Incorrect normals in my exporter

Scripting in Blender with Python, and working on the API

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Joined: Mon Jun 05, 2006 7:46 am

Incorrect normals in my exporter

Post by Razor »

I'm making a custom exporter, and I'm having a bit of trouble getting vertex normals to come out properly. It seems to depend on the rotation of the object. If I create a sphere in the top viewport and export, it works perfectly. But if I create it in the front viewport, the y and z axes seem to be negated. I am transforming the the mesh using:

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m.transform(ob.getMatrix(), 1)
which the docs say should recalculate the normals. Do I have to convert them to world space myself somehow?

Thanks for your time. Oh, and I don't know python, I've been picking it up as I go along. So that could be the problem :wink:.

EDIT: Never mind, I just threw in a calcNormals() call and it seems to work. Thanks anyway! I won't delete the post though, on the off chance that someone can shed some light on the subject.

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Joined: Tue Nov 18, 2003 3:37 am

Post by macouno »

Yes you have to get the normals and vert locations in worldspace yourself if you want that.

Here's two functions that allow you to convert local coords into world coords.

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# Apply a matrix to a vert and return a vector.
def apply_transform(verts, matrix):
	x, y, z = verts
	xloc, yloc, zloc = matrix[3][0], matrix[3][1], matrix[3][2]
	return Mathutils.Vector(
	x*matrix[0][0] + y*matrix[1][0] + z*matrix[2][0] + xloc,
	x*matrix[0][1] + y*matrix[1][1] + z*matrix[2][1] + yloc,
	x*matrix[0][2] + y*matrix[1][2] + z*matrix[2][2] + zloc)

# Apply a matrix to a normal and return a vector.
def normal_transform(normal, matrix):
	matrix = matrix.rotationPart()
	x, y, z = normal
	return Mathutils.Vector(
	x*matrix[0][0] + y*matrix[1][0] + z*matrix[2][0],
	x*matrix[0][1] + y*matrix[1][1] + z*matrix[2][1],
	x*matrix[0][2] + y*matrix[1][2] + z*matrix[2][2])
Before you do this you have to get the worldspace matrix for that object like:

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tarObj = Object.Get('objectname')
	matrix = Mathutils.Matrix(tarObj.getMatrix('worldspace'));
that should help you along.

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Joined: Tue Feb 25, 2003 2:37 pm

Post by ideasman »

a cheating way willian and I added

# Now just use the verts and normals

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