FAQ

Can Davisor Chart generate GIF images?

Due to licensing issues regarding the LZH technology used in the GIF format, Davisor does not include direct support for GIF encoding.

GIF encoder support can be added with a package from Acme Laboratories. Put the package on your classpath and GIF encoding is enabled.

Alternatively, JDK versions from 1.4 and up offer a standard image encoder plugin feature that makes it possible to extended the set of supported image encoders. Unfortunately, we can not yet point out any such commercial GIF encoder plugins.

You might also want to consider moving away from the aging GIF format, and for example start using PNG instead.

Why is the image empty? (X)

Please see the server's log file for a detailed error message. An empty image is often caused due to an invalid session. Session can be initialized by shutting down browser and/or clearing browser cookies.

Why text labels within chart image are so small?

When chart image is constrained to certain size, the space available for text labels is also constrained. The text labels will always obey these constrains, even if label font size would suggest a bigger font. Furthermore, the size of related text labels is always kept consistent, so for example if the text of one of the labels is so long the text font size must be reduced in order to make the text fit in, the font size of all related labels is reduced, too.

Therefore, when increasing a font size does not seem to produce the desired visual effect, please consider making the label texts shorter, and increasing the chart image size. You may also leave the chart image size undefined, in which case the image will grow up to the minimum size neccessary to show the text labels with the full font size specified.

What does the following error message mean: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable?

The exception is thrown in Unix environments by the Java AWT toolkit when it can't make a connection to a X11 server. Davisor Chart is a graphical program that needs Java AWT services. X11 services on the other hand are often neccessary because typical AWT toolkit implementations use X11 as the principal backend graphics engine. Therefore, please make first sure that you have your local X11 environment up and running, and that the reported DISPLAY environment variable value is as expected.

If everything seems to be all right with the X11 server, check X11 authentication settings next. A quick way to get rid of any X11 authentication problems is to turn the X11 authentication mechanism off with the command 'xhost +'. If this helps, but you grow concerned about X11 security, please familiarize youself with X11 security configuration, and finetune it as neccessary.

If your host is a dedicated server without X11 support, consider installing a standard X11 environment into it. If you are reluctant to do that, please see a separate document about how to run Davisor Chart in an environment without graphic's support.

How do I get a euro symbol on a label?

You should use unicode for the label. The euro (€) symbol's code is "€". The font must support the symbol, otherwise a box will appear.

Why I get this error: SAXParseException:The entity name must immediately follow the '&' in the entity reference

Ampersand (&) is a special character in XML. Characters between ampersand (&) and semi-colon (;) form a entity reference and must either be numeric (including a # sign) or constitute a valid XML name. If you like to include ampersand in XML you must use & entity reference.
Common entity references:

&    &
<    &lt;
>    &gt;

Why taglib is found from two places, /WEB-INF/davisorchart.tld and /WEB-INF/lib/davisorchart.jar (file META-INF/taglib.tld in jar file)?

Some servers are not able to read tag libraries from jar files. For making installation as easy as possible, the taglib has been copied to a place from which all servers can read it. The web application deployment descriptor /WEB-INF/web.xml has been modified slightly so that the taglib is found from /WEB-INF directory.

Why my JVM crashes when trying to use chart 3D in Linux?

Make sure that you have the latest X 4.3.0 (or later) installed and that you are using Java3D 1.3.1-beta (or later). This is the only combination that is known to be stable. Also make sure that /etc/X11/XF86Config-4 is correct, namely that:

#       Load  "GLcore"          # OpenGL support
#       Load  "dri"             # Direct rendering infrastructure
        Load  "glx"             # OpenGL X protocol interface

...
client glx vendor string: NVIDIA Corporation
client glx version string: 1.3
...
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: GeForce4 MX 440/AGP/SSE2
OpenGL version string: 1.4.0 NVIDIA 44.96
...

You can test your installation by running glxgears and java3D demo $JAVA_HOME/demo/java3d/OffScreenCanvas3D/OffScreenTest.

If you want to run chart 3D remotely as a server, you can either use virtual Xvfb (recommended) or start X on background using screen and 'startx -- :1.0 &'. Make also sure that you set DISPLAY environment variable correctly. Finally ensure that there is enough memory available. If using Tomcat this can be done by adding 'export JAVA_OPTS=-Xmx512m' to the start script.

Why database access fails with Tomcat 4.1.27?

Make sure that you have commons-dbcp.jar and commons-pool.jar installed into your $TOMCAT/common/lib directory. Also you should have JDBC drivers (for example with mysql, mysql-connector-java-3.0.9-stable-bin.jar) installed in $TOMCAT/common/lib and $TOMCAT/webapps/chart/WEB-INF/lib directories.

If you are using JNDI, introduce the JDBC driver to the $TOMCAT/conf/server.xml similar to:

<Context path="/chart" docBase="chart" debug="0">
    <Resource name="jdbc/chart" auth="Container" type="javax.sql.DataSource"/>
    <ResourceParams name="jdbc/chart">
        <parameter>
            <name>username</name>
            <value>name</value>
        </parameter>
        <parameter>
            <name>password</name>
            <value>word</value>
        </parameter>
        <parameter>
            <name>driverClassName</name>
            <value>com.mysql.jdbc.Driver</value>
        </parameter>
        <parameter>
            <name>url</name> 
            <value>jdbc:mysql://db.davisor.com/chart</value>
        </parameter>
    </ResourceParams>
</Context>

Why 3D antialiasing does not work on my environment (charts look lo-res)?

Not all Java3D, graphics card and driver combinations support offscreen antialiasing. This is true especially on Linux.

One can try to use 'onscreen rendering' instead. This will open a window to the display into which chart is generated. Therefore, this approach is better suited when davisorchart is not run locally on a console.

Onscreen rendering can be enabled by setting the following java option:

-Ddavisor.onscreen="true"

Check also that you explicitely request antialiasing in chart XML image tag:

<image antialiasMode="on">

<image antialias="on">

Why I get 3D 'freeDisplayList(Native Method)' exceptions on Solaris?

In some Solaris configurations Java3D offscreen rendering is not stable. Adding the following switch to the java options often helps with the stability:

-Dj3d.displaylist="false"

An alternative approach is to use onscreen rendering (see above).

Why my JVM stops responding when generating 3D charts on Solaris?

On some Solaris environments with certain loads, it is possible that a deadlock occurs inside Java3D code. This can be averted by adding a java option

-Ddavisor.deadlockwait="1000"