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Linux Tutorial - The X Windowing System - Displaying Clients
  Colors ---- Fonts  


Displaying Clients

When the clients connect to the server, one key piece of information it needs is the display name. The display is of the form

hostname:displaynumber.screennumber

The hostname identifies the name of the machine to which the display is physically connected. The most common form of hostname is simply the node name, as more than likely the server is in the same network. However, it is possible to use a fully qualified domain or even an IP address for the hostname.

Unless you have some special hardware, you probably have only one physical display per server. However, each display is given a number starting at 0. If you only have one, then you will always access hostname:0. The screen number is only used in cases where a single keyboard and mouse are associated with multiple monitors. Like displays, screens are counted starting at 0. Because multiple screens are far less common than multiple displays, you can omit the screen number when specifying the display. Generally, the default display is stored in the DISPLAY variable, which is then used by default. However, many X clients have a -display option, with which you can specify the display.

The next important issue is the concept of geometry. One advantage of a system like X is the ability not only to move windows around the screen but also to change their size and shape as well. Rather than using the window manager to change the shape of the window, you can specify the shape and size when the application is started by specifying the clients geometry.

The geometry is represented by four characteristics: width, height, the distance from left or right, and the distance from the top or bottom. These are referenced by width, height, xoff, and yoff, respectively. Depending on the application, the height and width are measured in either pixels or characters, whereas the xoff and yoff values are measured only in pixels. Both xoff and yoff are measured in relationship to the screen. The general syntax of the geometry specification is

application -geometry widthxheight+xoff+yoff

Here the + (plus sign) before xoff and yoff indicate a distance from the left and top edges of the screen, respectively. By changing + to -, you change the offset to be from the right and bottom instead of left and top. For example, if you wanted to start the analog clock 30 pixels to the right of the upper left corner, the command would look like this:

oclock -geometry 90x90+30+0 &

(It's a good idea to run all clients in the background, otherwise you don't get your prompt back until the client terminates.) Now, if we wanted to start the clock 30 pixels to the left of the upper right corner, the command would look like this:

oclock -geometry 90x90-30+0 &

Now, if we wanted to start the clock 30 pixels to the left of the lower right corner, the command would look like this:

oclock -geometry 90x90-30-0 &

The four corners are thus mapped like this:

+0+0 -0+0

+0-0 -0-0

You can also specify negative offsets that would then start the client outside of the respective edge of the screen. For example, if we change the above command to look like this

oclock -geometry 90x90--30+0 &
;

It will start the client so that the right edge of the clock is 30 pixels outside of the right edge of the screen. (Be careful not to have spaces in there.) This does not mean that the entire clock is outside of the right edge of the screen. This is a misconception that many people have (including me, at first). On many systems, there is something magical about the upper left corner of the client. Offsets from the edge of the screen are in relationship to this magical corner. This is not so with X.

A +xoff value is the distance of the left edge of the client from the left edge of the screen. A -xoff value is the distance of the right edge of the client from the right edge of the screen. This also means that a +yoff value is the distance of the top of the client to the top of the screen, and -yoff is the distance from the bottom of the client to the bottom of the screen.

Note that the geometry is specified in pairs. So, if you specify the height, you must also specify the width. Also, if you specify the x-offset, you must also specify the y-offset. However, you don't have to specify the offsets if you only want to specify the size. Therefore, you could start the clock like this:

oclock -geometry 90x90 &

This gives me a 90x90 clock at the default location. If you only want the offset to take the default size, it might look like this:

oclock -geometry +100+42 &

The thing that bothers me about this clock is that it is pretty boring. The colors are drab and it really doesn't have any life to it. The nice thing is that we can change the colors. With the analog clock, we can change several different things. If we wanted the background color to be cornflower blue, we would enter the command

oclock -bg cornflowerblue &

This creates an analog clock with the default size at the default location with a background of cornflower blue. However, it still looks boring. I want a foreground of red. So, lets run the command like this:

oclock -bg cornflowerblue -fg red &

Now it's beginning to have a little life to it. However, having both hands red is still not good enough. I want the hour hand red but the minute hand white, and I want the jewel at the top of the clock yellow. The command would then look like this:

oclock -bg cornflowerblue -hour red -minute white -jewel yellow &

Thats not all. We can use a couple more options. However, these are listed in the oclock(X) man-page, so you can take a look there if you want. Other clients have different options because some of them don't make sense with an analog clock. For example, the digital clock (dclock) has an option to specify the font (-fn). Because there are no characters on the analog clock, an option to change the font wouldn't make sense.

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User Comments:


Posted by serutake on June 30, 2014 09:13am:

Very efficiently written information. http://www.friv2g.org | http://www.friv3g.com http://www.friv4g.com | http://www.friv5g.com


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