Introduction to Pictures

A picture is an object which can be drawn to a graphics context and can be stored and restored. A picture is stored, together with its picture header, in any type of store using a storemap.

Figure 1. Relationship between picture headers and pictures in a store

A picture can thus be any object which draws an image — be it a bitmap or a set of graphic commands.

Additionally, two common desirable facilities for a picture to have are:

• the ability to be cropped

• the ability to be scaled

Scaling can be done in one of three ways:

• by specifying percentage scale factors for the width and height

• by specifying the picture size in pixels

• by specifying the picture size in twips

Cropping can be done in two ways:

• by specifying a set of margins in twips

• by specifying a further set of margins in pixels, for additional cropping

The drawing operation positions and draws the scaled and cropped picture on the graphics device.

Figure 2. The relationships between the picture classes