WEBVTT 00:00:00.120 --> 00:00:02.360 Hello and welcome to Scripting for Artists. My name is Sybren. 00:00:02.360 --> 00:00:05.080 And in this episode, I will show you how to create 00:00:05.080 --> 00:00:06.080 your own operator. 00:00:07.000 --> 00:00:09.960 So far, we only created snippets of code, you can use them, 00:00:09.960 --> 00:00:12.720 but they're not the most user friendly. 00:00:12.720 --> 00:00:16.600 Many people have asked ways to create menus and buttons and custom panels and stuff. 00:00:16.600 --> 00:00:20.240 In this episode, we will not look at that yet. 00:00:20.240 --> 00:00:22.840 But we will look at a necessary first Step, which is, 00:00:22.840 --> 00:00:23.960 creating your first operator. 00:00:26.240 --> 00:00:29.120 We will look at what an operator is exactly, then, 00:00:29.120 --> 00:00:31.720 we will see how to create your own operator and how to make it 00:00:31.720 --> 00:00:34.960 more flexible by passing parameters to it. And then, 00:00:34.960 --> 00:00:38.720 we conclude by limiting the operator to specific context. 00:00:38.720 --> 00:00:42.080 An operator is the glue between menus, buttons, and hotkeys, 00:00:42.080 --> 00:00:44.480 and the code that should be executed by them. In the first episode, 00:00:44.480 --> 00:00:47.480 we already worked with operators by copy pasting them 00:00:47.480 --> 00:00:51.600 from menus and buttons into our own script. Operators can be implemented 00:00:51.600 --> 00:00:54.840 in Blender itself in the C programming language. 00:00:54.840 --> 00:00:57.960 Or, they can, of course, be written in Python. 00:00:57.960 --> 00:01:01.720 No matter how they're made, they all have the same ingredients. 00:01:01.720 --> 00:01:05.000 First is an identifier. So this is what you would put after the "bpy.ops", 00:01:05.000 --> 00:01:09.600 so in this Operator, for example, it's far from complete, 00:01:09.600 --> 00:01:13.480 but we're building it up. So in this example, it would be 00:01:13.480 --> 00:01:17.840 "bpy.ops.sfa.example". These are always in the form 00:01:17.840 --> 00:01:21.600 "some category.a name". Best pick a category 00:01:21.600 --> 00:01:25.480 that already exist, like object or mesh or sculpt 00:01:25.480 --> 00:01:29.080 or whatever is suitable for your operator. But as you can see, 00:01:29.080 --> 00:01:32.000 you can also create your own. Then, we have a label. 00:01:32.000 --> 00:01:35.080 This is what appears on the menu items and buttons, 00:01:35.080 --> 00:01:39.360 and a description that is shown as Tool Tip. Then, everything is combined 00:01:39.360 --> 00:01:42.480 into a class. And this is something that we'll look at in a minute. 00:01:42.480 --> 00:01:46.360 For now, just think of it as some pot in which 00:01:46.360 --> 00:01:49.840 we gather all the ingredients of our operator. You can see that 00:01:49.840 --> 00:01:52.080 the class is named after the operator. So we have the category 00:01:52.080 --> 00:01:55.960 in capitals, then OT for the operator type, and then 00:01:55.960 --> 00:01:59.960 the rest of the identifier. So far, we've seen description, 00:01:59.960 --> 00:02:02.720 but not actual code yet. And this can be added in different ways 00:02:02.720 --> 00:02:05.960 for different purposes. So here are the possibilities 00:02:05.960 --> 00:02:09.840 from simple to complex. You have "Execute", this is where you put 00:02:09.840 --> 00:02:13.360 the main functionality of the code. If you want to create 600 monkeys, 00:02:13.360 --> 00:02:17.000 then this is the place to do it. The Execute function is also 00:02:17.000 --> 00:02:20.000 what gets called from Python directly. So if you call an operator, 00:02:20.000 --> 00:02:23.240 like "bpy.something.something" 00:02:23.240 --> 00:02:26.480 that's the function that gets called. Then we have "Invoke", 00:02:26.480 --> 00:02:29.240 this function is called when the operator is called for a menu 00:02:29.240 --> 00:02:32.600 or a button. If you want to do something extra, in that case, 00:02:32.600 --> 00:02:34.960 you want to have slightly different behavior, then you 00:02:34.960 --> 00:02:38.240 can do that in Invoke and you then call your Execute function from there. 00:02:38.240 --> 00:02:43.120 And now, we get to the most complex, the Modal one. 00:02:43.120 --> 00:02:45.840 The Modal function is for special operators that need to run 00:02:45.840 --> 00:02:48.720 for a longer period of time. This receives all kinds of events 00:02:48.720 --> 00:02:51.360 from Blender, from when you move your mouse, 00:02:51.360 --> 00:02:54.840 you click on buttons, you use the keyboard, that kind of stuff. 00:02:54.840 --> 00:02:57.840 Things like the Blender Cloud, texture browser, or CG cougars, 00:02:57.840 --> 00:03:01.000 Retopo, Float, Implemented, like this. If after all of these, 00:03:01.000 --> 00:03:03.720 you are in doubt about which function to use, keep it simple, 00:03:03.720 --> 00:03:07.120 just use the Execute function. If that turns out not to to be able to do 00:03:07.120 --> 00:03:09.960 what you want to do, then you have a concrete reason 00:03:09.960 --> 00:03:13.120 to look at something more complex. But before that, 00:03:13.120 --> 00:03:14.000 just keep things simple. 00:03:15.000 --> 00:03:17.360 Now, let's turn this into an actual operator that we can use. 00:03:17.360 --> 00:03:19.240 Let's create some more monkeys. 00:03:20.480 --> 00:03:23.600 Let's start by removing what we don't need. Let's keep it simple, 00:03:23.600 --> 00:03:30.360 just an Execute function. If you look at the Mesh Operators, 00:03:30.360 --> 00:03:33.360 you can see that, they start with "bpy.ops mesh primitive monkey add", 00:03:33.360 --> 00:03:38.080 or "bpy.ops mesh primitive ico sphere add" 00:03:38.080 --> 00:03:40.600 So all the Operators that create a new mesh object, 00:03:40.600 --> 00:03:44.360 they start with "mesh". So let's keep doing that. 00:03:45.840 --> 00:03:49.120 So the ID name becomes "mesh" and we're going to create a monkey grid. 00:03:52.080 --> 00:03:58.240 Monkey Grid, label "monkey grid", the Tool Tip will be 00:03:58.240 --> 00:04:00.960 "let's spread some joy" 00:04:02.240 --> 00:04:05.360 and then the class name, we have to change, that becomes the category 00:04:05.360 --> 00:04:08.240 "mesh_ot_monkey_grid". 00:04:09.960 --> 00:04:14.080 The Execute function has to do something, 00:04:14.080 --> 00:04:17.720 but it also has to tell Blender whether everything succeeded or not. 00:04:17.720 --> 00:04:23.120 So everything was alright, you return "finished" 00:04:23.120 --> 00:04:26.600 and that tells Blender that the code actually performed well, 00:04:26.600 --> 00:04:30.000 but maybe your Operator cannot work, maybe it is for extruding a mesh 00:04:30.000 --> 00:04:32.720 and the mesh doesn't have any vertices. 00:04:33.720 --> 00:04:37.480 So in that case, you return "cancelled". There are a few other options 00:04:37.480 --> 00:04:41.600 and they are all described in the menu. To go there, 00:04:41.600 --> 00:04:45.240 you go to Help and then Python API Reference, and then 00:04:45.240 --> 00:04:49.120 to the section about "bpy.ops". So let's assume that 00:04:49.120 --> 00:04:50.600 everything will work correctly, 00:04:52.240 --> 00:04:56.080 we will return "finished". And now, all we have to do is 00:04:56.080 --> 00:04:58.240 put the code here that creates our monkey grid. 00:04:59.240 --> 00:05:01.720 So let's copy the code from Chapter 3 of Scripting for Artists 00:05:01.720 --> 00:05:07.120 and put it here. So this creates our 600 monkeys in rows of 25, 00:05:07.120 --> 00:05:12.840 having one Blender Unit between them. 00:05:12.840 --> 00:05:16.120 The Operators almost done already. So we have all the ingredients here. 00:05:16.120 --> 00:05:19.120 The only thing that we need to do now is 00:05:19.120 --> 00:05:22.600 tell Blender that this operator exists and this is called Registration. 00:05:24.840 --> 00:05:27.600 Fortunately, this is ather simple, we just call 00:05:27.600 --> 00:05:30.960 "bpy.utils.register_class" and then the name of the class, 00:05:30.960 --> 00:05:35.960 in our case, "mesh OT monkey grid". For symmetry, there should also be 00:05:35.960 --> 00:05:39.960 a Unregister function. So that looks like this. 00:05:39.960 --> 00:05:43.240 Instead of calling "register class", it's called "unregister class". 00:05:43.240 --> 00:05:46.840 Basically it undoes what the register function was doing, and then, 00:05:46.840 --> 00:05:50.720 we're almost there. It's just that, as you know, when you have 00:05:50.720 --> 00:05:53.480 a function like this, it's not automatically called when you run the script. 00:05:53.480 --> 00:05:57.720 There's a little trick for this. 00:05:57.720 --> 00:06:01.600 If you add some magic like this in here, and it looks a bit weird. 00:06:01.600 --> 00:06:06.000 But basically what this means is that, if this script is run, 00:06:06.000 --> 00:06:09.480 then it should call the Register function. 00:06:09.480 --> 00:06:13.120 There's multiple ways in which Blender can access your script, 00:06:13.120 --> 00:06:17.480 it can execute it, but it can also be imported from something else, 00:06:17.480 --> 00:06:21.720 just like we import BPY, other code can import this file as well. 00:06:21.720 --> 00:06:25.080 So there's a distinction between being imported from somewhere else, 00:06:25.080 --> 00:06:28.840 and being run. And only when it's being run, 00:06:28.840 --> 00:06:31.720 should it called the Register function, and that is what this code does. 00:06:31.720 --> 00:06:37.000 So now, what we can do, let's just name this "monkey_grid.py", 00:06:40.120 --> 00:06:41.480 and then let's click play. 00:06:43.120 --> 00:06:47.600 And nothing happened, which is kind of a good thing. 00:06:47.600 --> 00:06:51.600 We didn't see any error message, our code doesn't show any message. 00:06:51.600 --> 00:06:53.080 So silence is kind of good here. 00:06:54.120 --> 00:06:59.000 So, let's see what happens now, 00:07:00.600 --> 00:07:01.120 "bpy.ops.mesh.monkey_grid", 00:07:03.600 --> 00:07:06.600 there we go, we can create a monkey grid. 00:07:06.600 --> 00:07:09.600 The operator is there. Let's spread some joy. Let's not call it here. 00:07:09.720 --> 00:07:13.600 Let's see if we can find our new operator here in the F3 menu 00:07:15.000 --> 00:07:17.960 with a monkey and there's your monkey grid. So that's really cool. 00:07:17.960 --> 00:07:21.720 Press "enter" to execute it. And as you can see, 00:07:21.720 --> 00:07:24.960 Blender now freezes one is creating the 600 monkeys. 00:07:24.960 --> 00:07:27.240 And this is what happens when you do something that takes time 00:07:27.360 --> 00:07:31.120 in the Execute function, and that is okay. The code is part of 00:07:31.120 --> 00:07:34.840 this Blend file. So, let's see what happens when we create a new Blend file. 00:07:38.240 --> 00:07:40.120 As you can see, the operator is still there. 00:07:40.120 --> 00:07:43.120 Has been loaded into memory of Blender. It's been registered 00:07:43.120 --> 00:07:46.480 and it just keeps taking around. Now, let's see what happens 00:07:46.480 --> 00:07:47.600 if we restart Blender. 00:07:52.120 --> 00:07:55.080 And now, the monkey grid operator is no longer there. 00:07:55.080 --> 00:07:58.000 This is because, Blender doesn't just execute all the scripts 00:07:58.000 --> 00:08:00.960 that it can find in a Blend file, you have to tell it to do that first. 00:08:00.960 --> 00:08:04.120 You have to make sure that the name of the text file 00:08:04.120 --> 00:08:08.480 ends in ".py", and then here in the Text menu, 00:08:08.480 --> 00:08:10.000 you can check the Registered checkbox. 00:08:11.000 --> 00:08:13.120 Now, let's save, restart Blender, 00:08:16.720 --> 00:08:20.080 and now it's there. So let's have some fun and add some parameters. 00:08:20.080 --> 00:08:23.960 When you add a cube, what you see here on the left 00:08:23.960 --> 00:08:27.360 is called the Redo panel. When you open it, you see different parameters 00:08:27.360 --> 00:08:30.000 which you can set. So what happens is that, 00:08:30.000 --> 00:08:33.360 when you change the parameters value, Blender pushes the Undo button 00:08:33.360 --> 00:08:37.360 automatically, and then re-execute the operator. 00:08:37.360 --> 00:08:39.840 That is why it's called the Redo panel, because it redoing things 00:08:39.840 --> 00:08:43.000 all the time. So let's add support for the Redo panel to our operator. 00:08:43.000 --> 00:08:46.360 We start by declaring the properties we want to have. 00:08:46.360 --> 00:08:49.600 This will be the number of monkeys in the X direction, 00:08:49.600 --> 00:08:52.600 number of monkeys in the Y direction, and monkey size. 00:08:52.600 --> 00:08:55.960 Just like operators live in "bpy.ops", 00:08:55.960 --> 00:09:00.000 the properties live in "bpy.props". So again, if you want 00:09:00.000 --> 00:09:03.120 to have more information, just go to Help, Python, API Reference, 00:09:03.120 --> 00:09:06.840 and then click on the "bpy.props" section. I will show you 00:09:06.840 --> 00:09:12.080 what it looks like. Let's call it "count x: bpy.props.IntProperty". 00:09:17.720 --> 00:09:20.960 IN stands for integer, which means a whole number, 00:09:20.960 --> 00:09:25.000 because we cannot have half monkey. So count X has to be either one or two or three, 00:09:25.000 --> 00:09:29.240 but can never be like 2.5 or something. So it's whole numbers only, 00:09:29.240 --> 00:09:33.960 and this declares that we want to have that property. 00:09:33.960 --> 00:09:36.840 There is a big difference between the ":" we have here, 00:09:36.840 --> 00:09:40.240 and the "=" sign we have there. 00:09:41.360 --> 00:09:44.960 This sets a name to a value, and this is for things 00:09:44.960 --> 00:09:48.000 that just have to be set. We have to set "BL ID name" to match 00:09:48.000 --> 00:09:52.080 "monkey grid" to make it work. But here we don't really set anything. 00:09:52.080 --> 00:09:55.840 We just declare to Blender, this is an IN property, 00:09:55.840 --> 00:09:59.080 please act accordingly. 00:09:59.080 --> 00:10:02.480 You can add some parameters here to change behavior. 00:10:02.480 --> 00:10:03.360 First of all, we should set a name. 00:10:04.600 --> 00:10:07.120 We can call it X. It may be a bit cryptic, 00:10:07.120 --> 00:10:07.600 but for now, will do. 00:10:08.960 --> 00:10:10.480 And we can add a description, 00:10:11.480 --> 00:10:17.000 "number of monkeys in the X direction". 00:10:18.480 --> 00:10:20.080 So let's copy this to the Y. 00:10:22.080 --> 00:10:27.360 name this Y and "number of monkeys in the Y direction", and whatever size, 00:10:27.360 --> 00:10:30.720 which is another "bpy.props.FloatProperty". 00:10:32.480 --> 00:10:36.120 Float stands for floating point, 00:10:36.120 --> 00:10:38.720 is a technical term for just decimal numbers. 00:10:40.360 --> 00:10:48.120 "Name = size", and "Description = size of each monkey", 00:10:48.120 --> 00:10:51.600 this gives us our properties, but they're not used yet. So let's take a look 00:10:51.600 --> 00:10:54.720 at the Execute function where we're supposed to use them. 00:10:54.720 --> 00:10:59.000 This comment, it has to go, because we no longer creating 600 monkeys 00:10:59.000 --> 00:11:04.240 in rows of 25, but it's all flexible, so let's remove that for now. 00:11:04.240 --> 00:11:08.080 Now we have to access the properties. So we've declared them 00:11:08.080 --> 00:11:12.360 and this "self" gives us access to the actual value. 00:11:12.360 --> 00:11:15.960 "Self" is a point thing and I won't go into detail here 00:11:15.960 --> 00:11:20.080 about what it represents. Just know that, if you declare 00:11:20.080 --> 00:11:23.840 a property here as count X, then you can access it here as "self.count X". 00:11:25.960 --> 00:11:27.480 So the total number of monkeys 00:11:28.840 --> 00:11:32.840 is the number of monkeys in the X and in the Y direction, 00:11:32.840 --> 00:11:36.480 and this 25 here was the number of monkeys in the X direction. 00:11:41.480 --> 00:11:43.960 And then, all that is left is to set a size, and that's it. 00:11:45.000 --> 00:11:47.120 Let's give it a try. 00:11:49.840 --> 00:11:51.480 Let's see what happens in the Console. 00:11:55.720 --> 00:11:58.360 There you can see our Properties, count X, count Y, size, 00:11:58.360 --> 00:12:02.080 and they're all equal to 0, because we haven't set any default yet. 00:12:09.360 --> 00:12:13.240 And there, we have our three monkeys. 00:12:13.240 --> 00:12:16.600 Before we actually call it from the Viewport, 00:12:16.600 --> 00:12:17.840 let's set some sensible defaults. 00:12:20.960 --> 00:12:22.080 Default is 3. 00:12:23.840 --> 00:12:27.080 For the Y, default is 2, I choose different values there on purpose. 00:12:27.080 --> 00:12:30.960 This is default, so when somebody clicks on monkey grid button, 00:12:30.960 --> 00:12:33.960 or select it from the F3 list", 00:12:33.960 --> 00:12:38.120 this will be what they see. Because they see a 3x2 grid, 00:12:38.120 --> 00:12:41.080 they immediately know what they need to change. 00:12:41.080 --> 00:12:43.840 If they want to change the 3 to a 4, that just change the 3 to a 4, 00:12:43.840 --> 00:12:46.960 without having to think about whether it's the X or the Y direction. 00:12:46.960 --> 00:12:50.840 So if we were to give them the same default, 00:12:50.840 --> 00:12:52.960 then they wouldn't be able to see it. And then, they would have the thing 00:12:52.960 --> 00:12:56.000 like which direction is X, which direction is Y, 00:12:56.000 --> 00:12:59.240 which value do I want to change. And this is why I give them distinct values. 00:13:04.600 --> 00:13:07.720 Finally, default for the size, run again, 00:13:10.000 --> 00:13:11.360 delete everything. 00:13:16.120 --> 00:13:18.480 And there, you can see your defaults. And when we execute 00:13:18.480 --> 00:13:21.480 without any values, it just uses those default. 00:13:24.080 --> 00:13:27.120 And the same for the F3 menu. There's one more step left, 00:13:27.120 --> 00:13:30.360 and that is, to get that Redo panel. We have the properties, 00:13:30.360 --> 00:13:33.720 so Blender knows what should hypothetically go in there, 00:13:33.720 --> 00:13:37.600 it just doesn't know yet that we support that Redo panel. 00:13:37.600 --> 00:13:40.960 So let's tell Blender that we do. 00:13:43.480 --> 00:13:46.720 This is done through "bl options". The default value is "register", 00:13:47.960 --> 00:13:53.840 and we have to add "undo" to it. This will give us the final ingredient. 00:13:53.840 --> 00:13:57.600 There you go. 00:13:58.960 --> 00:14:02.240 Now we can make them big and small, and give them even invalid values. 00:14:02.240 --> 00:14:06.080 So to make it pleasant to use for people, 00:14:06.080 --> 00:14:09.720 we should really set limits to the slider, so that, 00:14:09.720 --> 00:14:12.840 it's all sensible values that you can select there. 00:14:12.840 --> 00:14:14.120 Fortunately, this is quite simple. 00:14:15.240 --> 00:14:18.720 We can set a minimum. Let's set it to 1 because creating 0 monkey 00:14:18.720 --> 00:14:22.480 doesn't make sense. And creating negative monkeys even less. 00:14:22.480 --> 00:14:27.600 So let's start at 1, let's set the maximum to 10 for now. 00:14:30.480 --> 00:14:32.120 We can do the same for the count Y, 00:14:33.120 --> 00:14:37.600 and we can set the size 0 to minimum, and the maximum, 00:14:37.600 --> 00:14:39.080 let's set it to 1. 00:14:45.080 --> 00:14:48.600 And now, we can drag and things are still nice and sane. 00:14:51.360 --> 00:14:53.600 You can see that, it already gets little bit slower 00:14:53.600 --> 00:14:58.000 when these numbers increase. And we still can't get to the 600 we had before, 00:14:58.000 --> 00:15:01.840 even when I type 100 here, it is cut off to the maximum. 00:15:01.840 --> 00:15:05.600 So this is why Blender has a soft limit. 00:15:05.600 --> 00:15:09.240 The hard limit is what we set now, that's the absolute limit 00:15:09.240 --> 00:15:12.120 of the value of the property. Whereas the soft limit is 00:15:12.120 --> 00:15:14.240 what the slider will do when you drag around. 00:15:15.240 --> 00:15:18.960 So if you want to allow maximum values that are bigger than 10, 00:15:18.960 --> 00:15:22.720 or sizes that are bigger than 1, but still want these limits 00:15:22.720 --> 00:15:26.240 as the limit for the slider, you can change the maximum into a soft maximum. 00:15:26.240 --> 00:15:30.080 The minimum that we have now really is a minimum, 00:15:30.080 --> 00:15:32.480 because creating 0 monkeys doesn't make sense, 00:15:32.480 --> 00:15:35.480 negative monkeys is impossible, also, creating a negatively sized monkey 00:15:35.480 --> 00:15:39.080 is impossible. So let's change the maximum to soft. 00:15:44.840 --> 00:15:53.120 Now the dragging is still the same, but we can set it to create 00:15:53.120 --> 00:15:56.720 much more monkeys than you would get with dragging. 00:15:56.720 --> 00:16:00.120 Now, let's get back to that class declaration. 00:16:00.120 --> 00:16:03.080 I'll explain a little bit more about how classes work in an inituitive way, 00:16:03.080 --> 00:16:06.720 I hope, without going too much into technical details. 00:16:06.720 --> 00:16:10.360 Classes use a system called inheritance, 00:16:10.360 --> 00:16:15.080 just like with people, it's like a parent-child structure. 00:16:15.080 --> 00:16:20.480 So in this case, "bpy.types.operator" is the parent, and "mesh OT monkey grid" 00:16:20.480 --> 00:16:24.120 access to the child. If you ask a child a question that 00:16:24.120 --> 00:16:27.720 you know the answer to, say you want to have a cookie, 00:16:27.720 --> 00:16:30.360 the child will say yes immediately without asking the parent, of course. 00:16:30.360 --> 00:16:35.000 But if you ask about taxes, then "Mom, please help me out here, 00:16:35.000 --> 00:16:38.240 because I don't know anything!" and then the child defers 00:16:38.240 --> 00:16:43.080 that question to the parent. This is the same way 00:16:43.080 --> 00:16:46.080 that Classes work in Python, roughly. 00:16:47.080 --> 00:16:50.000 We could do without the "bl" options. Our child didn't know 00:16:50.000 --> 00:16:53.600 anything about it, so Python asked the parent. 00:16:54.720 --> 00:16:57.480 And when we want to have something different, 00:16:57.480 --> 00:17:02.480 we can add "bl" options to our child, to our class. And then, that is asked first, 00:17:02.480 --> 00:17:05.480 so that takes precedence over whatever the parents wants. 00:17:05.480 --> 00:17:08.840 So we always have lucky children who gets all the cookies they want. 00:17:11.600 --> 00:17:14.000 So before I end this video, I have two more things 00:17:14.000 --> 00:17:18.240 I want to tell you. One, again, we look at the Execute function. 00:17:18.240 --> 00:17:21.480 You see that it gets a Context Parameter and this is pretty much like 00:17:21.480 --> 00:17:25.240 the context we've seen before. It gives us "context. object", 00:17:25.240 --> 00:17:28.960 "context.scene", "context.selected object", 00:17:28.960 --> 00:17:32.000 all these things you've seen before in "bpy.context", 00:17:32.000 --> 00:17:36.240 it gets here as well, but then, localized specifically for this operator. 00:17:36.240 --> 00:17:39.720 So as a general rule of thumb, 00:17:39.720 --> 00:17:43.480 if you have a function that gets a Context, use that Context, 00:17:43.480 --> 00:17:46.840 don't use "bpy.context. So if you want to do something 00:17:46.840 --> 00:17:50.960 with all the selected pose bones in this Execute function, 00:17:50.960 --> 00:17:53.080 you would use "context.selected pose bone". 00:17:57.720 --> 00:17:59.840 Another function and that is the second thing that I wanted to show you, 00:17:59.840 --> 00:18:03.240 another function that gets a Context is the Poll function, 00:18:03.240 --> 00:18:08.240 and it's written in a bit weird way, but just take it from me, 00:18:08.240 --> 00:18:09.720 it works like that. 00:18:18.080 --> 00:18:21.360 Again, you get a Context in this function. But instead of 00:18:21.360 --> 00:18:25.600 doing something like, instead of performing an action, 00:18:25.600 --> 00:18:28.240 this function is meant to check whether that action will be possible. 00:18:28.240 --> 00:18:32.360 So this Poll function is called by Blender 00:18:32.360 --> 00:18:35.960 every time this Operator is supposed to show up in a menu, 00:18:35.960 --> 00:18:39.960 or as a button on a panel. I can show you how this works. 00:18:39.960 --> 00:18:43.840 Right now, returns "true", which means that it is always allowed, 00:18:43.840 --> 00:18:47.960 just as it was before. And just as it was before, 00:18:47.960 --> 00:18:49.240 it shows up here in the F3 menu. 00:18:50.240 --> 00:18:51.720 When I change it to "false", 00:18:53.240 --> 00:18:57.120 it will never show up anywhere, which is kind of useless. 00:18:57.120 --> 00:18:59.720 Let's tweak this to make it a bit more useful. 00:19:00.720 --> 00:19:02.360 You can see here, in the Console, 00:19:04.480 --> 00:19:07.120 we have Autocomplete, which makes sense in a Python Console. 00:19:07.120 --> 00:19:10.960 But that same operator does not work 00:19:11.960 --> 00:19:16.080 in the 3D Viewport, because the context is wrong. This is also something 00:19:16.080 --> 00:19:19.360 we can do ourselves. Right now, when I change this to "true" again, 00:19:23.240 --> 00:19:26.600 the monkey grid operator also shows up in the context of the Python comes on. 00:19:26.600 --> 00:19:29.720 And it will show up anywhere in Blender, 00:19:29.720 --> 00:19:33.240 which is not exactly the right way to go. Let's take another look 00:19:33.240 --> 00:19:35.960 at a variable inside that context. 00:19:37.240 --> 00:19:41.120 "Context.area" gives you the area that is currently active 00:19:41.120 --> 00:19:44.240 in Blender User Interface. So in this case, it would be the Console. 00:19:44.240 --> 00:19:47.960 But if the mouse is here, and we pull up the 3 menus, 00:19:47.960 --> 00:19:51.240 then all of a sudden, its 3D Viewport that is active, and here, 00:19:51.240 --> 00:19:55.120 would be the Outliner. So every area in Blender has its own area type 00:19:55.120 --> 00:19:59.080 and we can use that in our Poll function to make sure that 00:19:59.080 --> 00:20:02.120 it's only working in the area 00:20:02.120 --> 00:20:05.720 where we wanted to work. One thing I don't really like is guesswork. 00:20:05.720 --> 00:20:09.720 So we know now that the Area Type of the console is Console, 00:20:09.720 --> 00:20:14.960 but is it in 3D Viewport? Is it "3D View"? "3D_view", is it "3D Viewport"? 00:20:14.960 --> 00:20:19.840 I don't know, so let's make our script tell us instead. 00:20:19.840 --> 00:20:27.720 I can just say "print my area is context.area.type" 00:20:30.240 --> 00:20:33.720 And let's see what happens on the terminal where all these prints 00:20:33.720 --> 00:20:35.080 are sent to. 00:20:36.240 --> 00:20:40.120 Here, you seen the console, and immediately, you see it being called 00:20:40.120 --> 00:20:43.720 "My area is view 3D". But when I do it here in the Outliner, 00:20:43.720 --> 00:20:47.360 my area is Outliner. If I do it here in the Properties panel, 00:20:47.360 --> 00:20:52.000 my area is Properties. So that way, you can just use these print statements 00:20:52.000 --> 00:20:56.360 to know what you have to put where. 00:20:56.360 --> 00:20:59.600 So now, we know which value to use for the 3D Viewport, 00:20:59.600 --> 00:20:59.960 so let's just do that. 00:21:00.960 --> 00:21:07.600 If "context.area.type=view 3D" then return "true", 00:21:07.600 --> 00:21:11.960 otherwise, we can return "false". Let's see how this works. 00:21:15.480 --> 00:21:16.960 Here, it still shows up. 00:21:18.360 --> 00:21:23.000 But here is no longer there and, of course, here and there, 00:21:23.000 --> 00:21:27.120 now it only shows up where we want it to show up. One final thing, 00:21:28.240 --> 00:21:31.600 this kind of construct, I see them a lot, also from experienced programmers, 00:21:31.600 --> 00:21:34.480 it's more complex than necessary. 00:21:34.480 --> 00:21:39.240 Because this guy is already an expression that is true or false. 00:21:39.240 --> 00:21:43.240 So basically, what the code is saying is that 00:21:43.240 --> 00:21:48.480 if the value of this thing, this selected expression, 00:21:48.480 --> 00:21:52.240 if the value of that thing is true, return true, and if the value 00:21:52.240 --> 00:21:56.720 of that thing is false, return false. So that basically means 00:21:56.720 --> 00:22:00.480 return the value of this thing, which you can of course write 00:22:00.480 --> 00:22:00.960 as this. 00:22:05.840 --> 00:22:08.600 So that was it for this episode of Scripting for Artists. 00:22:08.600 --> 00:22:10.960 If you have any questions or remarks, please leave a comment below, 00:22:10.960 --> 00:22:12.840 and I will see you soon.