Unity - Improve Mesh generation and rendering performance - performance

Question

since I just recently started looking into meshes, how they work, what they do and so on, I decided to use my own calculations to create a mesh of a circle. Unfortunately though, this is really, really slow!
So I am looking for tips on improvements, to make it slow only (because that's probably the best it will get...)
Here is the code I use to generate a circle:
public static void createCircle(MeshFilter meshFilter, float innerRadius, float outerRadius, Color color, float xPosition = 0, float yPosition = 0, float startDegree = 0, float endDegree = 360, int points = 100)
{
Mesh mesh = meshFilter.mesh;
mesh.Clear();
//These values will result in no (or very ugly in the case of points < 10) circle, so let's safe calculation and just return an empty mesh!
if (startDegree == endDegree || points < 10 || innerRadius >= outerRadius || innerRadius < 0 || outerRadius <= 0)
{
return;
}
//The points for the full circle shall be whatever is given but if its not the full circle we dont need all the points!
points = (int)(Mathf.Abs(endDegree - startDegree) / 360f * points);
//We always need an uneven number of points!
if (points % 2 != 0) { points++; }
Vector3[] vertices = new Vector3[points];
float degreeStepSize = (endDegree - startDegree) * 2 / (points - 3);
float halfRadStepSize = (degreeStepSize) * Mathf.Deg2Rad / 2f;
float startRad = Mathf.Deg2Rad * startDegree;
float endRad = Mathf.Deg2Rad * endDegree;
//Let's save the vector at the beginning and the one on the end to make a perfectly straight line
vertices[0] = new Vector3(Mathf.Sin(startRad) * outerRadius + xPosition, Mathf.Cos(startRad) * outerRadius + yPosition, 0);
vertices[vertices.Length - 1] = new Vector3(Mathf.Sin(endRad) * innerRadius + xPosition, Mathf.Cos(endRad) * innerRadius + yPosition, 0);
for (int i = 1; i < vertices.Length - 1; i++)
{
//Pure coinsidence that saved some calculatons. Half Step Size is the same as what would needed to be calculated here!
float rad = (i - 1) * halfRadStepSize + startRad;
if (i % 2 == 0)
{
vertices[i] = new Vector3(Mathf.Sin(rad) * outerRadius + xPosition, Mathf.Cos(rad) * outerRadius + yPosition, 0);
}
else
{
vertices[i] = new Vector3(Mathf.Sin(rad) * innerRadius + xPosition, Mathf.Cos(rad) * innerRadius + yPosition, 0);
}
}
mesh.vertices = vertices;
int[] tri = new int[(vertices.Length - 2) * 3];
for (int i = 0; i < (vertices.Length - 2); i++)
{
int index = i * 3;
if (i % 2 == 0)
{
tri[index + 0] = i + 0;
tri[index + 1] = i + 2;
tri[index + 2] = i + 1;
}
else
{
tri[index + 0] = i + 0;
tri[index + 1] = i + 1;
tri[index + 2] = i + 2;
}
}
mesh.triangles = tri;
Vector3[] normals = new Vector3[vertices.Length];
Color[] colors = new Color[vertices.Length];
for (int i = 0; i < vertices.Length; i++)
{
normals[i] = Vector3.forward;
colors[i] = color;
}
mesh.normals = normals;
mesh.colors = colors;
meshFilter.mesh = mesh;
}
I know I "could just use the LineRenderer shipped with Unity, it is faster then anything you'll ever write", but that's not the point here.
I am trying to understand meshes and see where I can tweak my code to improve it's performance.
Thanks for your help in advance!

Answer 1

You can almost double the speed by removing extra memory allocation. Since Vector3 is a value type, they are already allocated when you allocate the array. Vector3.forward also allocates a new Vector3 each time, and we can re-use it.
public static void createCircle(MeshFilter meshFilter, float innerRadius, float outerRadius, Color color, float xPosition = 0, float yPosition = 0, float startDegree = 0, float endDegree = 360, int points = 100)
{
Mesh mesh = meshFilter.mesh;
mesh.Clear();
//These values will result in no (or very ugly in the case of points < 10) circle, so let's safe calculation and just return an empty mesh!
if (startDegree == endDegree || points < 10 || innerRadius >= outerRadius || innerRadius < 0 || outerRadius <= 0)
{
return;
}
//The points for the full circle shall be whatever is given but if its not the full circle we dont need all the points!
points = (int)(Mathf.Abs(endDegree - startDegree) / 360f * points);
//We always need an uneven number of points!
if (points % 2 != 0) { points++; }
Vector3[] vertices = new Vector3[points];
float degreeStepSize = (endDegree - startDegree) * 2 / (points - 3);
float halfRadStepSize = (degreeStepSize) * Mathf.Deg2Rad / 2f;
float startRad = Mathf.Deg2Rad * startDegree;
float endRad = Mathf.Deg2Rad * endDegree;
//Let's save the vector at the beginning and the one on the end to make a perfectly straight line
vertices[0] = new Vector3(Mathf.Sin(startRad) * outerRadius + xPosition, Mathf.Cos(startRad) * outerRadius + yPosition, 0);
vertices[vertices.Length - 1] = new Vector3(Mathf.Sin(endRad) * innerRadius + xPosition, Mathf.Cos(endRad) * innerRadius + yPosition, 0);
for (int i = 1; i < vertices.Length - 1; i++)
{
//Pure coinsidence that saved some calculatons. Half Step Size is the same as what would needed to be calculated here!
float rad = (i - 1) * halfRadStepSize + startRad;
if (i % 2 == 0)
{
vertices[i].x = Mathf.Sin(rad) * outerRadius + xPosition;
vertices[i].y = Mathf.Cos(rad) * outerRadius + yPosition;
vertices[i].z = 0;
}
else
{
vertices[i].x = Mathf.Sin(rad) * innerRadius + xPosition;
vertices[i].y = Mathf.Cos(rad) * innerRadius + yPosition;
vertices[i].z = 0;;
}
}
mesh.vertices = vertices;
int[] tri = new int[(vertices.Length - 2) * 3];
for (int i = 0; i < (vertices.Length - 2); i++)
{
int index = i * 3;
if (i % 2 == 0)
{
tri[index + 0] = i + 0;
tri[index + 1] = i + 2;
tri[index + 2] = i + 1;
}
else
{
tri[index + 0] = i + 0;
tri[index + 1] = i + 1;
tri[index + 2] = i + 2;
}
}
mesh.triangles = tri;
Vector3[] normals = new Vector3[vertices.Length];
Color[] colors = new Color[vertices.Length];
var f = Vector3.forward;
for (int i = 0; i < vertices.Length; i++)
{
normals[i].x= f.x;
normals[i].y= f.y;
normals[i].z= f.z;
colors[i] = color;
}
mesh.normals = normals;
mesh.colors = colors;
meshFilter.mesh = mesh;
}