Saturday, August 12, 2017

Scoring a movie with supercollider, blender, python and osc - part II: keyframing and animation curves

Problem?



In the previous part of this tutorial, I described a way to insert markers on blender's timeline, and to use blender's python scripting abilities to convert these markers into OSC messages which then can be interpreted in supercollider to perform commands (e.g. start and stop patterns or sound effects). This approach works very well for sending discrete commands: things like start this, stop that. If you haven't read that part yet, please go read it as you will need to understand the concepts explained there to follow part II.

In this blog post, I want to show how one can use blender's powerful keyframing system with animation curves to continuously update parameters in supercollider sketches. This technique adds extra possibilities for driving supercollider from blender.

Approach?

In the blender scene, I will add custom properties, and animate those via keyframes and animation curves. I will extend the python script I developed in part I to send the parameter value updates to supercollider.

What is a keyframe?

A keyframe represents the value (the state) of one or more parameters at a moment in time. Suppose you have an X-position of an object in a 3d scene. At time frame=0 you can set X=0 and insert a keyframe on frame=0. At time frame=100, you can set X=10 and insert a new keyframe on frame=100. Now for frames between 0 and 100, the value of x can smoothly vary between 0 and 10, that is, the values of x can be interpolated between the keyframes (you can also ask the system for an abrupt change instead of interpolation). The interpolation can be linear, or can include "easing".

Adding custom properties

Blender is extremely keyframeable. Literally every parameter you see in the UI can be keyframed. Blender is also very extensible: users can add new parameters ("custom properties") in the UI. And those new parameters can be keyframed. 
To add a custom property, first switch to blender's default view


Then, on the right hand side, go to the scene tab, and in the custom properties section, click the Add button.


As we did in part I of the tutorial, we will again use a naming convention for the properties so that our python script knows what to send to supercollider from the property name. The proposed naming convention is that a property named SC_something42 wil be sent to supercollider as osc command /something42 with as argument the property value. We will make the python script so that only changes in values are sent. Values that don't change from one frame to the next will not be resent to supercollider. The intention is to avoid creating an avalanche of useless OSC messages.


After clicking the add button, we can set up our property using the naming convention. Suppose I want to automate a frequency in some synth. A possible custom propertyname could be SC_animfreq. This would trigger sending an OSC message /animfreq to supercollider with the value of animfreq as argument. I've set the default value to 440, and the min and max to 20 and 20000 respectively.


Now on the blender timeline, navigate the playhead to - say - frame number 10 (the easiest way is to type 10 in the current frame edit box), set the value of customproperty animfreq to - say - 220. Hover your mouse cursor over the value 220 of animfreq and press the letter "i" (for "i"nsert keyframe). The edit box with value 220 should change color to indicate that a keyframe has been inserted for the custom property.


Next, move the playhead to - say - frame 100, change the value of the custom property to 880, hover the mouse cursor over the 880 and "i"nsert another keyframe.


Now as you drag the playhead between frames 10 and 100, watch the custom property value box. You should see the number change gradually. This is the linear interpolation that happens between keyframes by default.

If we want to alter this behavior of linear interpolation, we need to switch to the "graph editor". A full explanation of everything that an be done in the graph editor falls outside the scope of this blog post (i.e. you'll need to find some blender tutorials about the graph editor on youtube if you want to dive deeper - let's just say that you can do some funky stuff).


After some zooming in x and y direction you can see the linear interpolation drawn as a curve.


By pressing "T" while hovering the mouse cursor over the graph area you can change the interpolation type. Since we're animating a frequency, it makes sense to set the interpolation type to exponential. Be sure to look for tutorials on F-curve modifiers to see some fancy stuff that is possible with the curves. For the purpose of this tutorial we won't go any deeper.


So far we have added an animated custom property. Now let's tell blender to send it to supercollider in the form of OSC messages. To do so I will extend the python script developed in part I of the tutorial. The additions with respect to part I are marked in the figure.



The OSC messages can be received in supercollider in exactly the same way as in part I. The received values then e.g. can be used to set the freq argument in a synth (or the density in some cloud of sound grains, or whatever you feel like doing).

A blender file and supercollider file with a simple demonstration can be downloaded from google drive.




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