Quite some time ago i’ve written a small script that can create a mesh out of a texture. Can’t remember if this was before the “2d update” of Unity or not anyways it doesn’t use sprites but plain textures:
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
[RequireComponent(typeof(MeshFilter), typeof(MeshRenderer))]
public class ExtrudeSprite : MonoBehaviour
{
private enum Edge {top, left, bottom, right};
public Material spriteMat;
public int alphaTheshold = 0;
public float depth = 0.0625f;
private Color32[] m_Colors;
private int m_Width;
private int m_Height;
private List<Vector3> m_Vertices = new List<Vector3>();
private List<Vector3> m_Normals = new List<Vector3>();
private List<Vector2> m_TexCoords = new List<Vector2>();
private bool HasPixel(int aX, int aY)
{
return m_Colors[aX + aY*m_Width].a > alphaTheshold;
}
void AddQuad(Vector3 aFirstEdgeP1, Vector3 aFirstEdgeP2,Vector3 aSecondRelative, Vector3 aNormal, Vector2 aUV1, Vector2 aUV2, bool aFlipUVs)
{
m_Vertices.Add(aFirstEdgeP1);
m_Vertices.Add(aFirstEdgeP2);
m_Vertices.Add(aFirstEdgeP2 + aSecondRelative);
m_Vertices.Add(aFirstEdgeP1 + aSecondRelative);
m_Normals.Add(aNormal);
m_Normals.Add(aNormal);
m_Normals.Add(aNormal);
m_Normals.Add(aNormal);
if (aFlipUVs)
{
m_TexCoords.Add(new Vector2(aUV1.x,aUV1.y));
m_TexCoords.Add(new Vector2(aUV2.x,aUV1.y));
m_TexCoords.Add(new Vector2(aUV2.x,aUV2.y));
m_TexCoords.Add(new Vector2(aUV1.x,aUV2.y));
}
else
{
m_TexCoords.Add(new Vector2(aUV1.x,aUV1.y));
m_TexCoords.Add(new Vector2(aUV1.x,aUV2.y));
m_TexCoords.Add(new Vector2(aUV2.x,aUV2.y));
m_TexCoords.Add(new Vector2(aUV2.x,aUV1.y));
}
}
void AddEdge(int aX, int aY, Edge aEdge)
{
Vector2 size = new Vector2(1.0f/m_Width, 1.0f/m_Height);
Vector2 uv = new Vector3(aX*size.x, aY*size.y);
Vector2 P = uv - Vector2.one*0.5f;
uv += size*0.5f;
Vector2 P2 = P;
Vector3 normal;
if (aEdge == Edge.top)
{
P += size;
P2.y += size.y;
normal = Vector3.up;
}
else if(aEdge == Edge.left)
{
P.y += size.y;
normal = Vector3.left;
}
else if(aEdge == Edge.bottom)
{
P2.x += size.x;
normal = Vector3.down;
}
else
{
P2 += size;
P.x += size.x;
normal = Vector3.right;
}
AddQuad(P, P2, Vector3.forward*depth, normal, uv,uv,false);
}
void GenerateMesh()
{
Texture2D tex = spriteMat.mainTexture as Texture2D;
m_Colors = tex.GetPixels32();
m_Width = tex.width;
m_Height = tex.height;
// first point , second point , relative 3. P, normal, lower UV, Upper UV, flipUV
AddQuad(new Vector3(-0.5f, -0.5f, 0 ), new Vector3(-0.5f, 0.5f, 0 ), Vector3.right, Vector3.back, Vector2.zero, Vector2.one, false);
AddQuad(new Vector3(-0.5f, -0.5f, depth), new Vector3( 0.5f, -0.5f, depth), Vector3.up, Vector3.forward, Vector2.zero, Vector2.one, true);
for (int y = 0; y < m_Height; y++) // bottom to top
{
for (int x = 0; x < m_Width; x++) // left to right
{
if (HasPixel(x,y))
{
if(x==0 || !HasPixel(x-1,y))
AddEdge(x,y,Edge.left);
if(x==m_Width-1 || !HasPixel(x+1,y))
AddEdge(x,y,Edge.right);
if(y==0 || !HasPixel(x,y-1))
AddEdge(x,y,Edge.bottom);
if(y==m_Height-1 || !HasPixel(x,y+1))
AddEdge(x,y,Edge.top);
}
}
}
var mesh = new Mesh();
mesh.vertices = m_Vertices.ToArray();
mesh.normals = m_Normals.ToArray();
mesh.uv = m_TexCoords.ToArray();
int[] quads = new int[m_Vertices.Count];
for (int i = 0; i < quads.Length; i++)
quads[i] = i;
mesh.SetIndices(quads,MeshTopology.Quads,0);
GetComponent<MeshFilter>().sharedMesh = mesh;
}
void Start()
{
GenerateMesh();
}
}
Just attach the script to an empty gameobject and assign a material with a readable texture to the “spriteMat” variable. The “depth” specifies the extrude depth. (Just in case you wonder why 0.0625 that’s 1/16 because it’s a 16x16 texture. That way the depth is as large as the pixels) The mesh will have a size of one by one world units. The pivot is in the center of the actual image but on the front side. The mesh is extruded along the z axis. So the front side is at local z=0 while the back side is at local z=depth.
I don’t generate a quad or cube for each pixel. I just use one quad for the whole front and one quad for the whole back side. Only the edges in between are generated and only those which aren’t hidden (so edges that have a transparent neighbor). So it’s like a very primitive version of the marching squares algorithm.
edit
Just in case someone wonders why i’ve written this. I’ve started a Turtle simulator but the project is on hold for the moment 
(I apologize for any mistake in my English…)