kdu_region_compositor::configure_overlays

If true, overlays are enabled (or remain enabled). If false, overlays are disabled and the remaining arguments are ignored.

Specifies the minimum size occupied by the overlay's bounding box on the composited surface, at the prevailing scale. If an overlay has a bounding box which will be rendered with both dimensions smaller than min_display_size, it will not be rendered at all. Setting a modest value for this parameter, say in the range 4 to 8, helps reduce clutter when viewing an image with a lot of metadata. On the other hand, this can make it hard to locate tiny regions of significance when zoomed out to a small scale.

Parameter passed to the overridable paint_overlay function, which may be used to control the appearance of the overlay imagery. The default implementation of paint_overlay uses this parameter as follows:

• The least significant 8 bits represent a signed 2's complement number, which controls the intensity of the overlay pattern. A value of 0 represents "normal" intensity; negative values represent reduced intensity (-128 being the minimum); and positive values represent higher intensities (+127 being the maximum).
• The remaining bits are used for flashing the overlay. Each time you increment the value represented by these bits, the overlay will be modulated periodically to a different colour. The expectation is that if you want a flashing overlay, you will call the present function every half second or so.

Each time you call this function with a different value for the painting_param argument, all active metadata is scheduled for repainting with the new parameter. The actual painting occurs during calls to process — each call will repaint at most one overlay region.