PHP Cookbook

15.2. Drawing Arcs, Ellipses, and Circles

Problem

You want to draw open or filled curves. For example, you want to draw a pie chart showing the results of a user poll.

Solution

To draw an arc, use ImageArc( ):

ImageArc($image, $x, $y, $width, $height, $start, $end, $color);

To draw an ellipse, use ImageArc( ) and set $start to 0 and $end to 360:

ImageArc($image, $x, $y, $width, $height, 0, 360, $color);

To draw a circle, use ImageArc( ), set $start to 0, set $end to 360, and use the same value for both $width and $height:

ImageArc($image, $x, $y, $diameter, $diameter, 0, 360, $color);

Discussion

Because the ImageArc( ) function is highly flexible, you can easily create common curves such as ellipses and circles by passing it the right values. Like many GD functions, the first parameter is the canvas. The next two parameters are the x and y coordinates for the center position of the arc. After that comes the arc width and height. Since a circle is an arc with the same width and height, to draw a circle, set both numbers to your circle’s diameter.

The sixth and seventh parameters are the starting and ending angles, in degrees. A value of 0 is at 3 o’clock. The arc then moves clockwise, so 90 is at 6 o’clock, 180 is at 9 o’clock, and 270 is at the top of the hour. (Be careful, this behavior is not consistent among all GD functions. For example, when you rotate text, you turn in a counter-clockwise direction.) Since the arc’s center is located at ($x,$y), if you draw a semicircle from ...