Setting in-built curve properties via Scripting

Coding Python Support
1

It is probably (definitely) easier to do this via the Graph Editor but please bear in mind that I am starting out learning Python in Blender so it could end up being just a valuable learning experience rather than a better way of doing things.

I am trying to write a script that will create a cube and add a built in modifier - the default in the Graph Editor is a sine curve. The code below does that. However, I would like to change the Amplitude, Phase Multiplier, Phase Offset and Value Offset. And maybe even the curve type to something else - it would be good to know how.

Standard approach so far has been to copy code from the Info window and try in the Console. When I alter Amplitude in the Graph Editor, for example, the code generated is:

bpy.data.actions[ā€œCubeAction.008ā€].(null) = 10

This throws up a syntax error because .(null) is invalid when used in Console. Looking at the available options (by pressing TAB after ā€œ].ā€ hasnā€™t helped.

Incidentally, it doesnā€™t matter what property I change in the Graph Editor, the .(null) thing pops up for all of them in the Info window which is very odd.

Iā€™ve tried using several options. Iā€™ve tried putting that line after the ui_type change in the Text Editor just incase it was down to a context error but that did not work.

After two hours and several cups of tea Iā€™ve come to you chaps for help :slight_smile:

#090522
#Creates cube, adds keyframe, changes ui.type to add built in sine curve in graph editor
import bpy

bpy.ops.mesh.primitive_cube_add(size=2, enter_editmode=False, align=ā€˜WORLDā€™, location=(0, 0, 0), scale=(1, 1, 1))

mycube = bpy.data.objects[0]

mycube.keyframe_insert(data_path = ā€œlocationā€, frame = 1)

bpy.context.area.ui_type = ā€˜FCURVESā€™
bpy.ops.graph.fmodifier_add(type=ā€˜FNGENERATORā€™, only_active=True)
bpy.context.area.ui_type = ā€˜TEXT_EDITORā€™

PS:
I have been messing with the following line from sozap who helped with an answer to an earlier question. But Iā€™m not making progress not matter how I modify it
bpy.context.selected_objects[0].animation_data.action.fcurves[0].data_path

2

funky_sin
funky_sin1425Ɨ850 171 KB

I tried adding (via scripting) a vertical sinusoidal motion to each object with a phase offset so they kind of ripple around the edge of a circle. The idea being that this is scalable and easily modified in terms of just tiny alterations in the code (eg number of objects). Nearly had it: except that the interpolation type makes the sin wave really funky (see image). So: I need help!!! :slight_smile: I cannot code the alteration of the interpolation type and I have made no progress with the question above. I know it is two questions - the answer to just one would be COOOOOOL.

3

Not an excessive amount of commenting in this but it should point you in the right direction for your original post.

import bpy


# just for flexibility
def add_item(item_type="primitive_cube_add"):
    primitives = ["primitive_plane_add",
        "primitive_cube_add",
        "primitive_circle_add",
        "primitive_uv_sphere_add",
        "primitive_ico_sphere_add",
        "primitive_cylinder_add",
        "primitive_cone_add",
        "primitive_torus_add",
        "primitive_monkey_add",
        ]
    if item_type not in primitives:
        return {'CANCELLED'}
    eval(f"bpy.ops.mesh.{item_type}()")
    return bpy.context.object

# add a primitive and store a reference in my_obj
my_obj = add_item("primitive_uv_sphere_add")

# insert a keyframe
my_obj.keyframe_insert(data_path = "location", frame = 1)

# convenience variable
fcs = my_obj.animation_data.action.fcurves

x_axis = fcs[0]
y_axis = fcs[1]
z_axis = fcs[2]

# add a modifier to x axis
my_mod1 = x_axis.modifiers.new(type='FNGENERATOR')

# modify the amplitude of the function
my_mod1.amplitude = 5
1 Like
4

GENIUS!!! Thank you so much. Now I can do exactly what I want! Although I am going to take some time to properly understand rather than just copy - but itā€™s perfect.

I have just one question - how did you learn or find out how to do this?

5

1st recommendation:
Get only visible details and properties of a node in python - Coding / Python Support - Blender Artists Community

Enabling feedback to show what the python commands are for most items (in your specific example this got you to the:

bpy.data.actions[ā€œCubeAction.008ā€].(null) point of the code.

2nd recommendation:
Just spending time using commands in the console.
since you know your keyframe is an fcurve try to find it in the object data block

3rd recommendation:
Continue to search and post on forums. Given Blendersā€™s increasing user base; someone somewhere is bound to have either stumbled there way through it previously, or just be too stubborn a person to not know themselves and fumble through an answer.

2 Likes
6

I know this is a really old thread, but Iā€™m a bit confused by this line of code. I thought eval() just returned a string in python. What is it doing here if the resulting string isnā€™t assigned to anything?

7

if you hit ā€œeval(ā€ in the console and the TAB you will get:

image
image872Ɨ256 86.8 KB

it just executes the command which you generated by the string.

more info: https://www.programiz.com/python-programming/methods/built-in/eval

hope that helps

1 Like
8

Thanks for getting back to me so quickly! So Iā€™m guessing the reason you chose to execute the code this way is because you can use the flexibility of f-strings to format your code?

9

i guess thatā€™s why he did it that way. :wink:

1 Like