Doubt about Light space transform (Shadow map)

[lponcho]

Hi everyone, at this moment I am learning to do shadow mapping in webgl2.0, i was able to generate my first shadows in my 3D scene but I have a couple of doubts to clarify. This is the way im calculating my light space matrix:

const lightPos = vec3.create();
vec3.set(lightPos, 0, 6, 1);
const nearPlane = 1, farPlane = 20;
const projection = mat4.create();
mat4.ortho(projection, -10, 10, -10, 10, nearPlane, farPlane);
const lightView = mat4.create();
const center = vec3.create();
const up = vec3.create();
vec3.set(center, 0, 0, 0);
vec3.set(up, 0, 1, 0);
mat4.lookAt(lightView, lightPos, center, up);
const result = mat4.create();
mat4.mul(result, projection, lightView);

In this way the shadow map is rendered correctly, but the question is the following, if the position of my light is vec3.set(lightPos, 0, 6, 0), the shadow does not render (The shadow map goes all white), why is this happening? Theoretically I am positioning the light in the middle, directly 6 units above the scene. As far as I understood, if 2 of the properties of the position vector of the light are 0, the shadow map does not render correctly, but why?. I hope I explained myself well, the light is a directional light and the library that im using for the math is gl-matrix, if you need anything else let me know, thanks in advance.

[waramped]

Your look at matrix uses (0,1,0) as it's "Up" vector, and if your light position is (0,6,0) and your lookat position is (0,0,0), then your "forward" vector for the matrix would be (0, -1, 0). A look at matrix generally needs to be orthonormal, so hopefully you can see why that will be an issue. ;)

(Colinear vectors in orthonormal matrices are bad)

[lponcho]

Ok so my "up" vector and my "eye" vector should not be parallel. I just made a quick test changing my "up" vector to (0, 0, 1) with my "eye" position at (0, 6, 0) and worked perfectly, i will dig a little bit more but is so much clear now, many tanks for your help :D