Calculate velocity in screen space

[sipi]

How would you calculate the velocity of a moving geometry (consistent topology, static camera) in screen space?

[haggi]

You have a vex function called toNDC where you can use your velocity information to transform it to normalized raster coordinates. Even if it says it's only well defined in shading context it seems to work in sop as well.

[sipi]

15 minutes ago, haggi said:

You have a vex function called toNDC where you can use your velocity information to transform it to normalized raster coordinates. Even if it says it's only well defined in shading context it seems to work in sop as well.

yeah, i guess i have to do something with the NDC stuff, but not clear to me how

Edited Thursday at 03:15 PM by sipi

[Librarian]

@sipi maybe
 

//box ndc
vector offset = {0.5, 0.5, 0};
vector cameraScale = set(ch("camera_X"), ch("camera_Y"), 1);
if (@group_near)  @P = set(@P.x, @P.y, ch("near")*-1); 
if (!@group_near) @P = set(@P.x, @P.y, ch("far")*-1);  
vector xformpos = @P *  maketransform(0,0, offset,{0,0,0},cameraScale,{0,0,0}); 
@P = fromNDC(chs("camera_path"), xformpos); 

 

Edited Thursday at 09:27 PM by Librarian

[sipi]

This is what I could come up with. Uses 1 qLib node (Camera Plane ql).

screen_space_velocity.hiplc

Edited Thursday at 09:38 PM by sipi
typo