Hi guys,
The help files give a pretty thorough explanation of how the value of a Bezier key .in/outTangentLength value is derived but doesn’t seem to mention anything that I can find about what the .in/outTangent value correlates to. When the value is positive the tangent “point” is above the key, when it’s negative it’s below the key and when it’s 0 the “point” is even with the key, so it looks like the value is some kind of offset relative to the key’s value but I can’t figure out the exact relationship. Like a key frame with a value of 30.00 that has an inTangent value of 1.00, I would think the inTangent value should equal 31.00… but it doesn’t. Does anybody know what the in/outTangent value is actually reflecting?
Thanks
Anyone?
What I’m trying to do is plot a bezier animation curve to a curveControl UI dialog. The curveControl wants Point2 values for the point tangents but the Bezier controller generates .in/outTangent and .in/outTangentLength values. I don’t understand how the Bezier controller calculates the .in/outTangent value to be able to plot the value as an [x,y] point in the curveControl’s “grid”. If I understood the math I could convert the Bezier values to a Point2 that the curveControl could use.
Im looking at this tomorrow for a colleague, but basically its the tangent of the keys bezier handle before and after the key. I.e going ‘in’ to the key and coming ‘out’ of it. Added a scribble from my moleskine.
cheers,
Hi Eek!
[img] http://forums.cgsociety.org/attachment.php?attachmentid=162473&stc=1 [/img]
So above, the inTangent is literally the trigonomic tangent value 0.067?
That would mean I could find the angle using the arcTangent of 0.067 which gives me 3.83309. Is that the literal angle of the tangent point relative to the key? This angle looks a lot bigger than 3.8 degrees:
[img] http://forums.cgsociety.org/attachment.php?attachmentid=162474&stc=1 [/img]
My understanding of trigonometry is terrible. Is this how Max is getting the value 0.067?
*EDIT – I think I was just zoomed in WAY too far on the Curve Editor. Anyway I zoomed out and put in an inTangent value of 1.0. The aTan of 1.0 is 45 degrees which looks about right in the Curve Editor.
Thanks for the help!!!
Edit: I need to fix my post
OK, aTan of .in/outTangent value gives the tangent angle. The .in/outTangentLength gives the length of the bottom of the “triangle” formed by the tangent (relative to the next key in the key array), which could be used as the x value of a point2 number for a graph (or the curveControl UI in this case).
For the y value:
y = the length of the side opposite from the angle’s tangent, and tangent(angle) = opposite length divided by bottom length so…
Doing the inverse of this: Tan (.in/outTangent) = y / (.in/outTangentLength) should get the length of y.
So, y = (.in/outTangentLength) * (.in/outTangent) finds the y value of the point2 number. Go math!
Does this seem right to you guys?