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: 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: The relationships between the picture classes