path2d_svgarc.md

tagline
svg-style elliptic arcs

local svgarc = require'path2d_svgarc'

Math for 2D SVG-style endpoint parametrization elliptic arcs defined as:

x1, y1, radius_x, radius_y, rotation, large_arc_flag, sweep_flag, x2, y2

where:

• (x1, y1) and (x2, y2) are the arc's endpoints
• radius_x and radius_y are the two radii of the ellipse. If negative, the absolute values are used.
• rotation is the x-axis rotation of the ellipse and defaults to 0.
• large_arc_flag is 1 if the arc should be > 180 degrees and 0 if not.
• sweep_flag is 1 for a clockwise sweep and 0 for an anticlockwise sweep.

The two flags are needed because with just the endpoints and the ellipse radii, there can be 2 possible ellipses and thus 4 possible arcs that can be represented. The flags help narrow it down to one arc.

svgarc.to_arc(x1, y1, rx, ry, rotation, large_arc_flag, sweep_flag, x2, y2, ...) ->
	cx, cy, rx, ry, start_angle, sweep_angle, rotation, ...

Convert an elliptic arc from endpoint parametrization to [center parametrization][path2d_arc].

If the endpoints conicide or rx or ry is 0, the parametrization is invalid and nothing is returned.

svgarc.split(t, x1, y1, rx, ry, rotation, large_arc_flag, sweep_flag, x2, y2) ->
	x11, y11, rx1, ry1, rotation1, large_arc_flag1, sweep_flag1, x22, y22
	x21, y21, rx2, ry2, rotation2, large_arc_flag2, sweep_flag2, x22, y22

Split a svg elliptic arc at time t into two svg arcs.

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See also: [path2d_arc]