Velocity function

[Ahleroy]

I am not sure to understand the content of this custom function.
Would you mind giving an explanation ?

float2 Velocity = inVelocity.xy;
if(Velocity.x > 0.0){
const float InvDiv = 1.0f / (0.499f * 0.5f);
	
Velocity = Velocity * InvDiv - 32767.0f / 65535.0f * InvDiv;
}
else {
float4 ThisClip = float4( inUV, ConvertToDeviceZ(inDepth), 1 );
	float4 PrevClip = mul( ThisClip, View.ClipToPrevClip );
	float2 PrevScreen = PrevClip.xy / PrevClip.w;
	Velocity = inUV - PrevScreen;
}

return Velocity * 100;

Thanks.

[ProfFan]

Unreal does not calculate the velocity of static objects, so you need to interpolate using camera transform :)

[el3ment]

Should you be testing PrevClip.w to ensure it is positive?

[ProfFan]

Why?

[ywu40]

Hello,

Which file includes the above mentioned velocity code? I searched in all source code files and project, I did not find the code

Thanks

[ProfFan]

@ywu40 It is in a UE4 material shader, you need to open it in UE4's Blueprint view.

[ywu40]

@ProfFan Thanks. I found it now.

[ywu40]

@ProfFan One more question, I saw the return value code "return Velocity * 100;". May I know why do you multiply 100? What is the meaning of 100 here? How/where do you get the value 100? Is it the value of Field of View?

Thanks for your help.

[ProfFan]

@ywu40 From what I remember it is arbitrary (as the original value is too small). You can also do a log or so to increase the dynamic range

[ywu40]

@ProfFan Thanks very much for the quick response. So multiply 100 is just for better visualization, the actual value should be just "Velocity" itself, right?

[ProfFan]

Yes