Practical Programming in Tcl & Tk, Third Edition

The Min Max Scale Example

This section presents Example 34-3 that constructs a scale-like object with two sliders. The sliders represent the minimum and maximum values for some parameter. Clearly, the minimum cannot be greater than the maximum, and vice versa. The example creates three rectangles on the canvas. One rectangle forms the long axis of the slider that represents the range of possible values. The other two rectangles are markers that represent the values. Two text objects float below the markers to give the current values of the minimum and maximum.

The example introduces four canvas operations: bbox, coords, scale, and move. The bbox operation returns the bounding box of an object or of all objects with a given tag. The coords operation ...