Graphics

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Graphics



aUCBLogo provides traditional Logo turtle graphics with one or more turtles. Collision detection is not supported. This is the most hardware-dependent part of Logo; some features may exist on some machines but not others. Nevertheless, the goal has been to make Logo programs as portable as possible, rather than to take fullest advantage of the capabilities of each machine. In particular, Logo attempts to scale the screen so that turtle coordinates [-400 -300] and [400 300] fit on the graphics window, and so that the aspect ratio is 1:1, although some PC screens have nonstandard aspect ratios.

The center of the graphics window (which may or may not be the entire screen, depending on the machine used) is turtle location [0 0]. Positive X is to the right; positive Y is up. Headings (angles) are measured in degrees clockwise from the positive Y axis. (This differs from the common mathematical convention of measuring angles counterclockwise from the positive X axis.) The turtle is represented as an isoceles triangle; the actual turtle position is at the midpoint of the base (the short side).

Colors are, of course, hardware-dependent. However, Logo provides partial hardware independence by interpreting color numbers 0 through 7 uniformly on all computers: 

0  black         1  blue             2  green           3  cyan
4  red            5  magenta       6  yellow         7  white

Where possible, Logo provides additional user-settable colors; how many are available depends on the hardware and operating system environment. If at least 16 colors are available, Logo tries to provide uniform initial settings for the colors 8-15: 

 8  brown        9  tan            10  forest         11  aqua
12  salmon    13  purple        14  orange       15  grey

Logo begins with a white background and black pen.

Graphics

Example:

References:

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