xzoom - magnify part of the screen, with fast updates

xzoom [ -display displayname ] [ -mag mag [ mag ] ] [ -x ] [ -y ] [ -xy ] [ -geometry geometry ] [ -source geometry ]

-display displayname | -d displayname

The name of the display to use (not very useful).

-mag mag [ mag ]

What magnification to use. If two number arguments are supplied the first is used for X magnifications and the second is used for Y magnification. Magnification should be greater than 0.

-x

Mirror horizontally.

-y

Mirror vertically.

-xy | -z

Exchange X and Y axes before any magnification is performed.

-geometry geometry | =geometry

Size and position xzoom's window.

-source geometry

Size and position the initial source area which is magnified. The dimensions of this area are multiplied by the magnification to get the size of xzoom's window. If these dimensions are given separately (by use of -geometry ) then an error is reported.

Xzoom displays in its window a magnified area of the X11 display. The user can interactively change the zoomed area, the window size, magnification (optionally different magnification for X and Y axes) or rotate or mirror the image.

Once xzoom has started the user can enter simple commands using the keyboard.

q

quit.

+

increase magnification value by 1.

-

decrease magnification value by 1.

w

next + or - command only affect X magnification.

h

next + or - command only affect Y magnification.

x

mirror the display image horizontally.

y

mirror the display image vertically.

z

rotate the displayed image 90 degrees counter-clockwise.

arrow keys

scroll the zoomed area 1 pixel in the direction of the arrow. if the control key is pressed the zoomed area will scroll 10 pixels.

d

sets the delay between frame updates. Built-in delays are 200, 100, 50, 10 and 0 ms.

g

toggle grid on and off.

Mouse buttons

To set the location of the magnified are click the left mouse button inside xzoom's window and then move it (keep the button pressed) to the place which you want to see magnified. Xzoom allow you to resize it's window at any time. When xzoom is iconified it simply waits to get deiconified.

Xzoom uses the window's title bar to inform the user about it's status. Normally the title says something like xzoom x2 which means the magnification is 2 both in X and Y axes. If the image is stretched differently on the X and Y axes the title will say xzoom X 2; Y 4. Negative numbers mean reflection. If the image is rotated by 90 or 270 degrees the title will show <=> between the X and Y values. When d is depressed the title will display the new delay value for approximately 2 seconds and then revert to the default display of magnification values.

Xzoom is fast enough to display enlarged or mirrored animations in small windows. On my 486 DX2-66 and Cirrus Logic CL-GD5428 display card (attached to Vesa local bus) update of a 256x256 window magnified by 2 (ie, source rect is 128x128) takes approximately 30 ms. This time varies, off course when a different size window or different magnification is used. If we chose 50 ms between updates we can get about 12.5 frames per second and still let an animation program do it's work. It is possible to compile xzoom without X shared memory support. In that case window update may be about 3 times slower (if we are using a local display, using LAN is a different story).

xmag.1x.

I got the motivation for writing xzoom after I saw a similar WindowsNT program, zoomin working. It started just as a test for X11 performance. I don't have the fancy menus and scrollbar like zoomin but I do have all their features (and more) accessible from the keyboard.

The maximum internal built in delay (see command d above) was set to 200 ms. Xzoom completes the delay before polling the X event queue for the next command. Larger delays would feel like poor response to user commands.

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.

Xzoom is given with no warranty. It was tested only under Linux with Xfree86 release 3.1.2 (X11R6).

Some strange behavior may occur if the requested magnified area falls beyond the borders of the screen. Example is when you have magnification of 1 and a window whose width is greater than the height of the screen and you want 90 degrees rotation. In that case part of the window will not get updated.

The frame used to mark the zoomed area may corrupt the contents of other windows if they are modified when the frame is visible. If you don't like it disable the -DFRAME option when compiling xzoom.

Itai Nahshon