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This program is an example of using timer events to do a task in the background while allowing the the user interface to still respond to events. This technique requires the background task to be split into parts which are short enough for each part to complete quickly enough for a user to not notice a delay if he begins to interact with the interface. In other words, if each part of the task takes 0.1 seconds, then there is a potential delay of 0.1 seconds before the user interface will respond.

Here are the source and docs for the demo.

Continue reading “Timer events to process a task in the background.”

A couple weeks ago, I wrote a demo program to view JPEG 2000 images as a “regular” widget program. Now I want to rewrite the same program as an “object widget,” in other words write methods of a class instead of normal functions and procedures. You need to already understand the basics of object-oriented and widget programming in IDL to follow along with this example. The following files are needed for this program: mgtilejp2__define.pro (doc), mgobjectwidget__define.pro (doc), mg_object_event_handler.pro (doc), and mg_object_cleanup.pro (doc).

Continue reading “Object widgets.”

IDL 6.2 added several new capabilities to the IDLgrImage class in the object graphics system. One of them is the ability to support large images using tiling. (Another is significantly faster rendering time in typical cases.)

The new tiling features allow portions of the image to be read from a data source as needed. For applications that zoom using data sources with an image pyramid, level of detail rendering is used. For example, if a thumbnail of the entire image is needed, only a low resolution image is requested from the data source and rendered by IDLgrImage.

The mechanics of how this works requires a bit of communication between the destination object (IDLgrWindow, IDLgrBuffer, IDLgrClipboard or IDLgrPrinter support it) and the IDLgrImage object using a few new methods (most notably, queryRequiredTiles for the destination objects and setTileData for IDLgrImage).

Running the demo

The demo program is a minimal tiling image viewer which supports scrolling (click and drag as well as with the arrow keys) and zooming (page up and page down). To test it out:

1. First download the source code (mg_tilejp2.pro and mg_tilejp2_demo.pro).
2. Change directories in IDL to a directory that you want to save the JPEG 2000 data file in.
3. You need to run mg_tilejp2_demo at least the first time you run the demo code in order for the JPEG2000 image to be created. After that, you can run mg_tilejp2 directly.

Continue reading “IDLgrImage tiling in IDL 6.2.”