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Question by anurp · Apr 01, 2015 at 01:19 PM · shader writing

Shader related question


Hi, Positing this on behalf of friend of mine who had a couple of questions about Shaders :

In a basic diffuse vertex shader, you multiply the vertex normal with the worldtobject matrix and then get the cosine of the angle between the normal and the worldspacelightpos0 which is the direction of the directional light How can you have the first in object space and the second in worldspace ? Should they not belong to the same coordinate spaces ?

Most tutorials on the internet for diffuse shaders have this code. For example, the diffuse shader mentioned in the link below.

http://en.wikibooks.org/wiki/Cg_Programming/Unity/Diffuse_Reflection

Similar to this is the specular reflection question.

For getting the specular highlight, one has to get the cosine of the angle between the reflected light and viewdirection. In some tutorials I have seen that to calculate the view vector, they subtract the _worldspacecamerapos from the vertex position transformed by the model view projection matrix, this transforming the vector into view space. Again how can the camera pos be in world space when the vertex position is in the view space ?

Thanks

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avatar image joelv · Apr 02, 2015 at 10:27 AM 0
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You are absolutely correct in that vector operations should be done in the same space. In the case of lighting this is usually world or view space. It's up to the shader writer to decide in what space lighting and other operations are done.

There are usually a set of matrices sent to the vertex shader. $$anonymous$$ost notable one that transforms from object to world space (Object2World) and one that transforms from object to projected view space (UNITY$$anonymous$$ATRIX_$$anonymous$$VP).

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