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Asked: 2026-06-12T10:32:47+00:00

I have a chart generated using RaphaelJS library. It is just on long path:

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I have a chart generated using RaphaelJS library. It is just on long path:

M 50 122 L 63.230769230769226 130 L 76.46153846153845 130 L
89.6923076923077 128 L 102.92307692307692 56 L 116.15384615384615 106 L 129.3846153846154 88 L 142.6153846153846 114 L 155.84615384615384 52
L 169.07692307692307 30 L 182.3076923076923 62 L 195.53846153846152
130 L 208.76923076923077 74 L 222 130 L 235.23076923076923 66 L
248.46153846153845 102 L 261.6923076923077 32 L 274.9230769230769 130 L 288.15384615384613 130 L 301.38461538461536 32 L 314.6153846153846
86 L 327.8461538461538 130 L 341.07692307692304 70 L
354.30769230769226 130 L 367.53846153846155 102 L 380.7692307692308 120 L 394 112 L 407.2307692307692 68 L 420.46153846153845 48 L
433.6923076923077 92 L 446.9230769230769 128 L 460.15384615384613 110 L 473.38461538461536 78 L 486.6153846153846 130 L 499.8461538461538 56
L 513.0769230769231 116 L 526.3076923076923 80 L 539.5384615384614 58
L 552.7692307692307 40 L 566 130 L 579.2307692307692 94 L
592.4615384615385 64 L 605.6923076923076 122 L 618.9230769230769 98 L 632.1538461538461 120 L 645.3846153846154 70 L 658.6153846153845 82 L 671.8461538461538 76 L 685.0769230769231 124 L 698.3076923076923 110 L 711.5384615384615 94 L 724.7692307692307 130 L 738 130 L 751.2307692307692 66 L 764.4615384615385 118 L 777.6923076923076 70 L 790.9230769230769 130 L 804.1538461538461 44 L 817.3846153846154 130 L 830.6153846153845 36 L 843.8461538461538 92 L 857.076923076923 130 L 870.3076923076923 76 L 883.5384615384614 130 L 896.7692307692307 60 L 910 88

Also below these chart I have a jqueryUI slider of the same width (860px) and centered with the chart. I want when I move the slider to move a dot on the chart accordingly with the slider position. See attached screenshot:

start position

sliding behaviour

As you can see it seems to work fine. I’ve implemented this behaviour using the pathIntersection() method. On the slide event at each ui.value (x coordinate) I intersect my chartPath (the one from above) with a vertical straight line at the x coordinate.

But still there are some problems. One of them is that it runs very hard, and it kinda freezes sometimes.. and very weird sometimes it doesn’t seem to intersect at all even it should.. I’ll example below 2 cases I identified:

M 499.8461538461538 0 L 499.8461538461538 140

M 910 0 L 910 140

Could you please explain why this intersect behaviour happens (it should return a dot).. and the worst part it seems like it happens randomly.. if I use another chartdata.

Also if you can identify another (better) solution to syncronise the slider position with the dot on the chart.. would be perfect.

I thought about using Element.getPointAtLength(length), but I don’t know how. I think I should save the pathSegments and for each to compute the start Length and the finish Length.

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1 Answer

  1. Editorial Team

    I think it would be better to use the source data to find the intersection point manually. Shouldn’t be too hard as the points are already sorted by x.

    Path intersection appears to fail when you check the intersection at one of the vertices, which can be considered a bug but is not really surprising, since the library was never intended for computation geometry in the first place.

    By way of quick hack you could also try slightly modifying the x value when pathIntersection fails to produce a single value and checking again, e.g. try 499.8461538461538 + 0.0001 * (2 * Math.random() - 1) instead of just 499.8461538461538. You might need to try several times before you get a proper answer, but here it is unlikely. I believe the technique is generally known as perturbation.

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