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Question _CameraMotionVectorsTexture meaning/definition

Discussion in 'Shaders' started by alien13mars, Nov 23, 2022.

  1. alien13mars


    Nov 2, 2022
    Hey, does anyone know how exactly _CameraMotionVectorsTexture is defined?
    If I do
    Code (CSharp):
    1. tex2D(_CameraMotionVectorsTexture,In.uv);
    which channel decodes the motion in x-direction? Which for the y-direction?
    In which range are the numbers decoded?

    From my experiments I determined the following:
    - g-channel decode movement in x-direction
    - r-channel decodes movement in y-direction
    - they numbers probably range from -1 to 1 for each direction. However, they are very small! Without scaling them by a factor of at least 1000 they are bascially useless.

    Are those oberservation correct?
  2. bgolus


    Dec 7, 2012
    AFAIK the built in rendering path stores the values as:
    red channel = x direction in screen UV space.
    green channel = y direction in screen UV space.
    This means a value of 1.0 (or -1.0) in either means the object moved the width or height of the screen between the previous frame and current frame.

    The SRPs appear to use the same rg = xy, but stored so you have to do rg * 2.0 - 1.0 to get the UV range, and clamped to be between -1.0 and 1.0 after decoding, where as the built in pipeline doesn't clamp the values.
    alien13mars likes this.
  3. alien13mars


    Nov 2, 2022
    Thank you for your answer! This clears it up for me!