paulfe
Hello
I would like to get as an attribute the light received on a geometry.
Is it possible?
I could achieve it by getting Cd attribute using a texture that was previously baked with the light. However that would be a more tedious and less flexible process.

paulfe
Hello
I would like to get as an attribute the light received on a geometry.
Is it possible?
I could achieve it by getting Cd attribute using a texture that was previously baked with the light. However that would be a more tedious and less flexible process.

jsmack
You could do as others have done and write a renderer in SOPs using VEX.

protozoan
If "simplistic" lighting is enough (like: find out what's approximately in the shadow of a directional light or a point light) you can look at the mask by feature SOP. This won't do "real" lighting though.

Andy_23
What would you do with that attribute? Jsmack and Martin's suggestions are all valid. Yet we don't know what you want out of it.
I'm curious.

• Raycast each point towards the camera and towards the light.
  
• Remove the points if any of their rays intersect with your mesh.
  
• 

Map the angle between point normals and light directions to radii.
  
• Project the points on a plane perpendicular to the camera.
  
• Rotate the plane points to the Z-axis.
  

// PARAMETERS
string cam = chs('camera');
string light = chs('light');
float radius_min = chf('min_radius');
float radius_max = chf('max_radius');

// POSITIONS
matrix xform_cam = optransform(cam);
matrix xform_light = optransform(light);
vector pos_center = getbbox_center(0);
vector pos_cam = cracktransform(0,0,0,0,0, xform_cam);
vector pos_light = cracktransform(0,0,0,0,0, xform_light);
vector pos_srf = v@P + v@N * 1e-3;

// DIRECTIONS
vector dir_cam = normalize(pos_cam - pos_srf);
vector dir_light = normalize(pos_light - pos_srf);
vector dir_center_cam = normalize(pos_cam - pos_center);

// RADIUS
float angle = max(dot(normalize(dir_light), v@N), 0.0);
float radius = chramp('radius', angle) * radius_max;

// RAYCASTING
int prim_cam = intersect(0, pos_srf, dir_cam, set(0), set(0));
int prim_light = intersect(0, pos_srf, dir_light, set(0), set(0));
int prim_max = max(prim_cam, prim_light);
if(prim_max >= 0) removepoint(0, i@ptnum, 1);

// ORIENTATION
vector dir_perp = cross(dir_center_cam, dir_cam);
vector pos_plane = cross(dir_center_cam, dir_perp) + pos_center;
matrix3 m_rot = maketransform(dir_center_cam, {0,1,0});
pos_plane *= invert(m_rot);

// ATTRIBUTES
v@P = pos_plane;
v@N = {0,0,1};
v@up = {0,1,0};
f@mask = angle;
f@pscale = radius;

paulfe
I am experimenting turning 3D objects into vectorial 2D for a plotter machine.

protozoan
Now that's something you don't see often, interesting!