JohnBlackburne If you know two then you can find the third, but by the time you have set up and are exporting the normal + tangent you might as well export the binormal too.
I decided to compare the tangents and bitangents I generate, with tangents I export. Was looking for an export file type that has the option of exporting tangents, found the FBX format, and exported the file here are the result of exporting a simple quad made of 2 triangles with 3D Max exporter tangents compared to my generated ones:
exported ones:
positions
-18.1205348968506,-28.067813873291,3.93030738830566,18.1205348968506,-28.067813873291,3.93030738830566,-18.1205348968506,-6.9321870803833,28.4147491455078,18.1205348968506,-6.9321870803833,28.4147491455078,18.1205348968506,-6.9321870803833,28.4147491455078,-18.1205348968506,-28.067813873291,3.93030738830566
normals
0,-0.756976366043091,0.65344226360321,0,-0.756976366043091,0.653442323207855,0,-0.756976366043091,0.653442323207855,0,-0.756976366043091,0.65344226360321,0,-0.756976366043091,0.65344226360321,0,-0.756976366043091,0.65344226360321
Binormals: *18 {
-0,0.65344226360321,0.756976366043091,-0,0.653442323207855,0.756976366043091,-0,0.65344226360321,0.756976366043091,-0,0.65344226360321,0.756976366043091,-0,0.653442323207855,0.756976366043091,-0,0.65344226360321,0.756976366043091
Tangents: *18 {
1,0,0,1,0,0,1,0,0,1,0,0,1,0,0,1,0,0
}
and now mine:
positions 15
-18.120537,-28.067816,3.930309,18.120535,-28.067816,3.930309,18.120535,-6.932187,28.414749,-18.120537,-6.932187,28.414749,-18.120537,-28.067816,3.930309
normals
0,-0.756976336120277,0.6534422901480444,0,-0.756976336120277,0.6534422901480444,0,-0.756976336120277,0.6534422901480444,0,-0.756976336120277,0.6534422901480444,0,-0.756976336120277,0.6534422901480444
tangents
1,0,0,1,0,0,1,0,0,1,0,0,1,0,0
bitangents
0,-0.6534423476127358,-0.7569762865152095,0,-0.6534423476127358,-0.7569762865152095,0,-0.6534423476127358,-0.7569762865152095,0,-0.6534423476127358,-0.7569762865152095,0,-0.6534423476127358,-0.7569762865152095
as you can see they are identical (mine is one vertex less because my optimization function) the only difference is between the binormals of the FBX file and my bitangents, the difference is only in the positive or negative sign of the number, the rest is identical.
but still something is wrong with the lightning, though I'm not using binormals, I wonder what will happen if I'll try to calculate the bitangents from the normals and the tangents, do you have the formula for calculating this?