Reference for unit 'layers'

Layer handling

Overview

provides routines that are used to manage overlapping rectangular drawing areas that share a common display. Intuition uses the layers library to manage its system of windows.

The concept of a layer is closely tied to Intuition windows. A layer is a rectangular drawing area. A layer can overlap other layers and has a display priority that determines whether it will appear in front or behind other layers. Every Intuition window has an associated Layer structure. Layers allow Intuition and application programs to :

• Share a display's BitMap among various tasks in an orderly way by creating layers, separate drawing rectangles, within the BitMap.
• Move, size or depth-arrange a layer while automatically keeping track of which portions of other layers are hidden or revealed by the operation.
• Manage the remapping of coordinates, so the application need not track the layer's offset into the BitMap.
• Maintain each layer as a separate entity, which may optionally have its own BitMap.
• Automatically update same newly visible portions.

The layers library takes care of housekeeping: the low level, repetitive tasks which are required to keep track of where to place bits. The layers library also provides a locking mechanism which coordinates display updating when multiple tasks are drawing graphics to layers. The windowing environment provided by the Intuition library is largely based on layers.

Warning

Layers may not be created or used directly with Intuition screens. Intuition windows are the only supported method of adding layers to Intuition screens. Only the layer locking and unlocking functions are safe to use with Intuition. An application must create and manage its own View if it will be creating layers directly on the display.