Trouble reading Motion Vectors in HDRP

Unity Engine
,
1

I set up a full screen Custom Post Process Volume to dump the depth and motion vectors info into a texture, but I keep getting zero values for the motion vectors.

I did activate “Motion Vectors” (and “Opaque Objects”) in the Renderer Asset (and in the “Frame” settings).

Also, in my CustomPostProcessVolumeComponent class I test if the camera is capable of computing motion vectors:

public override void Render(CommandBuffer cmd, HDCamera camera, RTHandle source, RTHandle destination)
    {
        m_ColorMaterial.SetTexture("_InputTexture", source);
        cmd.Blit(source.rt, colorRT, m_ColorMaterial);

        if (!camera.frameSettings.IsEnabled(FrameSettingsField.ObjectMotionVectors) ||
            !camera.frameSettings.IsEnabled(FrameSettingsField.OpaqueObjects))
        {
            Debug.LogError("Motion vectors not enabled for current camera");
            return;
        }

        if (!camera.frameSettings.IsEnabled(FrameSettingsField.DepthOfField))
        {
            Debug.LogError("Depth of field not enabled for current camera.");
            return;
        }

        m_DepthMotionMaterial.SetTexture("_InputTexture", source);
        cmd.Blit(source.rt, depthMotionRT, m_DepthMotionMaterial);
    }

The first Blit works like a charm and dumps the Color Texture correctly.

The second Blit dumps the correct depth values, but I keep getting (0,0) in my motion vector data.

And here is a snippet of my DepthMotion shader:

float4 FullScreenPass(Varyings varyings) : SV_Target
    {
        UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(varyings);

        float depth = LoadCameraDepth(varyings.positionCS.xy);
        depth = Linear01Depth(depth, _ZBufferParams);

        float2 motion = LOAD_TEXTURE2D_X_LOD(_CameraMotionVectorsTexture, varyings.positionCS.xy,0).rg;

        return float4(depth,motion.x, motion.y,1);
    }

What am I missing?

FYI, I’m using HDRP 10.5.0 and Unity 2020.3.9f1.

2

There is a bug. A PR have been considered to fix this:
https://github.com/Unity-Technologies/Graphics/pull/4714

3

Thanks for the info, do you know which version I can rollback to to make this work?

4

2019 and 2020 is fine. In 2020, you need to disable render graph from HDRP settings.

1 Like
5

Wow! Thanks!