WEBVTT

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Hello and welcome to Scripting for Artists. My name is Sybren.

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And in this episode, we're going to take a look at Custom Properties.

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In the last video, we created a panel

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and add existing properties to it. And this is already quite powerful.

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If that is enough for your situation, then please

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don't make it any more complex. Simpler is often better.

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However, there are these situations though

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where you want to attach your own data to things in Blender.

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To start, let's take a look at the kind of Properties there are.

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Throughout the series, you've seen existing Properties

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like "object.location" or "context.scene".

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Then, there are the Custom Properties that you can create

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in the Custom Properties panel. Maybe you've also seen these properties

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where the Edit button is gone and where it says API Define,

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and this means it's been defined from Python.

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This is what we're also going to look at in this video.

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To give us a concrete goal to work toward, will be creating

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a Mass OBJ Importer. Each scene will get a property that contains

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the path of a folder, that contains its OBJ files. And then,

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we'll create an operator that loads all the OBJ files from that folder.

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And finally,  we'll look into creating an operator

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that reloads those OBJ files from disk. So in that way,

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you can have a one-button reload of all your OBJ files.

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This is quite a bit of work. So let's get started. For this episode,

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we're going to create a new Addon and I've started already.

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I've added a new Python file. I've installed it

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as an Addon, load it in my Editor, which is a Visual Studio code.

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I will quickly race through this

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because you've seen all of these before in the previous videos.

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If you haven't seen this yet, please take a look at the videos

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about creating your own Addon and creating User Interfaces.

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So we start with the BL Info Dictionary. I've set the name

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to the Addon to Scripting for Artists "Mass importer".

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The rest of the information is pretty much as you would expect,

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"import bpy", of course, is next. Then, I want to have everything

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that we're going to do available to us in a panel there.

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We can show the buttons, we can show the properties,

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we can do everything we want. I've created a new panel by copying

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the code we had for a monkey grid and then adjusting it.

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So it's pretty the same, except that it has the label "mass import",

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and that is also reflected in the class name.

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It's now called "view 3D PT mass import"

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We're going to draw something, but not just yet. Then, of course,

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we have the Register and Unregister functions.

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Those are necessary for any Addon. We're going to add more classes to this file.

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So we'll have an operator for doing the mass import.

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Then we also will have an operator for doing

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a single re-import of an object, and then also an operator for doing

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a mass re-import of all the imported objects.

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So we're going to have more. And I didn't want to copy paste

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the "bpy.utils.unregister class", and then make sure that

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in the unregistered, is also copied to the unregister class,

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and managing all of that. So instead of that, I've created a list

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called Blender Classes, in which I have only the panel

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that we have now. And then, in the Register and Unregister,

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we loop over it with a Forloop. So for Blender Class and Blender Classes

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will go over this list. And for every item in that list,

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it will call "bpy.utils.register class" or "unregister class"

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and this makes it a little bit easier to add new stuff later,

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because new classes, we can just add to this list.

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Now that our code is really simple, let's see that

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it actually works in Blender, so that we can be sure that

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when we start adding stuff, we added on a basis that actually works.

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So in the User Preferences, enable the Addon. And then here,

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in our Monkeys tab, we can see our Mass Import panel.

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Of course, it's nothing drawn yet, but that is what we expected.

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So on the basis for our code, the registering and the unregistering

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in the existence of the panel itself, that's all correct.

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Okay. So let's start creating these properties that we wanted to have.

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This is quite simple actually.

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You know that there's a lot of stuff in "bpy.types",

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and we want to have a property on the scene that contains

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the import path of the OBJ files that we want to have.

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So we start with "bpy.types.Scene", with a capital Scene,

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"." and then the name of our property.

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Let's call it "Mass import path". Now, it's very similar

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to adding your own properties to your own operator,
except that,

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with the operator we had class we could use

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to declare the properties, and now, that class is already there,

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so we cannot add anything to it. So it's a little bit different.

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So, instead of using the ":",

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we use the "=" sign, and then again, we assign property.

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They'll even be a path of props, and a file path or a directory path

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is just a String.

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So that gives us a String Property. Now for the User Interface,

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we may want to give it a nice name. So let's call it "obj folder",

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and they always end up with a ",",

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because then, I can add stuff on the next line without having

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to go back up and add that "," again. This is valid Python,

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it makes your changes a bit more localized. You can now add

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other stuff here without changing the line above.

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This is in the Register function, so there, we add a property,

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of course, we have to delete it again in the Unregister

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to clean up what we did.

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Then basically, you take this and you say "del" that property.

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And that tells Python, just delete the thing. And this is enough.

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Let's see how this looks in Blender.

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Here, we have to reload our code. In Blender 2.83 and newer,

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can do that here with Reload Scripts. If you've an older version of Blender,

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press F3,

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then type"reload scripts". They both do the same thing.

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Except, through the menu, you can add it to the quick menu,

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when you press Q. And this is the approach that I will use

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from now on. So we've reloaded our code.

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Let's take a look at the scene.

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There you go. We have our own property "Mass import path".

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The default is empty because we haven't set any default,

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and it's just there, and every scene will have it.

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We can also change the property from Python. Keep your eyes

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on the Custom Properties panel here, which is in the Scene tab.

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Take a look at that, what happens when I actually assign a value.

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You have to work with your mouse a little bit to make it redraw.

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But you can see that, now, with that, we've assigned a value to it.

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It is actually stored in the Custom Properties.

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It's API defined, which means that you cannot just delete it.

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And this is one of the major advantages of using
your Properties like this,

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instead of just clicking the Add button here

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and creating a new one. When you create it through Python,

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you can be sure that the property is there.

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Even if it hasn't been set, it will have a default.
So it's one less thing to worry about.

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The other advantage is that, we can set Subtypes.

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And this will indicate to Blender

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what kind of String we're talking about. So this is going to be a path,

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and it would be nice if it had like a little button that

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you could have a file browser that selects the path for you,

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instead of having to type it in the Python console.

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All of this is done by Blender once you've set the Subtype correctly.

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Let's do that. The Subtype is set

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by the Subtype parameter, and then you pass a string

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that indicates a Subtype. In order to find the Subtypes for a specific property,

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you can go back to Blender, Help,

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Python, API Reference, and search for "bpy.props.string property"

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and there it will tell you which subtype there are.

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In our case, it's a Directory Path or "Dir Path".

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Now, let's reload the code and see what happens here

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in this corner of the Interface.

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There you go. It has a button to browse, and you can select directories.

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Because I set it to a silly value,

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it'll just start at a silly directory, because it's not a valid path.

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But if I change this to "//" which indicates

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the current directory of the Blend file,

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it will open it here, and I can navigate to my OBJ files directory,

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click "accept" and then it has set here the path.

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That is exactly what we wanted, except that we want this behavior

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in our own panel, of course. Let's do that. In our Panel code,

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we can remove the pass because we actually going to do something

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and let's start with getting the layout.

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We didn't do this before, but do know that every "self.(something)"

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we'll do a little dance to see, is it defined on this class,

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if not, look at a parent, is it defined there,

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if not, look at the grandparent etc.. So we're saying

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"layout = self.layout" ,  we only do this dance once,

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and then just use the layout object. Let's add a Column,

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and then add the Property. The Property was defined on the scene,

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which is "context.scene". And the property name was

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"mass import path". That's it.

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Reload the code, and there we have our Property browse button.

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Now, let's go and create an operator that import all the OBJ files

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from that directory. And I want to name it quite similar

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to the operator that already exists for importing OBJ files.

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So let's take a look at that. That is "bpy.ops.import_scene.obj"

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so let's call our operator

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"import scene.obj mass". So here, we have an empty operator,

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you've seen this before, I just named these differently,

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called "imports scene.obj mass" and it has an Execute function.

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I put in this little comment as a reference, and then it called

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"self.report". This takes a report type which can be

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info or warning or error, and then a string that is unreported.

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It returns "cancelled" because nothing is done yet.

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Again, I'm taking small steps. I first make sure that your printer is there,

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and that it registered properly. Then we can add it to a panel,

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we can click on the button, we can see that it works

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before adding more complexities to it. So the operator is here.

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Now, I copied this name, I go to the Blender classes list,

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I added the name to the list and that takes care of the Registering

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and the unregistering. So what is left now is add it to the panel.

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So all we need is the "BL ID name". Paste it in, save in Blender,

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reload the script. And we have a button, we click on it.

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It says "no code to load from / /", which is the error we expected.

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Now the next step is, finding the OBJ files,

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and importing them. And afterwards, we want to be able

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to re-import them. So we have to keep track of

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which object was imported from which file. The best way to do that is

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to add another property to the ObjectTtype. So let's do that now

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before we start importing them. Here, in a Register function,

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we're going to do the same thing as we did to a scene,

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but then to an object.

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And then, it also becomes a String Property,

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but then with OBJ file, instead of OBJ folder. So the folder

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and the file name combined will give us the final path of the OBJ file.

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Because there is no subtype for just a file name,

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it's only for a full file path or a full directory path.

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Will just keep this as a String and don't define any subtype.

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So before we look at the importing, that's add this property to the panel.

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We have the Panel code here, let's create a new column for this.

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And there, we have the Property. But remember "context.object"

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can be none, so we have to add a little guard around this.

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None is considered false with Python, and real objects is considered true.

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So if "context.object" will evaluate to "true",

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it's real object, and then draw the property. It will evaluate to "false"

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if there is no active object, and then it will draw the label instead.

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Let's give it a try.

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And there, we have our property, and we can set it "per objects",

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as you can see.

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Now let's build the importing itself. So here we are,

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at our Mass Importer operator. Let's write a little layout

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of what it is supposed to do. It has to find the object files,

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and for each file,

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import it,

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and record its file name in the Object Property.
Let's look at that first steps,

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this is going to take a few steps actually.

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Because for finding files, we have to use Python functionality.

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And Python doesn't understand the Blender specific "//" meaning

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of relative to the current Blend file.

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So we have to convert it to something that Python understands,

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then use that to find the OBJ files, then convert it back

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to something Blender understands, and import the files.

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First of all, we have to turn that "//" into something absolute,

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and this is done through a function in "bpy.path.abspath"

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"bpy.path.abspath(context.scene.mass_import_path"

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will give us the absolute path of the file that we want to import.

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We can check this by reporting this in our error message.

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Just pause the video, give this a try, and then come back here.

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Now, we have to convert this to a path object

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from Python's Path Lib Library.

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And then, we can use this import path variable to find all the OBJ files,

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and loop over them in one go, like this.

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This will find everything that matches "*.obj",

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so files or directories ending in that "obj".

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From now on, I'll assume that you won't create
any subdirectory called

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"(something).obj", and that everything is an actual OBJ file we import.

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Now, all we have to do is import it.

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In Blender,

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go to the OBJ Importer and press Ctrl C, and then,

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you can Ctrl  V, Code.

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This converts that Path Object we have back into a String,

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so that Blender understands it.

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And then, this whole line will import the OBJ file.

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So now, we have covered that for each file imported,

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the only thing that's left is recording its filename.

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Part of the working of this Import Operator is that

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it deselects everything and then it selects the objects that are imported.

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This means that we can loop over all selected objects

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and then assign our Custom Property to them.

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This is why I like the Path Lib Object so much.

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It's quite simple to work with if you just want to have

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the filename component of a path, you can just do the "path.name".

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If you want to have the drive object, you do ".drive"

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and is a very object oriented approach to Paths, and I quite like that.

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Now we're importing. We record the file name where it came from.

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So this should be it.....let's give it a try.

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I'll throw out the existing objects,

00:15:08.600 --> 00:15:10.240
browse to my OBJ files directory,

00:15:11.720 --> 00:15:15.000
and then Mass Import everything, and there we are. The files are imported.

00:15:15.000 --> 00:15:18.120
They're all at the origin, and each of them

00:15:18.120 --> 00:15:22.720
has the OBJ filename set to whichever they came from.

00:15:22.720 --> 00:15:25.840
Now, all that's left for us is to make an operator that reloads the OBJ file.

00:15:25.840 --> 00:15:29.080
To keep it simple, let's not do this on mass,

00:15:29.080 --> 00:15:31.480
just reload the active object. That means deleting the object from the scene

00:15:31.480 --> 00:15:34.720
and then loading it again from the OBJ file.

00:15:34.720 --> 00:15:36.960
Of course, before we deleted from the scene, we have to make sure that

00:15:36.960 --> 00:15:39.720
we stored the transform of the object, so that

00:15:39.720 --> 00:15:42.720
when we reload it, it can be restored. So that it's positioned in the same way

00:15:42.720 --> 00:15:46.360
as it was before we reloaded it.

00:15:46.360 --> 00:15:47.360
Let's start with a new operator.

00:15:50.080 --> 00:15:53.600
Let's call it "obj reload". Here, I select some text,

00:15:53.600 --> 00:15:57.080
press Ctrl D and that will select next occurrence of that text.

00:15:57.080 --> 00:16:00.600
Then, I can just type Reload, and both the class name and the ID name

00:16:00.600 --> 00:16:03.120
we'll change to "obj reload".

00:16:04.480 --> 00:16:08.360
Let's say "reload mass imported obj", and then we can write

00:16:08.360 --> 00:16:11.960
the Execute function. For this code, I will assume that every OBJ

00:16:11.960 --> 00:16:15.360
has one object in it. You can extend the code so that it can handle

00:16:15.360 --> 00:16:18.600
multiple objects for OBJ. But let's keep it simple for now.

00:16:18.600 --> 00:16:21.600
We're going to refer to the active object quite a few times,

00:16:21.600 --> 00:16:24.000
so let's make life simple for us.

00:16:25.960 --> 00:16:28.600
Just call it "ob", let's make a little overview for ourselves again.

00:16:28.600 --> 00:16:30.840
First, we have to store

00:16:32.000 --> 00:16:33.480
what we want to remember.

00:16:35.080 --> 00:16:36.600
Remove the object from the scene,

00:16:37.600 --> 00:16:38.840
load the OBJ file,

00:16:40.080 --> 00:16:44.480
and restore what we remembered. Loading the OBJ file

00:16:44.480 --> 00:16:47.360
will not automatically set our Custom Property.

00:16:47.360 --> 00:16:50.600
In the end, that's what we want to restore. And we want to be able to restore

00:16:50.600 --> 00:16:51.840
the transform as well.

00:16:55.080 --> 00:16:56.480
Let's remember the file name.

00:16:59.600 --> 00:17:03.080
And let's take a copy of the Matrix. If I wouldn't make

00:17:03.080 --> 00:17:06.840
a copy of the Matrix, then the variable Matrix World

00:17:06.840 --> 00:17:10.080
would be a reference to the Object Matrix. And if we delete the object,

00:17:10.080 --> 00:17:13.480
that reference won't be valid anymore,

00:17:13.480 --> 00:17:14.840
you can get all kinds of weird results.

00:17:16.080 --> 00:17:18.240
Now, removing the object from the scene actually means

00:17:18.240 --> 00:17:21.600
removing the object from all the collections that it's in.

00:17:21.600 --> 00:17:24.960
Fortunately, Blender gives us a list of all those collections.

00:17:33.960 --> 00:17:37.600
This will unlink the object from all the collections.

00:17:37.600 --> 00:17:40.600
The problem is that, of course, as soon as we unlink the object

00:17:40.600 --> 00:17:43.080
from the first collection, this thing that we're looping over

00:17:43.080 --> 00:17:46.000
will change. Changing something while you're looping over it

00:17:46.000 --> 00:17:50.240
is never a good idea. We can do this, "list(ob.user_collections)"

00:17:50.240 --> 00:17:54.480
and this will create a new list for us.

00:17:54.480 --> 00:17:57.840
That new list is a copy, so it won't be altered by removing the objects

00:17:57.840 --> 00:18:01.600
from those collections, making this for loop safe.

00:18:01.600 --> 00:18:04.120
If you want, you can also remove the object from "bpy.data" now,

00:18:04.120 --> 00:18:07.960
but this is only safe if it's not referenced from anything else.

00:18:07.960 --> 00:18:10.840
Again, Blender to the rescue.

00:18:14.840 --> 00:18:18.360
"ob.users" will give us that user count.

00:18:18.360 --> 00:18:22.480
 And that is that tiny little square you see also with Materials and Meshes,

00:18:22.480 --> 00:18:25.000
when you use them in different places throughout the Blend file.

00:18:25.000 --> 00:18:28.960
If this number is 0, that means that the object is no longer used,

00:18:28.960 --> 00:18:31.720
and we can actually remove it from Blender's memory.

00:18:35.720 --> 00:18:39.960
From this point on, we can no longer refer to "ob",

00:18:39.960 --> 00:18:44.000
because it's been removed from Blender.

00:18:44.000 --> 00:18:45.720
So to prevent this from ever using it again,

00:18:46.960 --> 00:18:50.600
I just say "del ob". This removes the "ob" name from Python's memory.

00:18:50.600 --> 00:18:56.360
That means that, if I say "ob.location" here,

00:18:56.360 --> 00:18:58.720
Python will scream at us, because it doesn't know

00:18:58.720 --> 00:19:03.080
what "ob" means anymore after this line.
 It's just a little bit of security for ourselves

00:19:03.080 --> 00:19:05.600
so that we don't use something

00:19:05.600 --> 00:19:09.120
that's no longer valid. Now. We need to load the OBJ file again

00:19:09.120 --> 00:19:11.480
which we've done before. So let's take a look at that code.

00:19:11.480 --> 00:19:15.600
We have to do this trick again, and then we have to do this line

00:19:15.600 --> 00:19:19.240
for just that one object. So let's put this into a function

00:19:19.240 --> 00:19:21.720
which we can call from both places.

00:19:35.360 --> 00:19:39.080
Here, I've created a new function that takes a scene,

00:19:39.080 --> 00:19:42.720
and this means that it will return a "path lib.path".

00:19:42.720 --> 00:19:45.360
I like this notation quite a lot, because then, you can see

00:19:45.360 --> 00:19:48.240
what something returns without having to dive in the code

00:19:48.240 --> 00:19:51.240
and see what happens. This is not something that will be checked at Python,

00:19:51.240 --> 00:19:54.120
so it's up to you to actually live up to your work.

00:19:54.120 --> 00:19:56.960
This code is now pretty much the same as this

00:19:56.960 --> 00:20:00.960
and it returns the new Path Object. That means that
we can remove this line,

00:20:00.960 --> 00:20:04.120
and we can just do "mass_import_path(context.scene)" here.

00:20:05.360 --> 00:20:09.360
I specifically pass this scene

00:20:09.360 --> 00:20:13.080
and not the context. Have to fix a little mistake here.

00:20:14.000 --> 00:20:18.000
I explicitly passed the scene and not the entire context.

00:20:18.000 --> 00:20:21.000
It would have worked fine if we were to pass the context,

00:20:21.000 --> 00:20:24.120
but then, you wouldn't be able to see which part of the context

00:20:24.120 --> 00:20:26.960
was actually used by this function. This is why I wanted

00:20:26.960 --> 00:20:30.080
to pass a scene itself and not the context.

00:20:30.080 --> 00:20:33.480
Of course, we could have also passed "context.scene(mass import path)",

00:20:33.480 --> 00:20:36.000
but that would make the call of it a little bit longer,

00:20:36.000 --> 00:20:39.120
I think this is a nice middle ground. But of course, you do with your code

00:20:39.120 --> 00:20:42.000
whatever you think is best. Now, we have the code to get

00:20:42.000 --> 00:20:44.240
the import path, we can copy this line

00:20:46.120 --> 00:20:47.720
into our Reload operator.

00:20:49.120 --> 00:20:51.120
And then we can get this line,

00:20:53.240 --> 00:20:57.480
and put that here. And now, all we have to do is get from the Import Path,

00:20:57.480 --> 00:21:00.480
which is a directory, to the Import File Path,

00:21:00.480 --> 00:21:05.120
which is a file name. And the Import File Path is the

00:21:05.120 --> 00:21:11.960
"import_ path / mass_import_fname" that we took a copy of up there.

00:21:13.600 --> 00:21:16.480
Path Object in Python supports this "/" notation.

00:21:16.480 --> 00:21:19.000
It wil work correctly automatically for any platform.

00:21:19.000 --> 00:21:23.000
On Windows, it uses the back slash, on Linux and Mac OS, it uses the "/".

00:21:23.000 --> 00:21:26.000
Now that we have constructed the file name,

00:21:26.000 --> 00:21:28.840
can pass it to the operator that loads the OBJ files.

00:21:28.840 --> 00:21:31.360
Now, all that's left is to restore whatever we wanted to restore.

00:21:31.360 --> 00:21:34.840
So again, we have to loop over the selected object,

00:21:34.840 --> 00:21:36.840
and set the Mass Import file name.

00:21:44.480 --> 00:21:46.080
Now, we have to restore the Matrix.

00:21:50.240 --> 00:21:52.360
Will tell Blender that the operator did its job.

00:21:55.480 --> 00:22:00.480
And then we fix two typos. Here ":", and here, has to use "collection",

00:22:00.480 --> 00:22:02.480
not "collections".

00:22:03.600 --> 00:22:06.480
Finally, what we have to do is Register and Unregister the operator

00:22:06.480 --> 00:22:08.600
and add a button to the panel.

00:22:10.840 --> 00:22:13.720
We copied the class name, we added to this list,

00:22:16.480 --> 00:22:20.000
We copy the BL ID name and added to the panel,

00:22:23.840 --> 00:22:24.720
save the file,

00:22:25.840 --> 00:22:28.120
reload the script, and there, we have our button.

00:22:30.360 --> 00:22:34.120
As you can see, we click on it. And as you use from importing OBJ files,

00:22:34.120 --> 00:22:37.360
there is no active object anymore,

00:22:37.360 --> 00:22:41.600
just imported objects are selected, in this case, Suzanne.

00:22:41.600 --> 00:22:42.960
Now, let's see if it really reloads.

00:22:44.120 --> 00:22:48.240
I put a new file in there "cube.obj", and now it should replace Suzanne

00:22:48.240 --> 00:22:52.360
with that Cube. And it does, so there we have it.

00:22:52.360 --> 00:22:56.480
Our code is working, we can mass load OBJ files,

00:22:56.480 --> 00:22:59.600
and we can select individual objects to reload. I will leave it as an exercise

00:22:59.600 --> 00:23:02.840
for you to make a mass reload operator

00:23:02.840 --> 00:23:06.080
that iterates over all the objects, or maybe only all the selected objects.

00:23:06.080 --> 00:23:09.240
I'll leave that up to you. So this is it for this episode

00:23:09.240 --> 00:23:12.000
of Scripting for Artists. This is not the last time

00:23:12.000 --> 00:23:14.480
we'll talk about Custom Properties,

00:23:14.480 --> 00:23:17.120
but I think this video has gone on long enough already. If you have any questions

00:23:17.120 --> 00:23:19.720
but I think this video or comments, leave them below,

00:23:19.720 --> 00:23:20.120
and I will see you soon.