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Near-circular arcs generate empty paths when rounding is used #38

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jasondavies opened this issue Oct 10, 2024 · 1 comment · May be fixed by #39
Open

Near-circular arcs generate empty paths when rounding is used #38

jasondavies opened this issue Oct 10, 2024 · 1 comment · May be fixed by #39

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@jasondavies
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jasondavies commented Oct 10, 2024 •
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I encountered this edge case when using d3-shape:

d3.arc().innerRadius(55).outerRadius(75).startAngle(0).endAngle(6.283179980513967)()
"M0,-75A75,75,0,1,1,0,-75L0,-55A55,55,0,1,0,0,-55Z"

Now, d3.arc uses digits(3) by default, which means it's using d3-path with rounding.

Since there's no ambiguity when using d3-path's arc for a complete or near-circle (unlike arcTo which is undefined for coincident start/end points), and complete circular arcs are supported, I think this is a bug in d3-path, rather than d3-shape.

I traced it back to the rounding used in d3-path: nothing special is done to check for coincident points after rounding when drawing arcs.
jasondavies added a commit to jasondavies/d3-path that referenced this issue Oct 10, 2024
@jasondavies
Detect coincident points when drawing arcs with rounding.
7f4ed0d 
When rounding is used, it's possible for `arc()` to generate empty arcs
in the case where the start and end points are almost coincident, and
become coincident after rounding is applied.

This adds a check for coincident points after rounding is applied, and
splits the arc into two if coincident points are detected.

Fixes d3#38.
@jasondavies jasondavies linked a pull request Oct 10, 2024 that will close this issue
Open
jasondavies added a commit to jasondavies/d3-path that referenced this issue Oct 10, 2024
@jasondavies
Detect coincident points when drawing arcs with rounding.
97f6a50 
When rounding is used, it's possible for `arc()` to generate empty arcs
in the case where the start and end points are almost coincident, and
become coincident after rounding is applied.

This adds a check for coincident points after rounding is applied, and
splits the arc into two if coincident points are detected.

Fixes d3#38.
@jasondavies
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Arguably it's simple enough to work around by disabling rounding for d3.arc, in which case it's probably fine for d3-path to rely on the 2π angle check and generate two arc commands as it does currently. However, rounding is on by default for d3.arc.

jasondavies added a commit to jasondavies/d3-shape that referenced this issue Oct 17, 2024
@jasondavies
Add test for d3/d3-path#38 edge case.
72b06c5 
This is the edge case with endAngle close to 2π (with d3-arc's default
rounding of digits=3) that led to the fix to d3-path.
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Detect coincident points when drawing arcs with rounding. jasondavies/d3-path
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@jasondavies