Sharp DX Identity Matrix, Matrix.Forward vector pointing at negative Z

Question

I'm trying to take a steady grip on Sharp DX. Already done some work like translating, scaling and rotating objects. Now i have to calculate the rotation matrix using only direction vector and arbitrary UP vector which is Unit Y vector (0,1,0). And this is where everything I know about Direct X graphics falls apart: I filled the Matrix.Forward with the normalized DIRECTION vector, and then crossed it with arbitrary UP (exactly this: DIR cross UP, not the other way), the resulting vector put in Matrix.Right property. Now if I put (0,1,0) in the Matrix.Up property, my model is facing the exact opposite direction to the expected direction (it faces backwards). Further investigation brought me to the fact that the Matrix.Identity matrix faces the NEGATIVE Z direction, which is weird to me as I thought that Identity would face positive X,Y,Z axes. Now I can overcome my problems by flipping any of the axes, but this clearly is not comforting to me, as there is something i must have missed in the meantime. So the ultimate question is: Why my Identity matrix points positive Y axis (good), positive X axis (nice, i expect this) and NEGATIVE Z (help!)

Answer 1

A cross product gives you the perpendicular line. Both the negative and the positive vector represent the same perpendicular line. You'll have to change your order of operations to get the positive vector. Eg. DIR cross UP and UP cross DIR will give the same perpendicular line but might change the sign of the vector. (It's too early to do matrix computations to show that :P)