Rendering only points that are facing camera

[zjie]

Hi guys, I am rendering points scatter on a geometry but is there a way to render only the points that are facing the camera? So as to prevent xray of the inside or the other side of the geometry. Or maybe it can be like a ramp, where the points near the camera is white, ramping to black at the other side, and multiply it to the pscale. 

 

 

 

pointsFacingCamera.hip

 

Edited October 17, 2019 by zjie

[StepbyStepVFX]

Hey, the simplest solution I see is to tag the faces that have normal direction away from the camera, and make the scattered points inherit that attribute / group, to delete these points later.

You can compute a vector that goes from the position of the face toward camera position, and calculate the dot product between this vector and the normal of the face : if positive it is facing the camera, if negative it is oriented away, and you can tag the face.

Use a primitive Wrangle to do that.

Then scatter the points, let them inherit the proper attribute or group, and delete the ones that were spawn on the faces looking away.

Edited October 17, 2019 by StepbyStepVFX

[StepbyStepVFX]

Another solution if you just have a point cloud with no geometry on which points are scattered :

http://www.weizmann.ac.il/math/ronen/sites/math.ronen/files/uploads/katz_tal_basri_-_direct_visibility_of_point_sets.pdf

The algo is quite easy to implement.

[ThomasPara]

You need to ray each point through your original mesh, and see if that occludes. Because you can have normals pointing towards you that are occluded.

pigray.hip

[StepbyStepVFX]

You will have a nice video. And I am pretty sure I saw another one, probably from Entagma, but can't find it on Google, nor Patreon.