get screen position using mvp matrix in script

hi

i'm studying about projection matrix. i think mvp * localModel position is screen position

but when i try below code it display difference result.

what am i wrong?

can anyone explain this would be thankful.

Matrix4x4 m = transform.localToWorldMatrix;
Matrix4x4 v = Camera.mainCamera.worldToCameraMatrix;
Matrix4x4 p = Camera.mainCamera.projectionMatrix;

Matrix4x4 MVP = p*v*m;

Mesh mesh = gameObject.GetComponent<MeshFilter>().mesh;
Vector3[] vertices = mesh.vertices;

int i = 0;
while (i < vertices.Length) {

print(MVP.MultiplyPoint(vertices)); // <-- i expect this result same as WorldToScreenPoint but it's not!
print(Camera.mainCamera.projectionMatrix.MultiplyPoint(vertices));
print(Camera.mainCamera.WorldToScreenPoint(vertices));
i++;
}

 

try m*v*p

 

After vertex transformed by mvp, it is in clip space ,not in screen space,either(-1,1) nor (screen.width,screen.height)

 

I have same problem.

why MVP.MultiplyPoint(vertices) is not same as WorldToScreenPoint?

 

You should use this:


Matrix4x4 matrix = _3dCamera.projectionMatrix * _3dCamera.worldToCameraMatrix;
Vector3 screenPos = matrix.MultiplyPoint(newObj.transform.position);

// (-1, 1)'s clip => (0 ,1)'s viewport
screenPos= new Vector3(screenPos.x + 1f, screenPos.y + 1f, screenPos.z + 1f) / 2f;

// viewport => screen
screenPos = new Vector3(screenPos.x * Screen.width, screenPos.y * Screen.height, screenPos.z);