UXEdge

UXEdge is a single line segment: two endpoints, and nothing else.

#use <UXKit>            // or #import "UXShapePath.xc"

Overview

class UXEdge : Object {
    i16 x0; i16 y0;
    i16 x1; i16 y1;
}

UXShapePath.edges produces them. Edges reduce the path to the form that geometry code handles most easily: segments only, with no curves, no subpath structure and no current point.

Why a separate type from UXPathElement

They describe the same shape at different stages.


`UXPathElement`	what the author drew: commands, curves, and an implicit current point
`UXEdge`	what the geometry runs on: explicit, self-contained segments

An element depends on the one before it; an edge does not. Because each edge carries both of its endpoints, a containment test can look at edges in any order, and a scanline filler can sort them.

Every subpath arrives closed

edges() closes each subpath as it emits it, whether or not you called close. The edge list therefore always describes closed regions. Even-odd containment depends on this, since an open outline has no inside.

As a result, an unclosed triangle still hit-tests as a triangle, and its edge count is three, not two.

Zero-length edges are dropped

Consecutive identical points produce no edge. A degenerate segment has no direction, and a containment test that counted it would either double-count a crossing or divide by zero computing one.

An edge from edges() is always a real segment with (x0,y0) != (x1,y1), and the count can be lower than the number of lineTo calls that produced it.

Direction is preserved, and unused

An edge runs from 0 to 1 in the order the path was drawn. Even-odd containment counts crossings, not windings, so the direction has no meaning for the tests here.

Direction matters if you add a non-zero winding rule of your own, which needs to know which way each edge crosses the ray. The information is kept for that purpose; nothing in the toolkit reads it.

Fields

x0 / y0

i16 x0; i16 y0

The start point.

x1 / y1

i16 x1; i16 y1

The end point.

Example

triangle:  x=10 y=10 w=80 h=70 edges=3
unclosed:  x=10 y=10 w=80 h=70 edges=3
blob:      x=20 y=20 w=60 h=60 edges=70
ring:      x=0 y=0 w=100 h=100 edges=8
empty:     x=0 y=0 w=0 h=0 edges=0

The closed and unclosed triangles give the same three edges. The two-subpath ring gives eight. A curved blob gives seventy, the flattener’s result at a quarter-pixel tolerance.

The program is website/site/examples/uxkit/shapes.xc; the doc-examples gate compiles it, and the output above is what it prints.

Conforms to

Inherits Object