Hello everybody!
I’m trying to bump map simple quad(draw it using tris_strip) using ARB_tex_env_dot3 and vertex program.
I calculate lights position in object space and then calculate light vector (lights position in object space – vertex.position), normalize vector and transform it in tangent space. For my quad facing viewer texture matrix looks like this:
T 1,0,0
B 0,1,0
N 0,0,1
I store this vector in result.color and store vertex.texcoord[0] in result.texcoord[0].
Well, problem is that when I try to use normal map generated with Nvidias Photoshop plugin I get incorect results when I try to rotate quad around x-axis. It seems that I get correct results when I invert green chanel in normal map or if I use (0, -1, 0) for binormal.
I think that texture matrix is correct, but in SimpleDot3 demo on ATIs website they use 0, -1, 0 for binormal and they use only one quad just like me. I even tried using NVMeshMender for generating tangent and binormal and I get 1,0,0 and 0,1,0.
So question is is this texture matrix correct for this quad:
//vertices
V0 –0.5, -0.5, 0.0
V1 0.5, -0.5, 0.0
V2 –0.5, 0.5, 0.0
V3 0.5, 0.5, 0.0
// texcoords
VT0 0.0, 0.0
VT1 1.0, 0.0
VT2 0.0, 1.0
VT3 1.0, 1.0
//normal
VN 0.0, 0.0, 1.0
or there is bug in normal map plugin, or something else?
Thanks!
The choice of a basis for tangent space is somewhat arbitrary, so it is just a matter of keeping your code and art in synch.
It is reasonable to have the tangent vector point in the direction of s, -s, t, or -t. The only thing that is important is to stay self consistent.
-Evan
…like always using blue for ‘up’. 