生成多边形的顶点

Question

I'm trying to make a useful/generic 2D polygon class for an OpenGL ES renderer. When I create a polygon, I give it several parameters:

Polygon(Vector3 centerpoint, int numVertices, float inPolySize)

Then, I try to generate the vertices. This is where i'm having a tough time. I need to determine the number of vertices, get an angle, find the x/y position of that angle, someone take the size into account, AND offset by the position.

OpenGL works with big arrays of data. Nothing is nice like Lists of Vector3's. Instead it's float[] arrays, with the first index being X1, second being Y1, third being Z1, fourth being X2, etc...

final int XPOS = 0;
final int YPOS = 1;
final int ZPOS = 2;
int mvSize = 3; // (x, y, z);
float[] vertices = new float[mvSize * mNumVertices];
for (int verticeIndex = 0; verticeIndex < mNumVertices; verticeIndex++)
{
    double angle = 2 * verticeIndex * Math.PI / mNumVertices;
    vertices[mvSize * verticeIndex + XPOS] = (((float)Math.cos(angle)) * mPolygonSize) + mPosition.GetX();
    vertices[mvSize * verticeIndex + YPOS] = (((float)Math.sin(angle)) * mPolygonSize) + mPosition.GetY();
    vertices[mvSize * verticeIndex + ZPOS] = mPolygonSize + mPosition.GetZ();
}

Unfortunatley, my triangle is never quite right. It's skewed a lot, the size doesn't seem right...

I figure i'm throwing the size into the wrong formula, can anyone help?

EDIT: Here's some sample data Polygon test = new Polygon( new Vector3(0, 1, 0), 3, .5f);

vertices[0] = -0.25

vertices[1] = 1.4330127

vertices[2] = 0.0

vertices[3] = -0.25

vertices[4] = 0.5669873

vertices[5] = 0.0

vertices[6] = 0.5

vertices[7] = 1.0

vertices[8] = 0.0

vertices[9] = -0.25

vertices[10] = 1.4330127

vertices[11] = 0.0

Answer 1

I can't believe I was this stupid. Basically, my render window was smaller than my screen. If my screen is a rectangle, my render window was a square.

This being the case, any triangle I draw that was up was clipped by my render window. To me, it looked like the triangle was skewed. Really, it was just clipped!

Answer 2

The Java math library takes radians as input, not degrees. I didn't see the angles you were using for your calculation, but if you're not converting to radians from degrees, you will get some skewed looking shapes, and would explain that your calculations are correct, but the expected result is off.