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ADDING A NEW TEST MODE

The process of adding new modes to screentest is not very complicated. Follow these steps (let's assume you want to add a test called "circle").

Create the new test's source file, test_circle.c. You should copy the top of the file with copyright notice and #include statements from another source file (say test_text.c), so it looks like this:

/*
[...]
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <config.h>

#include <stdio.h>
#include <gtk/gtk.h>

#include "callbacks.h"

Add the source file name (test_circle.c) to the screentest_SOURCES variable in Makefile.am.

In test_circle.c you have to define the (non-static!) structure

G_MODULE_EXPORT struct test_ops circle_ops = {

Make sure the name of the structure ends in "_ops". This structure, which have four member functions, defines the basic operations of your test mode. The structure members are:

void circle_init(GtkWidget *widget);

This function is called when screentest is switched to your "circle" test. The argument is GtkWidget of type DrawingArea, which covers the whole screen. This function is optional, you can set it to NULL.

void circle_draw(GtkWidget *widget, gboolean clear);

This function is called when screentest decides to redraw the screen (either when mode/fgcolor/bgcolor changes, or the Expose event from the X server is received). The first argument is the same DrawingArea as above, the second one is True, when the screentest wants you to clear the window before you start drawing. This function is not optional. You must define it (after all, your test wants to draw something, doesn't it?).

void circle_cycle(GtkWidget *widget);

Screentest calls this function when user presses the left mouse button. You can use it to cycle through values of some parameter (let's say, the circle diameter). You don't need to redraw the screen. The circle_draw() function will be called afterwards. This function is optional, you can set the "cycle" member of circle_ops to NULL. The widget argument is the same as above.

void circle_close(GtkWidget *widget);

This function is called when screentest wants to switch to another mode (and is called before the new mode's init() function). You can use it to deallocate fonts, colors, timers or other resources you have allocated (for example in circle_init() function). This function is optional, you can set the "cycle" member of circle_ops to NULL. The widget argument is the same as above.

You can use the following global variables in the above functions:

GdkGC *gc, *backgc;

These are two graphic contexts. The first one has the foreground color set to the current foreground color (default white) and background color to the current background color (default black). The second one has its foreground color set to the current background color (default black) and the background color to the current foreground color (default white). So you can use the first to draw with the foreground color and the second to draw with the background color. You can (ab)use these contexts for your own colors, but remember to set the color back to its original value before your return from the circle_* function.

GdkColor fgcolors[COLOR_MAX];

The GdkColor array with preinitialized color values (see the enum test_color in callbacks.h).

GdkColor grays[GRAYS_MAX];

The GdkColor array with pixels preinitialized to the shades of gray. grays[0] is black, grays[GRAYS_MAX-1] is white. Currently the GRAYS_MAX is #defined to COLOR_MAX, but do not depend on it.

Use glade to add the new mode to the menu (alternatively, edit screentest.ui by hand). Make sure the name of the menu item is the name of your <test>_ops struct without the "_ops" ending.

Run ./autogen.sh and make.

Contributing your changes

If you want to distribute the resulting program: Beware this program is under the GNU General Public License, so if you distribute the modified version, you have to distribute the source code of all your modifications. See the file COPYING for details.

You must make the test_circle.c available, but you don't have to send it to the author of this program. However, the author of this program kindly asks you to contribute any modifications. Please send your modifications to the author of screentest, Tobias Gruetzmacher [email protected]. The preferred form of the contribution is either a GitHub pull request or an unified diff. To make a unified diff, follow these steps:

  • rename your directory with modified sources (for example mv screentest-2.0 screentest-2.0-circle).
  • run make distclean in this directory.
  • unpack the clean sources again: zcat screentest-2.0.tar.gz | tar xvf -
  • create the patch with the following command: diff -uNr screentest-2.0 screentest-2.0-circle > screentest-circle.patch
  • mail the screentest-circle.patch to the author.

Thanks,