orient particle to specific axis

DJM

i cant figure out how to orient an animated bilboard particle to a certain axis. it always plays the animation just like the sprite sheets orientation. any advice?

xyz

There's "angle" property in particle process material that lets you rotate the billboard in screen space.

DJM

hmm i want it to be a stretched billboard particle on a axis. u can set the angle but that keeps it flat projected to the camera

xyz

Not sure I fully understand what you want to do. The point of a billboard is to always face the camera. Maybe you meant some type of partial billboard that rotates around an arbitrary axis? What exactly you need it for, something like shotgun trails? Could you post an image that shows the effect?

DJM

in unity i could set the particle to "stretched bilboard" cant seem to find a similar function in godots particles

cybereality

I'm looking at the image, but I still don't understand the problem. What do you mean by "stretched"? Is that the scale of the sprite or of the velocity? A billboard always faces the camera, that is the whole idea, but you can make the velocity any direction you want.

xyz

I think I get what @DJM wants. One particle axis to be aligned with particle velocity vector while particle quad is rotated around that axis to face the camera as much as possible. Is that about it?

DJM

@xyz said: I think I get what @DJM wants. One particle axis to be aligned with particle velocity vector while particle quad is rotated around that axis to face the camera as much as possible. Is that about it?

yup

xyz

I'm not aware of a way to do it by clicking around gui. But it's relatively simple to make an intervention to a particle process shader. Convert the process material to a shader and at the end of vertex function simply set the TRANSFORM output matrix to have a desired basis.

float elongation = 5.0; #also can be sent as uniform
TRANSFORM[0].xyz = normalize(VELOCITY)* elongation;
TRANSFORM[1].xyz = normalize(cross(lookat, VELOCITY));
TRANSFORM[2].xyz = normalize(cross(TRANSFORM[1].xyz, VELOCITY));

lookat is a custom uniform you'll need to send to the shader. It's camera's look direction (basis.z) in global space

var cam = get_tree().get_root().get_camera()
var lookat = cam.global_transform.basis.z.normalized()
particles_node.process_material.set_shader_param("lookat", lookat )

A quick test:

DJM

tnx! looks exactly what i need

but im not sure how to implement that ive added a link to my particle sheet and a decal texture. could u do a small project that shows how to use this with raycast? i want to spawn the decal at the collision facing normal and emit 1 oneshot "stretched billboard" ,again, based on the hit normal of the raycast

https://drive.google.com/file/d/18IzZBECV1r8s-ngFbWpfv_MwhXyHj8yj/view?usp=sharing

xyz

Just send the hit normal to shader via another custom uniform and use it instead of VELOCITY vector.

DJM

@xyz said: Just send the hit normal to shader via another custom uniform and use it instead of VELOCITY vector.

will try it

xyz

Btw you don't need the whole particle system for a single billboard. You could simply instance a sprite and orient its basis using exactly the same approach.

DJM

@xyz said: Btw you don't need the whole particle system for a single billboard. You could simply instance a sprite and orient its basis using exactly the same approach.

im still going to try it, as i will need that functionality in other situations too

DJM

@xyz said: Just send the hit normal to shader via another custom uniform and use it instead of VELOCITY vector.

can u attach the the adjusted process material ? how do i make the custom uniform lookat?

xyz

Convert your particle process material to shader material (right click on the process material and click "convert to shader material". Then edit the shader code and add your uniforms declaration to the existing uniform block at the beginning of shader code:

uniform vec3 lookat;
uniform vec3 hitNormal;

DJM

ok shader compiled now tnx heres my setup i instatiate the decal from another script to be alligned with the hit normal. how do i get the forward(or wathever i need) of the instantiated node and send it to the shader correctly?

xyz

You simply send it the same way you're sending lookat:

particles.process_material.set_shader_param("hitNormal", raycastNormal)

where raycastNormal is the normal from the raycast, which I assumed you already have. If that spatial node is already aligned then it's probably its global_transform.basis.z.

DJM

i must be doing something wrong, cant get it to work

xyz

Why have you commented out setting lookat in the script? You need to send both of these vectors to the shader: camera look direction (lookat) and axis you want particle to be aligned with (hitNormal). Shader needs at least two vectors to figure out paricle basis.

Also "can't get it to work" doesn't mean anything. Remember - we need specific symptoms when debugging. What exactly happens?