Processing 1.0 - Processing Discourse - tangent angle between 2 points

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tangent angle between 2 points (Read 1202 times)

glenn

tangent angle between 2 points
Jul 7^th, 2008, 10:27pm

Hi,
I'm trying to create a function that creates a curved triangle strip from a list of vertices - so I need to know how to get the 90 degree tangent angle between 2 points. I'm within beginshape() so cant use translate/rotate.

so for example i have point A (x,y) and point B (x,y), and need a third point at a rightangle tangent, to create the triangle aligning to the curve.

I was looking at vector3d libraries - there is a .cross method which calculates this for me i think- is this the right way to go? i'm still unsure,

thanks,
Glenn.

http://www.butterfly.ie

antiplastik YaBB Moderator Offline Posts: 699 France	Re: tangent angle between 2 points Reply #1 - Jul 7^th, 2008, 10:51pm i think you'll figure something out with atan2 : http://processing.org/reference/atan2_.html

glenn Junior Member Offline Posts: 86	Re: tangent angle between 2 points Reply #2 - Jul 7^th, 2008, 11:18pm I've used atan before to get what I want, but because I'm inside a beginshape() function, i cant use translate/rotate to make use of atan. my vertex list also part of a particle class which isnt affected by translate/rotate either. so it will have to be lots of math or maybe that .cross vector method.
	http://www.butterfly.ie

JohnG

Re: tangent angle between 2 points
Reply #3 - Jul 8^th, 2008, 12:02am

Code:

float x1,y1,x2,y2; 
float width;
//set these to the values of the two points...
float ang=atan2(y2-y1,x2-x1)+HALF_PI; //might be -HALF_PI
float x3=width*cos(ang); //might be sin..
float y3=width*sin(ang); //might be cos if above is sin

glenn Junior Member Offline Posts: 86	Re: tangent angle between 2 points Reply #4 - Jul 8^th, 2008, 10:28am Thanks John, I'll try this out today. G.
	http://www.butterfly.ie

glenn Junior Member Offline Posts: 86	Re: tangent angle between 2 points Reply #5 - Jul 8^th, 2008, 4:32pm Brilliant John Thanks, I then added x3,y3 to x1,y1 to get the final coordinate for the triangle. Working okay now. Cheers, G.
	http://www.butterfly.ie

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