Multiplication by a view matrix does not affect the resulting value in OpenGL ES 2.0/3.0

Question

To obtain constant directional light, I multiplied the view matrix by the light direction vector:

#version 300 es
uniform mat4 u_mvMatrix; // model-view matrix
uniform mat4 u_vMatrix; // view matrix
in vec4 a_position;
in vec3 a_normal;
const vec3 lightDirection = vec3(-1.9, 0.0, -5.0);
...
void main() {
    vec3 modelViewNormal = vec3(u_mvMatrix * vec4(a_normal, 0.0));
    vec3 lightVector = -(mat3(u_vMatrix) * lightDirection);
    float diffuseFactor = max(dot(modelViewNormal, lightVector), 0.0);
    ...
}

But the diffuseFactor value is the same as when use:

vec3 lightVector = -lightDirection;

In other words, it turns out the same worst picture.

Question: Can anyone please suggest why multiplication by a view matrix does not affect the resulting value diffuseFactor?

Note: The view matrix is created using:

Matrix.setLookAtM(viewMatrix, rmOffset:0, eyeX:0f, eyeY:0f, eyeZ:0f,
        centerX:0f, centerY:0f, centerZ:-4f, upX:0f, upY:1f, upZ:0f)
fun getVMatrixAsFloatBuffer(): FloatBuffer = Buffers.floatBuffer(viewMatrix)
GLES20.glUniformMatrix4fv(vMatrixLink, 1, false, view.getVMatrixAsFloatBuffer());

I also checked the correctness of the view matrix using:

gl_Position = u_pMatrix * u_vMatrix * u_mMatrix * a_position;

This is working fine.

Thanks in advance!

Answer 1

The view matrix

Matrix.setLookAtM(viewMatrix, 0, 0f, 0f, 4f, 0.0f, 0f, 0f, 0f, 1.0f, 0.0f)

does not affect the viewing directing, because the upper left 3x3 of the view matrix is the Identity matrix.

Hence the operation

vec3 lightVector = -(mat3(u_vMatrix) * lightDirection);

multiplies the vector lightDirection by the identity matrix and doesn't change the vector at all.

Use different a point of view, to see the effect of the view matrix. For Instance:

Matrix.setLookAtM(viewMatrix, 0f, 0f, 2.8f, 2.8f, 0.0f, 0f, 0f, 0f, 1.0f, 0.0f)