Thursday, 14 April 2011

VA Smalltalk and Seaside

I support a VA Smalltalk app for which we're adding a web interface, using Seaside. The first feature we've ported is a 'Site Map' view, a hierarchy of GIF images with configured 'hot point' rectangles for navigation. Users click to drill down to more other images or to display data in a table.

In VA the display is updated by replacing the 'image area' #labelPixmap and adjusting the window shell width and height. 'Hotpoints' are managed by mapping 'Pointer Motion' and 'Button Press' callbacks to a collection of objects that define the rectangle, which shows an action specific mouse pointer, and and triggers the action when the mouse button is pressed. All of this is user configurable using a view where they add image, draw rectangles and define actions.

A few years ago we added a feature which optionally displayed the current value of a measurement in the displayed image. It eliminated the need to click on a data 'hot point' and was handy for images with several data points. We've now added the same capability to the Seaside view.

In VA, the data is displayed by first defining instances of CwLabel in the imageArea (a WkImageWidget) at the correct position. The #labelString and #backgroundColor are then set based on user parameters, like the display date. Background color is used to show the 'quality' of value, so a grey background indicates incomplete data. To hide the data, the CwLabel's #visible property is set to false.

This is what it looks like in VA...

To do this in Seaside, we use a style 'position:absolute; left:10px; top:140px; z-index:-1;' for the GIF and then render the displayed data with...
 'position: absolute; top: %1px; left: %2px; z-index:2; border: 2px solid black; background-color: %3'
...using #bindWith:with:with: to set the top, left and background-color. The result looks like this...

I continue to be impressed with how easy it is to do interesting web work in Seaside.

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