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J2ME in a Nutshell by Kim Topley

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Name

Graphics

Synopsis

The Graphics class provides drawing and fill operations that can be used to paint the content of a Canvas or a mutable Image. A Graphics object for a Canvas is passed to its paint() method and is valid only within that method. A Graphics object for an Image can be obtained from its getGraphics() method and remains valid as long as the Image is referenced.

All operations on a Graphics object use a coordinate reference system measured in pixels, in which the origin is initially at the top-left hand corner of the Canvas or Image. Values of the x coordinate increase when moving to the right, while y value increase downwards. The coordinate origin may be moved by calling the translate() method, supplying the coordinates of the new origin relative to the current origin. Negative coordinate values are valid and, depending on the location of the origin, may or may not correspond to points on the drawing surface. It is permissible to move the origin to a location that is outside the drawing area.

A Graphics object has an associated clipping rectangle which bounds the area within which graphics operations will be performed. The clipping rectangle for an Image is initially set to cover the entire image, while that for a Canvas is set by the platform to cover the part of the Canvas that needs to be repainted. Operations performed on a Graphics object will not change pixels that lie outside clipping rectangle, even if their scope would include those pixels. Thus, setting ...

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