Layer is a simple refresh layer
Source position: layers.pas line 43
const LAYERSIMPLE = 1; |
When an application draws into the layer, any portion of the layer that is visible (not obscured) will be rendered into the common BitMap of the viewing area. All graphics rendering routines are "clipped" so that only exposed sections of the layer are drawn into. No back-up of obscured areas is provided.
If another layer operation is performed that causes an obscured part of a simple refresh layer to be exposed, the application must determine if the section need be refreshed, re-drawing the newly exposed part of the layer as required.
The basic advantage of simple refresh is that it does not require back-up area to save drawing sections that cannot be seen, saving memory. However, the application needs to monitor the layer to see if it needs refreshing. This is typically performed with statements like:
if layer^.Flags and LAYERREFRESH >< 0 then Refresh(layer);
When an application restores the layer by performing a full-layer redraw, only the damaged areas are redrawn, making the operation fairly time efficient.