HTML and CSS Reference
In-Depth Information
Figure 13-13: The fi nal drawing of the briefcase.
CURVES
Making curves, even with drawing tools, is trickier than drawing straight lines. To understand
how to make curves, I'll start this section with a discussion of arcs and the canvas DOM
methods for creating them. We'll look at some of the geometry, but not a lot. (You do need a
little understanding of geometry, but don't worry — it's basic.)
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h e i rst thing that you need to understand is the dif erence between degrees and radians.
Most people know that a circle has 360 degrees. On a compass rose, 360 or 0 degrees (12
o'clock) is due north. As you move clockwise to 90 degrees (3 o'clock), the compass points
east; at 180 degrees (6 o'clock), south; and at 270 degrees (9 o'clock), west.
However, you have to use radians instead of degrees, so all degrees must be converted to
×
degrees
So, let's say that you want to know the radians for due west (9 o'clock), 270 degrees:
Radians = (3.14159265 ÷ 180) = 0.01745329251994