PaintCode - move object on the path

问题

I would like draw a curved line and attach an object to it. Is it possible to create fraction (from 0.0 to 1.0) which makes move my object on the path? When fraction is 0 then object is on the beginning, when 0.5 is on half way and finally when is on 1.0 it is at the end. Of course i want a curved path, not a straight line :) Is it possible to do in PaintCode?

回答1:

If you need it only as a progress bar, it is possible in PaintCode. The trick is to use dashed stroke with very large Gap and then just change the Dash.

Then just attach a Variable and you are done.

Edit: Regarding the discussion under the original post, this solution uses points as the unit, so it will be distributed equally along the curve, no matter how curved the bezier is.

回答2:

Based on the fact that you're going to walk along the curve using linear distance, a thing Bezier curves are terrible for, you need to build the linear mapping yourself. That's fairly simple though:

When you draw the curve, also build a look-up table that samples the curve once, at say 100 points (t=0, t=0.01, t=0.02, etc). In pseudocode:

lut = [];
lut[0] = 0;
tlen = curve.length();
for(v=0; v<=100; v++) {
  t = v/100;
  clen = curve.split(0,t).length();
  percent = 100*clen/tlen;
  lut[percent] = t;
}

This may leave gaps in your LUT - you can either fix those as a secondary step, or just leave them in and do a binary scan on your array to find the nearest "does have a value" percentage.

Then, when you need to show your progress as some percentage value, you just look up the corresponding t value: say you need to show 83%, you look up lut[83] and draw your object at the value that gives you.

来源：https://stackoverflow.com/questions/32943343/paintcode-move-object-on-the-path

标签

ios

swift

paint

bezier