Some neat uses for Texture Matrices

 (By Dan Evans, 10th Nov 1999)
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Please note; not all of these ideas have had solid testing via an implementation so some of it is theory, but not all of it.


The only real restriction on the coordinate space of these techniques is that if you want to use D3D's transformation pipeline (i.e. TnL) then you have to use world space coordinates for your vertex normals. This requires that the other vectors involved are also in the same coordinate space (otherwise the result would not make sense).

1) Cartoon rendering ('Toon' rendering)

Using this texture...

See actual results

and (D3DRENDERSTATE_TEXTUREMAPBLEND,D3DTBLEND_MODULATE) or (D3DTSS_COLOROP, D3DTOP_MODULATE) depending what your preferred method is. (I think the first pair are legacy now ???).


2) Anisotropic lighting

Using this texture...

See actual results

and (D3DRENDERSTATE_TEXTUREMAPBLEND,D3DTBLEND_ADD) or (D3DTSS_COLOROP, D3DTOP_ADD)


3) Spherical reflection mapping

This matrix uses the X and Y axes of the view matrix as vectors for using in a dot product with the world space normal (the D3D sample "Spheremapping" uses the world space normal which I found a bit confusing, but I guess that's how it works) The Z axis of the view matrix is ignored. What we want is a 2d mapping into our reflection map so Z turns out to be superfluous for our requirements. Using the D3D conventions the X axis in view space can be represented as a vector made from elements 11, 21, and 31 of the View matrix and 12, 22, 32 for the view-space Y axis;

Viewspace X Axis (VX)
_11 _12 _13 _14
_21 _22 _23 _24
_31 _32 _33 _34
_41 _42 _43 _44
Viewspace Y Axis (VY)
_11 _12 _13 _14
_21 _22 _23 _24
_31 _32 _33 _34
_41 _42 _43 _44




It is interesting to note that if you get a texture of a perfect ball of short fur on a black background and use that as your reflection map with a colourkey set to black (or similar with alphatest) then you can texture things with it to make a pseudo fur effect that presents "scalp" at vertices whose normals point to the camera position and gradually rotate out to sideways fur strands as the normal turns away from the camera until the normal is perpendicular to the camera direction. I have not yet been able to get hold of the perfect "ball of fur" image, so if anyone has one they wish to donate I would be extremely grateful. I call this technique "pseudo fur-mapping" :)
The jaggy edges at the circumference of the circle the ball makes on the 2d image provide the illusion of strands of fur at the silhouette of the fur-mapped object.
A very poor artists impression of what I mean...


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