Coordinate Systems - Java Tutorial 5.0 英文版

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Coordinate Systems

The Java 2D system maintains two coordinate spaces.

• User space is the space in which graphics primitives are specified.
• Device space is the coordinate system of an output device, such as a screen, window, or a printer.

User space is a device-independent logical coordinate system: the coordinate space that your program uses. All geometries passed into Java 2D rendering routines are specified in user-space coordinates.

When the default transformation from user space to device space is used, the origin of user space is the upper-left corner of the component's drawing area. The x coordinate increases to the right, and the y coordinate increases downward, as shown in the following figure.

Device space is a device-dependent coordinate system that varies according to the target rendering device. Although the coordinate system for a window or the screen might be very different from that of a printer, these differences are invisible to Java programs. The necessary conversions between user space and device space are performed automatically during rendering.

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