Many years later, I’m glad I payed attention in my freshmen year geometry class.
Today I figured out rotations, something I thought I’d never done before, but as I did it I recalled it vaguely from out of the foggy memory that is high school mathematics.
A 2D rotation matrix is as follows:
| xcos(Ø) -ysin(Ø) |
| xsin(Ø) ycos(Ø) |
In this matrix, positive values will rotate counterclockwise. Also, theta must be in radians.
For a 3d application like Maya, the axis that you leave out (in this case, z) is the axis about which you will rotate. So if I wanted to rotate around the y axis, I’d have the variables x and z.
Matrices are fun and all, but I like direct formulas. And hooray! There is one!
x’ = xcos(Ø) – ysin(Ø)
y’ = xsin(Ø) + ysin(Ø)
For example, let’s say I want to rotate the vector [1,0] 90 degrees. That gives me:
x’ = 1(cos(90)) – 0(sin(90)) = 1(0) – 0(1) = 0
y’ = 1(sin(90)) + 0(sin(90)) = 1(1) + 0(1) = 1
So our new point it [0,1]. This works with any 2d vector and any degree.
Here’s a script of me applying some of this vector math. I use it to create an array of points and draw an nGon using those points. I then am able to rotate and scale that nGon. Baby steps!
import math import maya.cmds as cmds """ The equation for 2d rotation is: x' = xcos(theta) - ysin(theta) y' = xcos(theta) + ycos(theta) Positive values will rotate counterclockwise """ # our start vector p p = [1,0,0] # n is the number of sides on our nGon n = 16 # the arc variable determines the angle we need to rotate the start vector to make the points for the nGon. # For example, an equilateral triangle would have an arc value of 360/3 or 120 degrees. arc = 360 / n # A is our variable we'll use to store the current degree value a = arc # Store the verts in an array so we can mess with them later vertices =  # append our first point to the vertices array vertices.append(p) while a < 360: # rot value must be in radians rot = math.radians(a) newX = p * math.cos(rot) - p * math.sin(rot) newY = p * math.sin(rot) + p * math.cos(rot) newPnt = [newX,newY,0] vertices.append(newPnt) a += arc vertices.append(p) # try a 30 degree rotation along the y axis # start a at 1 a = 1 while a < len(vertices): rot = math.radians(30) newX = vertices[a] * math.cos(rot) - vertices[a] * math.sin(rot) newZ = vertices[a] * math.sin(rot) - vertices[a] * math.cos(rot) vertices[a] = newX vertices[a] = newZ a += 1 print("_") # it worked! now let's try scaling by .5 a = 1 while a < len(vertices): vertices[a] = vertices[a] * .5 vertices[a] = vertices[a] * .5 vertices[a] = vertices[a] * .5 a += 1 # now let's try moving up the y axis 1 unit a = 1 while a < len(vertices): vertices[a] = vertices[a] + 1 a += 1 # finally draw a curve to represent that shape. Pass it that array of points cmds.curve(d=1,point=vertices)