bgcolor so you never blit your background

Author: qguv

Diff for: kernelflut.c

@@ -1,7 +1,7 @@
 #include <signal.h>	/* sigaction, sig_atomic_t */
 #include <stdbool.h>	/* bool, true, false */
 #include <stdio.h>	/* perror, printf */
-#include <stdlib.h>	/* atoi */
+#include <stdlib.h>	/* atoi, strtoul */
 #include <string.h>	/* memset */
 #include <unistd.h>	/* close, getopt */
 
@@ -32,7 +32,7 @@ static void interrupt(int _, siginfo_t *__, void *___)
 	doomed = 1;
 }
 
-static int loop(int width)
+static int loop(int width, uint32_t bgcolor)
 {
 	struct evdi_update update;
 
@@ -56,7 +56,8 @@ static int loop(int width)
 
 			err = pf_set_buf((uint32_t *) update.fb, width,
 					update.rects[rect].x1, update.rects[rect].x2,
-					update.rects[rect].y1, update.rects[rect].y2);
+					update.rects[rect].y1, update.rects[rect].y2,
+					bgcolor);
 			if (err)
 				return err;
 		}
@@ -78,6 +79,7 @@ static int usage(char *progname)
 		"\n"
 		"Options:\n"
 		"  -a			use async i/o\n"
+		"  -b RRGGBB		occasionally blit every pixel except this one\n"
 		"  -c CONNECTIONS	size of pixelflut connection pool (default %d)\n"
 		"  -d WxH		scale down to width W and height H\n"
 		"  -o X,Y		move the top-left corner down by Y pixels and right by X pixels\n"
@@ -118,13 +120,20 @@ int main(int argc, char *argv[])
 	int origin_x = 0;
 	int origin_y = 0;
 
+	uint32_t bgcolor = PF_NO_BGCOLOR;
+
 	char c;
 	int opt;
-	while ((opt = getopt(argc, argv, "ac:d:o:sph?")) != -1) {
+	while ((opt = getopt(argc, argv, "ab:c:d:o:sph?")) != -1) {
 		switch (opt) {
 		case 'a':
 			asyncio = true;
 			break;
+		case 'b':
+			bgcolor = strtoul(optarg, NULL, 16);
+			if (bgcolor > 0x00ffffff)
+				return usage(argv[0]);
+			break;
 		case 'c':
 			connections = atoi(optarg);
 			if (connections <= 0)
@@ -210,7 +219,7 @@ int main(int argc, char *argv[])
 		return err;
 
 	const int width = 800; // DEBUG
-	err = loop(width);
+	err = loop(width, bgcolor);
 	if (err == EXCEPTION_PT_FINISHED || err == EXCEPTION_INT)
 		err = 0;
 

Diff for: pixelflut.c

@@ -14,7 +14,7 @@
 
 #define ROUNDS 5
 #define STAGGER 2
-#define BYTES_PER_PIXEL 4 /* RGB32 */ // DEBUG
+#define REBLIT_FREQUENCY 23	/* should be prime and far from 2^n */
 
 /* performance test */
 #define PT_TRIALS 5
@@ -175,9 +175,12 @@ int pf_set(int x, int y, unsigned char r, unsigned char g, unsigned char b)
 	return 0;
 }
 
-int pf_set_buf(uint32_t *fb, int width, int x1, int x2, int y1, int y2)
+int pf_set_buf(const uint32_t * const fb, const int width, const int x1, const int x2, const int y1, const int y2, const uint32_t bgcolor)
 {
-	static uint32_t *last_buf = NULL;
+	static const uint32_t *last_buf = NULL;
+	static int skip_reblit = 0;
+
+	const bool ignore_bgcolor = (bgcolor == PF_NO_BGCOLOR);
 
 	if (pt_active)
 		clock_gettime(CLOCK_MONOTONIC_RAW, &pt_running);
@@ -192,15 +195,16 @@ int pf_set_buf(uint32_t *fb, int width, int x1, int x2, int y1, int y2)
 			int xi = x1 + row_bias;
 
 			for (int x = xi, i = row_start_i + xi; x < x2; x += ROUNDS, i += ROUNDS) {
+				skip_reblit = (skip_reblit + 1) % REBLIT_FREQUENCY;
 
 				/* get next connection from pool */
 				int fd = conns[active_conn_i];
 				active_conn_i = (active_conn_i + 1) % num_conns;
 
 				uint32_t color = fb[i];
 
-				/* skip redundant pixels */
-				if (last_buf && last_buf[i] == color)
+				/* skip redundant pixels. sometimes reblit anyway if skip_reblit reaches zero */
+				if (last_buf && last_buf[i] == color && (ignore_bgcolor || (color & 0x00ffffff) == bgcolor || skip_reblit))
 					continue;
 
 				/* extract colors */

Diff for: pixelflut.h

@@ -2,6 +2,8 @@
 
 #include <stdint.h>	/* uint16_t */
 
+#define PF_NO_BGCOLOR 0x80000000
+
 struct pf_size {
 	int w;
 	int h;
@@ -23,10 +25,11 @@ int pf_size(struct pf_size *ret);
 int pf_set(int x, int y, unsigned char r, unsigned char g, unsigned char b);
 
 /*
- * pf_set_buf tells pixelflut at fd to set a bunch of RGB32 pixels from fb.
- * Returns 0 on success.
+ * pf_set_buf tells pixelflut at fd to set a bunch of RGB32 pixels from fb. If
+ * bgcolor isn't PF_NO_BGCOLOR, then occasionally repaint every pixel except
+ * this color. Returns 0 on success.
  */
-int pf_set_buf(uint32_t *fb, int width, int x1, int x2, int y1, int y2);
+int pf_set_buf(const uint32_t * const fb, const int width, const int x1, const int x2, const int y1, const int y2, const uint32_t bgcolor);
 
 /*
  * pf_close closes the connection pool opened by pf_connect and deallocates its