Convert Curves to Grease Pencil?

Question

I'd like to know if there's a way/add-on to convert curves to Grease Pencil strokes? I know you can convert in the other direction, but I can't find anything to create Grease Pencil strokes from curves.

In attempting to setup guides for a model I'm working on, did so using curves. I'm now thinking GP would have been the better option, and would rather not have to recreate my guides.

Answer 1

First convert your curves in to mesh objects, AltC > Mesh from Curve/Meta/Surf/Text.

Now just copy and paste the script below into blender's text editor, then with your object still selected press Run Script.

This script below will draw grease pencil strokes on the active object.

import bpy
from mathutils import Vector

obj = bpy.context.object
mesh = obj.data
scene = bpy.context.scene

pencil = bpy.data.grease_pencil.new("pencil")
scene.grease_pencil = pencil

layer = pencil.layers.new("layer", set_active=True)
frame = layer.frames.new(scene.frame_current)

for edge in mesh.edges:
    stroke = frame.strokes.new()
    stroke.draw_mode = '3DSPACE'

    stroke.points.add(2)
    stroke.points[0].co = obj.matrix_world * Vector(mesh.vertices[edge.vertices[0]].co)
    stroke.points[1].co = obj.matrix_world * Vector(mesh.vertices[edge.vertices[1]].co)

Thanks to CoDEmanX for his making a grease pencil through bpy answer.

Answer 2

You may also fake a look of a Grease Pencil. Select your curve, go to the Shape panel in a curve data header, change the Fill type to Full. Increase the Depth value under Bevel: to give a curve some thickness. Give it a new material also and change its settings as pictured below. Now you have an editable imitation of a Grease Pencil.

Answer 3

As a follow-up to @David script, I noticed that it creates a new Grease Pencil Data every time the script is run. This can make it annoying if you simply want each mesh as a new GP layer in the existing data.

To instead make it create a new layer on the existing Grease Pencil Data:

import bpy
from mathutils import Vector

def convert_curve_to_gp(obj):

    #---- CHANGED ----
    scene = bpy.context.scene
    mesh = obj.data

    layer = scene.grease_pencil.layers.new("layer", set_active=True)
    frame = layer.frames.new(scene.frame_current)
    #---- /CHANGED ----

    mesh = obj.to_mesh(scene, apply_modifiers=False, settings='PREVIEW')
    for edge in mesh.edges:
        stroke = frame.strokes.new()
        stroke.draw_mode = '3DSPACE'
        stroke.points.add(2)
        stroke.points[0].co = obj.matrix_world * Vector(mesh.vertices[edge.vertices[0]].co)
        stroke.points[1].co = obj.matrix_world * Vector(mesh.vertices[edge.vertices[1]].co)

    bpy.data.meshes.remove(mesh)

obj = bpy.context.object
convert_curve_to_gp(obj)

Answer 4

If you like to do this procedurally, you can use Sverchok Add-On to access the existing Grease Pencil data block and then modify it on the fly using nodes. A quick example, below I have 3 curves joined and then I draw Grease Pencil using this node tree:

GIST: https://gist.github.com/cfa9cf5b707b909965e2b4956ad0ce25

This will potentially change as Grease Pencil is currently being developed into real object.