Tidbit - Texture alignment on an arbitrary surface

seed · by **seed** » Wed May 12, 2010 9:41 pm

Problem - creating texture coordinates for an arbitrary surface. A surface is defined as a plane and n vertices on the plane that define the triangles of the surface. If you don't have texture coordinates, how can you create some that make sense and don't stretch/warp your texture.

Solution - create two axis vectors, xaxis and yaxis, for your surface. The texture coordinates are simply the dot product of each vertex to these vectors.

Syntax: [ Download ] [ Hide ]

Using java Syntax Highlighting

Vector3 xaxis = new Vector3();
 
Vector3 yaxis = new Vector3();
 
Vector3 down = new Vector3();
 
// The xaxis is the real x-axis if the plane is parallel to the xy plane, (normal is 0,0,+-1)
 
// Otherwise, the xaxis is the cross product of 'down' and the plane normal
 
if ((Math.abs(plane.normal.z) == 1) && (plane.normal.x == 0) and (plane.normal.y == 0))
 
{
 
   Vector3.set(xaxis,1,0,0);
 
}
 
else
 
{
 
   Vector3.set(down,0,0,-1);
 
   Vector3.cross_product(xaxis, down, plane.normal);
 
   Vector3.normalize(xaxis,xaxis);
 
}
 
// The yaxis is the cross of the xaxis and the plane normal
 
Vector3.cross_product(yaxis,plane.normal,xaxis);
 
Vector3.normalize(yaxis,yaxis);
 
// For each of your vertices, the x and y texture coordinates are the dot products respective to 
 
// these newly created x and y axis vectors.
 
for (int i=0; i<number_of_vertices; i++)
 
{
 
   texture_vertex[i].x = Vector3.dot_product(vertex[i],xaxis) * texture_scale;
 
   texture_vertex[i].y = Vector3.dot_product(vertex[i],yaxis) * texture_scale;
 
}
 
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Tidbit - Texture alignment on an arbitrary surface

Tidbit - Texture alignment on an arbitrary surface

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