Hey,
I am trying to render a velocity map (including velocity of moving objects and velocity of camera).
Currently our pipeline is using a USceneCaptureComponentCube that implements the SceneCapturePixelShader.usf pixel shader:
IMPLEMENT_SHADER_TYPE(template<>, TSceneCapturePS<SCS_Velocity>, TEXT("/Engine/Private/SceneCapturePixelShader.usf"), TEXT("Main"), SF_Pixel);
Where SCS_Velocity is a new rendering mode I have added to SceneCapturePixelShader.usf:
#elif SOURCE_MODE_VELOCITY
FGBufferData GBufferData = GetGBufferData(Input.UV);
float2 camera_induced_velocity = CameraInducedVelocity(CalcSceneDepth(Input.UV), Input.UV);
float2 moving_objects_velocity = GBufferData.Velocity.xy;
OutColor = float4(moving_objects_velocity + camera_induced_velocity, 0, 0);
So, I’m trying to modify SceneCapturePixelShader.usf, such that the screen-space velocity is saved in OutColor.
But so far, I only managed to get the GBuffer velocity (after some hacks) which apparently only includes velocity of moving objects.
To get the pixel velocity due to camera motion, I tried using code from other shader:
float2 CameraInducedVelocity(float depth, float2 ViewportUV)
{
// Compute velocity due to camera motion.
float2 ScreenPos = 2 * float2(ViewportUV.x, 1 - ViewportUV.y) - 1;
float4 ThisClip = float4(ScreenPos, depth, 1);
float4 PrevClip = mul(ThisClip, View.ClipToPrevClip);
float2 PrevScreen = PrevClip.xy / PrevClip.w;
float2 Velocity = ScreenPos - PrevScreen;
return Velocity;
}
But this just returns zero.
Maybe View.ClipToPrevClip is always zero, because I’m using a USceneCaptureComponent?
I have read through numerous posts regarding calculation of motion vectors in UE4, but non of the suggested solutions seemed to work, in my particular case.
You are my only hope…