using UnityEngine;

[ExecuteInEditMode]
public class ProceduralCylinder : MonoBehaviour
{
	public Mesh m_CylinderMesh = null;
	public Material m_Material = null;
	public int m_RadiusSubdivisions = 10;
	public int m_HeightSubdivisions = 5;
	public float m_Radius = 1.0f;
	public float m_Height = 5.0f;

	private Vector3[] m_Vertices;
	private Vector2[] m_UVs;
	private int[] m_Triangles;

	[ContextMenu("Generate Mesh")]
	public void GenerateMesh()
	{
		if(m_CylinderMesh != null)
		{
			if(Application.isPlaying)
			{
				Destroy(m_CylinderMesh);
			}
			else
			{
				DestroyImmediate(m_CylinderMesh);
			}
		}

		m_CylinderMesh = new Mesh();
		m_CylinderMesh.name = "Cylinder_" + gameObject.name;

		m_Vertices = new Vector3[(m_HeightSubdivisions + 1) * m_RadiusSubdivisions];
		m_UVs = new Vector2[m_Vertices.Length];
		m_Triangles = new int[6 * m_HeightSubdivisions * m_RadiusSubdivisions];
		int currentTriangle = 0;

		for(int i = 0; i < m_HeightSubdivisions + 1; i++)
		{
			float yUV = ((float)i / (float)m_HeightSubdivisions);
			float height = yUV * m_Height;

			for(int j = 0; j < m_RadiusSubdivisions; j++)
			{
				float xUV =  ((float)j / (float)m_RadiusSubdivisions);
				float rad = xUV * Mathf.PI * 2.0f;
				Vector3 pos = new Vector3(Mathf.Cos(rad) * m_Radius, height, Mathf.Sin(rad) * m_Radius);
				int idx0 = (i * m_RadiusSubdivisions + j);
				m_Vertices[idx0] = pos;
				m_UVs[idx0] = new Vector2(xUV, yUV);

				if(i < m_HeightSubdivisions)
				{
					int idx1 = ((i + 1) * m_RadiusSubdivisions + j);
					int idx2 = ((i + 1) * m_RadiusSubdivisions + ((j + 1) % m_RadiusSubdivisions));
					int idx3 = (i * m_RadiusSubdivisions + ((j + 1) % m_RadiusSubdivisions));

					m_Triangles[currentTriangle + 0] = idx0;
					m_Triangles[currentTriangle + 1] = idx1;
					m_Triangles[currentTriangle + 2] = idx2;

					m_Triangles[currentTriangle + 3] = idx0;
					m_Triangles[currentTriangle + 4] = idx2;
					m_Triangles[currentTriangle + 5] = idx3;

					currentTriangle += 6;
				}
			}
		}

		m_CylinderMesh.vertices = m_Vertices;
		m_CylinderMesh.uv = m_UVs;
		m_CylinderMesh.triangles = m_Triangles;

		m_CylinderMesh.RecalculateBounds();
		m_CylinderMesh.RecalculateNormals();
		m_CylinderMesh.RecalculateTangents();
	}

	private void Update()
	{
		Camera camera = Camera.main;
		if(m_CylinderMesh != null)
		{
			Graphics.DrawMesh(m_CylinderMesh, transform.localToWorldMatrix, m_Material, gameObject.layer);
		}
	}
}