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ferhua

dot product problem in calculating reflective vector

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[attachment=33625:1.PNG]

The vector I and n are given, n is the unit vector, the output is vector r.

my question is the orientation of dot(n,l)*n.

Since dot(n,l) is the signed length(negative in this case)

why "the vector below n" still need to multiply by "n" ,  and why the vector dot(n,l)*n and "n" have opposite orientations.(assume that "dot(n,l)" is a scalar,after it multiply by "n", it should have the same direction as "n" )

[attachment=33626:??.PNG]

In my opinion ,it should be

[attachment=33627:??1q.PNG]

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why "the vector below n" still need to multiply by "n" ,  and why the vector dot(n,l)*n and "n" have opposite orientations.(assume that "dot(n,l)" is a scalar,after it multiply by "n", it should have the same direction as "n" )


You need to multiply by n to have a vector. Remember that the dot product is just a number (negative in this case, as you pointed out).

dot(n,l)*n and n point in opposite directions because dot(n,l) is negative. Negative scalars do that.

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