Index: sdl.c
===================================================================
RCS file: /cvsroot/qemu/qemu/sdl.c,v
retrieving revision 1.15
diff -u -3 -p -r1.15 sdl.c
--- sdl.c	5 Jul 2004 22:13:07 -0000	1.15
+++ sdl.c	10 Jul 2004 08:14:05 -0000
@@ -33,6 +33,8 @@
 #define CONFIG_SDL_GENERIC_KBD
 #endif
 
+#include <assert.h>
+
 static SDL_Surface *screen;
 static int gui_grab; /* if true, all keyboard/mouse events are grabbed */
 static int last_vm_running;
@@ -41,10 +43,126 @@ static int gui_fullscreen;
 static int gui_key_modifier_pressed;
 static int gui_keysym;
 
+/* Mechanism to reduce the total amount of data transmitted to the X
+   server, often quite dramatically.  Keep a shadow copy of video
+   memory in alt_pixels, and when asked to update a rectangle, used
+   the shadow copy to establish areas which are the same, and so do
+   not need updating.
+*/
+
+static int* alt_pixels = NULL;
+
+#define THRESH 32
+
+/* Return 1 if the area [x .. x+w-1, y .. y+w-1] is different from
+   the old version and so needs updating. */
+static int cmpArea ( int x, int y, unsigned int w, unsigned int h)
+{
+  int          i, j;
+  unsigned int sll;
+  int*         p1base = (int*)screen->pixels;
+  int*         p2base = (int*)alt_pixels;
+  assert(screen->format->BytesPerPixel == 4);
+  sll = ((unsigned int)screen->pitch) >> 2;
+
+  for (j = y; j < y+h; j++) {
+    for (i = x; i < x+w; i++) {
+      if (p1base [j * sll +i] != p2base [j * sll +i])
+	return 1;
+    }
+  }
+  return 0;
+}
+
+static void copyArea ( int x, int y, unsigned int w, unsigned int h)
+{
+  int          i, j;
+  unsigned int sll;
+  int*         p1base = (int*)screen->pixels;
+  int*         p2base = (int*)alt_pixels;
+  assert(screen->format->BytesPerPixel == 4);
+  sll = ((unsigned int)screen->pitch) >> 2;
+  for (j = y; j < y+h; j++) {
+    for (i = x; i < x+w; i++) {
+      p2base [j * sll +i] = p1base [j * sll +i];
+    }
+  }
+}
+
+
+static void econoUpdate (DisplayState *ds, int x, int y, 
+                         unsigned int w, unsigned int h)
+{
+   static int tested_total = 0;
+   static int update_total = 0;
+
+   int xi, xj, xlim, yi, yj, ylim, ntest, nupd;
+   if (w == 0 || h == 0) 
+      return;
+   xlim = x + w;
+   ylim = y + h;
+
+   ntest = nupd = 0;
+   for (xi = x; xi < xlim; xi += THRESH) {
+      xj = xi + THRESH;
+      if (xj > xlim) xj = xlim;
+      for (yi = y; yi < ylim; yi += THRESH) {
+         yj = yi + THRESH;
+         if (yj > ylim) yj = ylim;
+         if (xj-xi == 0 || yj-yi == 0)
+            continue;
+	 ntest++;
+	 if (cmpArea(xi, yi, xj-xi, yj-yi)) {
+ 	    nupd++;
+            copyArea(xi, yi, xj-xi, yj-yi);
+            SDL_UpdateRect(screen, xi, yi, xj-xi, yj-yi);
+	 }
+      }
+   }
+   tested_total += ntest;
+   update_total += nupd;
+   printf("(tested, updated):   total (%d, %d),   this time (%d, %d)\n", 
+          tested_total, update_total, ntest, nupd);
+}
+
+
 static void sdl_update(DisplayState *ds, int x, int y, int w, int h)
 {
-    //    printf("updating x=%d y=%d w=%d h=%d\n", x, y, w, h);
-    SDL_UpdateRect(screen, x, y, w, h);
+    int warned = 0;
+    //printf("updating x=%d y=%d w=%d h=%d\n", x, y, w, h);
+    //   printf("Total Size    %d %d\n", screen->w, screen->h);
+    //printf("BytesPerPixel %d\n", screen->format->BytesPerPixel);
+    //printf("pitch         %d\n", screen->pitch);
+
+    if (screen->format->BytesPerPixel != 4
+        || screen->pitch != screen->w * screen->format->BytesPerPixel) {
+       if (!warned) {
+	 warned = 1;
+	 fprintf(stderr, "qemu: SDL update optimisation disabled\n"
+                	 "      (wrong bits-per-pixel, or wrong pitch)\n");
+       }
+       SDL_UpdateRect(screen, x, y, w, h);
+       return;
+    }
+
+    assert(screen->pitch == screen->w * screen->format->BytesPerPixel);
+    assert(sizeof(int) == 4);
+    if (alt_pixels == NULL) {
+       /* First time through (at this resolution).  
+          Copy entire screen. */
+       int i, word32s = screen->w * screen->h;
+       //printf("copying init screen\n");
+       alt_pixels = malloc(word32s * sizeof(int));
+       assert(alt_pixels);
+       for (i = 0; i < word32s; i++) 
+          alt_pixels[i] = ((int*)(screen->pixels))[i];
+       SDL_UpdateRect(screen, x, y, w, h);
+       //printf("done\n");
+    } else {
+       assert(w >= 0);
+       assert(h >= 0);
+       econoUpdate(ds, x, y, w, h);
+    }
 }
 
 static void sdl_resize(DisplayState *ds, int w, int h)
@@ -53,6 +171,11 @@ static void sdl_resize(DisplayState *ds,
 
     //    printf("resizing to %d %d\n", w, h);
 
+    if (alt_pixels) {
+        free(alt_pixels);
+	alt_pixels = NULL;
+    }
+
     flags = SDL_HWSURFACE|SDL_ASYNCBLIT|SDL_HWACCEL;
     flags |= SDL_RESIZABLE;
     if (gui_fullscreen)