Pixels missing	Quality
+			left/right
+-----------------------	---------------	------------------
+Xenon XEN-1510T		5 / 25		good

ubb-vga/ubb-vga.c

@@ -229,7 +229,7 @@ static void until(uint16_t cycles)
 /* ----- Frame buffer output ----------------------------------------------- */
 
 
-static int line_pairs = 160;	/* set/unset pairs */
+static int line_pairs = 160;	/* set/clear pairs */
 static int line_cycles = US(36); /* nominally 31.77 us, but we're too slow  */
 
 
@@ -366,19 +366,28 @@ static void grid(uint8_t *f)
 }
 
 
-static void grab(uint8_t *f)
+static void grab(uint8_t *f, int single)
 {
 	uint32_t *fb = map(0x01d00000, 4*320*240);
 	int x, y;
 	uint32_t pix;
+	uint8_t r, g, b;
 
 	for (y = 0; y != 240; y++)
 		for (x = 0; x != 320; x++) {
 			pix = *fb++;
+			r = pix >> 16;
+			g = pix >> 8;
+			b = pix;
+			if (single)
 				*f++ = pattern(!(x & 1),
-			    ((pix >> 16) & 255) >= thres,
+				    r >= thres, g >= thres, b >= thres);
-			    ((pix >> 8) & 255) >= thres,
+			else {
-			    (pix & 255) >= thres);
+				*f++ = pattern(1,
+				    r >= thres, g >= thres, b >= thres);
+				*f++ = pattern(0,
+				    r >= thres, g >= thres, b >= thres);
+			}
 		}
 }
 
@@ -386,13 +395,13 @@ static void grab(uint8_t *f)
 /* ----- Command-line parsing and main loop -------------------------------- */
 
 
-static void session(int frames)
+static void session(int frames, int single)
 {
 	uint8_t f[2*line_pairs*(240+1)];
 	int i;
 
 	memset(f, 0, sizeof(f));
-	grab(f);
+	grab(f, single);
 //	grid(f);
 
 	disable_interrupts();
@@ -406,7 +415,12 @@ static void session(int frames)
 
 static void usage(const char *name)
 {
-	fprintf(stderr, "usage: %s frames [threshold]\n", name);
+	fprintf(stderr,
+"usage: %s frames -d [threshold]\n\n"
+"  frames     number of frames to display\n"
+"  threshold  channel on/off threshold\n\n"
+"  -d  double the number of set/clear pairs\n"
+    , name);
 	exit(1);
 }
 
@@ -414,10 +428,16 @@ static void usage(const char *name)
 int main(int argc, char *const *argv)
 {
 	int frames;
+	int single = 1;
 	int c;
 
-	while ((c = getopt(argc, argv, "")) != EOF)
+	while ((c = getopt(argc, argv, "d")) != EOF)
 		switch (c) {
+		case 'd':
+			single = 0;
+			line_pairs = 320;
+			line_cycles = US(36+26);
+			break;
 		default:
 			usage(*argv);
 		}
@@ -434,7 +454,7 @@ int main(int argc, char *const *argv)
 	}
 
 	setup();
-	session(frames);
+	session(frames, single);
 	cleanup();
 
 	return 0;