Source: https://build.opensuse.org/source/home:Akoellh/xzoom/xzoom-0.3.shm.diff?rev=68bf54e9d06f0bce019d310ccd70d579
Date: 2021-02-16
diff -uraN xzoom-0.3.orig/xzoom.c xzoom-0.3/xzoom.c
--- xzoom-0.3.orig/xzoom.c	2017-10-12 17:53:38.446984725 +0200
+++ xzoom-0.3/xzoom.c	2017-10-12 17:54:46.094982727 +0200
@@ -28,6 +28,8 @@
                           some other minor changes/fixes
 tony mancill		2002/02/13 <tmancill@debian.org>       
 			hacked in support for WM_DELETE_WINDOW
+Egmont Koblinger          Added XSHM auto detection,
+                          -shm, -noshm and -autoshm option
 */
 
 #include <stdio.h>
@@ -87,6 +89,9 @@
 #define MAGX	MAG				/* horizontal magnification */
 #define MAGY	MAG				/* vertical magnification */
 
+int use_xshm = 1;
+int force_xshm = 0;
+
 int xgrab, ygrab;				/* where do we take the picture from */
 
 int magx = MAGX;
@@ -136,7 +141,7 @@
 
 	for(i = 0; i < 2; i++) {
 
-#ifdef XSHM
+if (use_xshm) { /*#ifdef XSHM*/
 		ximage[i] = XShmCreateImage(dpy,
 			DefaultVisualOfScreen(scr),
 			DefaultDepthOfScreen(scr),
@@ -172,11 +177,15 @@
 		ximage[i]->data = shminfo[i].shmaddr;
 		shminfo[i].readOnly = False;
 
-		XShmAttach(dpy, &shminfo[i]);
-		XSync(dpy, False);
+		if (XShmAttach(dpy, &shminfo[i]) || force_xshm) {
+			XSync(dpy, False);
 
-		shmctl(shminfo[i].shmid, IPC_RMID, 0);
-#else
+			shmctl(shminfo[i].shmid, IPC_RMID, 0);
+		} else {
+			use_xshm = 0;
+		}
+}
+if (!use_xshm) { /*#else*/
 		char *data;
 		data = malloc(BitmapUnit(dpy) / 8 * width[i] * height[i]);
 
@@ -191,7 +200,7 @@
 			exit(-1);
 		}
 
-#endif /* XSHM */
+} /*#endif*/ /* XSHM */
 	}
 	created_images = True;
 }
@@ -204,12 +213,12 @@
 		return;
 
 	for(i = 0; i < 2; i++) {
-#ifdef XSHM
+if (use_xshm) { /*#ifdef XSHM*/
 		XShmDetach(dpy, &shminfo[i]);	/* ask X11 to detach shared segment */
 		shmdt(shminfo[i].shmaddr);		/* detach it ourselves */
-#else
+} else { /*#else*/
 		free(ximage[i]->data);
-#endif
+} /*#endif*/
 		ximage[i]->data = NULL;			/* remove refrence to that address */
 		XDestroyImage(ximage[i]);		/* and destroy image */
 	}
@@ -222,6 +231,9 @@
 	fprintf(stderr, "Usage: %s [ args ]\n"
 		"Command line args:\n"
 		"-display displayname\n"
+		"-shm\n"
+		"-noshm\n"
+		"-autoshm\n"
 		"-mag magnification [ magnification ]\n"
 		"-geometry geometry\n"
 		"-source geometry\n"
@@ -351,6 +363,22 @@
 			continue;
 		}
 
+		if(!strcmp(argv[0], "-shm")) {
+			force_xshm = 1;
+			use_xshm = 1;
+			continue;
+		}
+		if(!strcmp(argv[0], "-noshm")) {
+			force_xshm = 0;
+			use_xshm = 0;
+			continue;
+		}
+		if(!strcmp(argv[0], "-autoshm")) {
+			force_xshm = 0;
+			use_xshm = 1;
+			continue;
+		}
+
 		if(!strcmp(argv[0], "-mag")) {
 			++argv; --argc;
 
@@ -818,14 +846,14 @@
 
 		}
 
-#ifdef XSHM
+if (use_xshm) { /*#ifdef XSHM*/
 		XShmGetImage(dpy, RootWindowOfScreen(scr), ximage[SRC],
 			xgrab, ygrab, AllPlanes);
-#else
+} else { /*#else*/
 		XGetSubImage(dpy, RootWindowOfScreen(scr),
 			xgrab, ygrab, width[SRC], height[SRC], AllPlanes,
 			ZPixmap, ximage[SRC], 0, 0);
-#endif
+} /*#endif*/
 #ifdef FRAME
 		if(buttonpressed) {	/* show the frame */
 			DRAW_FRAME();
@@ -840,11 +868,11 @@
 		else if (depth <= 8*sizeof(int))
 			scale32();
 
-#ifdef XSHM
+if (use_xshm) { /*#ifdef XSHM*/
 		XShmPutImage(dpy, win, gc, ximage[DST], 0, 0, 0, 0, width[DST], height[DST], False);
-#else
+} else { /*#else*/
 		XPutImage(dpy, win, gc, ximage[DST], 0, 0, 0, 0, width[DST], height[DST]);
-#endif
+} /*#endif*/
 		if(set_title) {
 			if(magx == magy && !flipx && !flipy && !flipxy)
 				sprintf(title, "%s x%d", progname, magx);
diff -uraN xzoom-0.3.orig/xzoom.man xzoom-0.3/xzoom.man
--- xzoom-0.3.orig/xzoom.man	2017-10-12 17:53:38.446984725 +0200
+++ xzoom-0.3/xzoom.man	2017-10-12 17:56:39.442979378 +0200
@@ -9,6 +9,7 @@
 [ \-display \fIdisplayname\fP ] [ \-mag \fImag\fP [ \fImag\fP ] ]
 [ \-x ] [ \-y ] [ \-xy ]
 [ \-geometry \fIgeometry\fP ] [ \-source \fIgeometry\fP ]
+[ \-shm ] [ \-noshm ] [ \-autoshm ]
 .SH OPTIONS
 .LP
 .TP 5
@@ -38,6 +39,16 @@
 The dimensions of this area are multiplied by the magnification to
 get the size of \fBxzoom\fR's window. If these dimensions are given
 separately (by use of \-geometry ) then an error is reported.
+.TP 5
+.B \-shm
+Force XSHM extension.
+.TP 5
+.B \-noshm
+Disable XSHM extension.
+.TP 5
+.B \-autoshm
+Try to autodetect if XSHM is available. This is the default. Unfortunately
+this is not perfect, sometimes you need to manually give \-noshm.
 .br
 .SH DESCRIPTION
 .IR Xzoom
@@ -148,6 +159,7 @@
 For best performance the shared memory extension for X11 is
 used. Xzoom will fail if it is compiled to use XSHM and its
 display is not on the local host.
+However, Auto detection of XSHM is far from perfect.
 .LP 5
 \(dg
 Xzoom is given with no warranty. It was tested only under