Closed Bug 1278512 Opened 4 years ago Closed 4 years ago

The path flattening code doesn't generate any vertex in some cases (inflection points at 1.0 or 0.0)


(Core :: Graphics, defect)

Not set



Tracking Status
firefox50 --- fixed


(Reporter: nical, Assigned: nical)



(Whiteboard: [gfx-noted])


(1 file)

FlattenBezier in Path.cpp starts by finding up to two inflection points in the curve (t1 and t2). If there is no inflection point inside the curve we can call FlattenBezierCurveSegment directly, otherwise there is a whole bunch of interesting scenarios handled but not all cases appear to be taken into account, leading to some bezier curves not generating any vertex.

For example the following pseudo-svg:

> moveto 141.0 135.0
> curveto 141.0, 130.0, 140.0, 130.0, 131.0, 130.0
> close

doesn't get flattened properly. We find two inflection points t1=-0.125 and t2=1.0 and this combination does not make use go through any branch that produces vertices.

It looks like we are using strict float comparison against 0.0 and 1.0 in some places where we should be using >= or <=. In particular in the first branch: if an inflection point is exactly at 0.0 or 1.0, I think that we should consider it outside of the curve and be able to call FlattenBezierCurveSegment directly without splitting.
That, or handle these cases explicitly further down the function.
Attachment #8760696 - Flags: review?(bas) → review+
Whiteboard: [gfx-noted]
Pushed by
Fix bezier flattening when the inflection points are on the extremity of the curve. r=Bas
Closed: 4 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla50
Depends on: 1294969
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