Poor Man's Graphics
by Keld H. Hansen
While surfing the Web you may sometimes find a site which contains a tiny
user poll. A potential question of such a poll could be, "Are you using
EJB's for Java Web applications?". Upon having answered the question (yes
or no), you're often shown the current status of the poll, and this may be
done via a small bar chart.
This chart can be made in various ways, for example by an applet, or it may
be a GIF-file constructed dynamically on the server. Another possibility is
to use 1-pixel GIF's which you simply "stretch" to have the correct width
and height. In this article I'll show how to utilize this technique. I'll
start with the HTML-basics, go through some "iterations" using JSP and
finally make a JavaBean to make the technique easy to use and give the
graphics a final touch.
When would you use this technique? Well, actually it's useful in many
situations, and it's a nice tool to have in your toolbox. Some reasons for
using it could be that the technique uses plain HTML, which allows you to
utilize style sheets, links, mouseover-effects etc. Another reason could be
that you prefer to avoid using applets to keep things as simple as
possible.
The Basics
The main idea behind using 1-pixel GIF's is that you can specify your own
width and height of any GIF-file. So to have a red, horizontal bar of
length 100 and height 10, you first create a 1 x 1 GIF-file only containing
the red color. The size is actually not important, but should be kept small
to minimize download time. You may now code:
<img src="redpixel.gif" width=100 height=10>
This will produce a bar that looks like this:
To experiment with different sizes of your GIF, you may use a simple JSP-page
like this:
<img src="redpixel.gif" width=<%=request.getParameter("w")%>
height=<%=request.getParameter("h")%>>
<form name=myform>
Width: <input type=text name=w><br>
Height: <input type=text name=h><br>
<input type=submit>
</form>
You can easily expand this example to enter the color too. I suggest that
you make a small collection of GIF's with the most common colors, and also
create the famous "invisible 1-pixel GIF" and add it to your collection. It
might be useful later on.
Keld is a web architect working for one of the largest IT-companies in Denmark.
He has more than 30 years of experience within the computer industry.
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