GPv3: Python API: GreasePencilFrame #116045

New Issue

Falk David · 2023-12-11T16:43:35+01:00

Falk David commented

2023-12-11 16:43:35 +01:00

We need a Python API for the GreasePencilFrame. See GreasePencilFrame in DNA_grease_pencil_types.h and class Layer in BKE_grease_pencil.hh

The layer needs a collection property:

Add a new collection property frames in rna_def_grease_pencil_layer.
This will need a custom collection iterator that iterates over the layer.frames(). Use the sorted_keys() cache so that the collection returns the elements sorted by the scene time.

The GreasePencilFrame should have

a pointer drawing to a GreasePencilDrawing (which can just be a stub for now).
a property for the keyframe time
a property with the selection status

We need a Python API for the `GreasePencilFrame`. See `GreasePencilFrame` in `DNA_grease_pencil_types.h` and `class Layer` in `BKE_grease_pencil.hh` The layer needs a collection property: * Add a new collection property `frames` in `rna_def_grease_pencil_layer`. * This will need a custom collection iterator that iterates over the `layer.frames()`. Use the `sorted_keys()` cache so that the collection returns the elements sorted by the scene time. The `GreasePencilFrame` should have * a pointer `drawing` to a `GreasePencilDrawing` (which can just be a stub for now). * a property for the keyframe time * a property with the selection status

Falk David added the

Type

To Do

label 2023-12-11 16:43:35 +01:00

Falk David added this to the Grease Pencil project 2023-12-11 16:43:43 +01:00

Falk David referenced this issue

2023-12-11 16:44:37 +01:00

GPv3: Python API #116043

Falk David referenced this issue

2023-12-11 16:45:11 +01:00

Documentation: Changes between Grease Pencil v2 and Grease Pencil v3 #114419

Jaime Torres commented

2023-12-12 01:03:58 +01:00

Given what we talked, could i take care of this as a first step?

Falk David commented

2023-12-12 08:56:41 +01:00

@mewslore Yes :)

❤️ 1 🎉 1

Jaime Torres commented

2023-12-15 20:55:54 +01:00

Alright, I'm forking the repository and I'll work from there. Is there anything else i should take into account?

Falk David commented

2023-12-16 09:05:01 +01:00

@mews6 If you haven't already, then this is good to read https://wiki.blender.org/wiki/Tools/Pull_Requests

Jaime Torres commented

2024-01-07 09:23:27 +01:00

Alright, it's been a while, and i took a break to celebrate the holidays with my family (which is why i've been so silent as of late, sorry for that). However, i already took a look into the documentation of the existing Python API and i've been reading the files you suggested. And there's a few questions i have before coding anything:

Where would we locate the class? classes inside of files with other information is a thing that happens in Blender's souce code, so i'm not sure if there is already a place where this class should be. Would it share a file with other classes?
When you mention "a pointer drawing to a GreasePencilDrawing" are we talking about an actual pointer from C/C++?
Given the fact that we're making a pointer towards an instance of GreasePencilDrawing, could this code be merged without that class existing? If not, then could drawing be a null? (which i'd imagine could be the case if this code can be merged without it)

I'll probably keep asking either here or in the chat when i run into trouble. But for now, those are my main questions.

Alright, it's been a while, and i took a break to celebrate the holidays with my family (which is why i've been so silent as of late, sorry for that). However, i already [took a look into the documentation of the existing Python API](https://docs.blender.org/api/current/index.html) and i've been reading the files you suggested. And there's a few questions i have before coding anything: - Where would we locate the class? classes inside of files with other information is a thing that happens in Blender's souce code, so i'm not sure if there is already a place where this class should be. Would it share a file with other classes? - When you mention "a pointer `drawing` to a `GreasePencilDrawing`" are we talking about an actual pointer from C/C++? - Given the fact that we're making a pointer towards an instance of `GreasePencilDrawing`, could this code be merged without that class existing? If not, then could `drawing` be a null? (which i'd imagine could be the case if this code can be merged without it) I'll probably keep asking either here or in the chat when i run into trouble. But for now, those are my main questions.

Falk David commented

2024-01-08 11:15:45 +01:00

@mews6 Welcome back :) (no need to apologize!)

If you mean the Layer class then the location is blender/source/blender/blenkernel/BKE_grease_pencil.hh:333 (here).
Good question. I should have clarified a bit. I'm talking about an RNA pointer. See here for an existing example. The string that is used in RNA_def_property_struct_type is the name of the RNA struct defined with RNA_def_struct_sdna (here).
There is a C++ struct GreasePencilDrawing in blender/source/blender/makesdna/DNA_grease_pencil_types.h (here). But what I mean with "this can be a stub for now" is that you just define GreasePencilDrawing using RNA_def_struct_sdna (see how it's done for the RNA for layers) but not add any props etc. to it. It can just be an empty container for now.

@mews6 Welcome back :) (no need to apologize!) * If you mean the `Layer` class then the location is `blender/source/blender/blenkernel/BKE_grease_pencil.hh:333` ([here](https://projects.blender.org/blender/blender/src/commit/4dad262dbe892e169b0caa8f6d6c6ae41a46eb02/source/blender/blenkernel/BKE_grease_pencil.hh#L333)). * Good question. I should have clarified a bit. I'm talking about an RNA pointer. See [here](https://projects.blender.org/blender/blender/src/commit/4dad262dbe892e169b0caa8f6d6c6ae41a46eb02/source/blender/makesrna/intern/rna_grease_pencil.cc#L238) for an existing example. The string that is used in `RNA_def_property_struct_type` is the name of the RNA struct defined with `RNA_def_struct_sdna` ([here](https://projects.blender.org/blender/blender/src/commit/4dad262dbe892e169b0caa8f6d6c6ae41a46eb02/source/blender/makesrna/intern/rna_grease_pencil.cc#L182)). * There is a C++ struct `GreasePencilDrawing` in `blender/source/blender/makesdna/DNA_grease_pencil_types.h` ([here](https://projects.blender.org/blender/blender/src/commit/4dad262dbe892e169b0caa8f6d6c6ae41a46eb02/source/blender/makesdna/DNA_grease_pencil_types.h#L100)). But what I mean with "this can be a stub for now" is that you just define `GreasePencilDrawing` using `RNA_def_struct_sdna` (see how it's done for the RNA for layers) but not add any props etc. to it. It can just be an empty container for now.

Jaime Torres commented

2024-01-30 20:37:42 +01:00

I already have a few things coded, but i'm hesitant to commit them because they don't compile as of now. One of the things i've noticed is that the functions that manage iterations in rna_def_grease_pencil.cc generally recieve a parameter by reference called CollectionPropertyIterator *iter. I'm a bit confused over this structure, and i'm not sure where this variable is coming from. An example of this structure being asked for can be seen here. As my code currently stands, I'm trying to define this kind of function for the collection property that is being defined for GreasePencilFrame, but I'm not sure where could i find the values being asked for there, this might affect our code in this specific project given we need a custom collection iterator and this might interact with it. How does this specific piece of code work?

I already have a few things coded, but i'm hesitant to commit them because they don't compile as of now. One of the things i've noticed is that the functions that manage iterations in `rna_def_grease_pencil.cc` generally recieve a parameter by reference called `CollectionPropertyIterator *iter`. I'm a bit confused over this structure, and i'm not sure where this variable is coming from. An example of this structure being asked for can be seen [here](https://projects.blender.org/blender/blender/src/commit/4dad262dbe892e169b0caa8f6d6c6ae41a46eb02/source/blender/makesrna/intern/rna_grease_pencil.cc#L156). As my code currently stands, I'm trying to define this kind of function for the collection property that is being defined for `GreasePencilFrame`, but I'm not sure where could i find the values being asked for there, this might affect our code in this specific project given we need a custom collection iterator and this might interact with it. How does this specific piece of code work?

Falk David commented

2024-01-31 10:57:14 +01:00

@mews6 Hello!
First, let me point out that it's OK to create a PR that doesn't compile yet :) Just make sure to prepend WIP: to the title. Makes it easier to see where the issue might be. It also makes it clear to others that there is work being done on this task!

Now to answer the question about the collection property. When using RNA_def_property_collection_funcs, we're defining the callbacks that can be found in the CollectionPropertyRNA struct. PropCollectionBeginFunc, PropCollectionNextFunc etc. These callbacks are called with the CollectionPropertyIterator as the first argument. It's basically the struct that manages the iteration. It keeps track of what the current item is, etc. etc.
Now in our case, I think we can mostly use the rna_iterator_array_* functions that exist already. Because we want to iterate over the sorted_keys array. So e.g. our begin callback would first call rna_iterator_array_begin with all the array information of sorted_keys. Then it would use rna_iterator_array_get to get the current item. This would be the FramesMapKey that we can pass into the frames() map to get the GreasePencilFrame. The other callbacks would works similarly. Calling the rna_iterator_array_* callback, get the key, return the frame.
Hope that helps!

EDIT: I realized that the begin callback doesn't need to return anything, so just calling rna_iterator_array_begin will be enough. But the get callback will need to get the frame. Anyway, you get the idea.

@mews6 Hello! First, let me point out that it's OK to create a PR that doesn't compile yet :) Just make sure to prepend `WIP: ` to the title. Makes it easier to see where the issue might be. It also makes it clear to others that there is work being done on this task! Now to answer the question about the collection property. When using `RNA_def_property_collection_funcs`, we're defining the callbacks that can be found in the `CollectionPropertyRNA` struct. `PropCollectionBeginFunc`, `PropCollectionNextFunc` etc. These callbacks are called with the `CollectionPropertyIterator` as the first argument. It's basically the struct that manages the iteration. It keeps track of what the current item is, etc. etc. Now in our case, I think we can mostly use the `rna_iterator_array_*` functions that exist already. Because we want to iterate over the `sorted_keys` array. So e.g. our `begin` callback would first call `rna_iterator_array_begin` with all the array information of `sorted_keys`. Then it would use `rna_iterator_array_get` to get the current item. This would be the `FramesMapKey` that we can pass into the `frames()` map to get the `GreasePencilFrame`. The other callbacks would works similarly. Calling the `rna_iterator_array_*` callback, get the key, return the frame. Hope that helps! EDIT: I realized that the `begin` callback doesn't need to return anything, so just calling `rna_iterator_array_begin` will be enough. But the `get` callback will need to get the frame. Anyway, you get the idea.

Jaime Torres referenced this issue

2024-02-18 22:52:09 +01:00

WIP: GreasePencilFrame API #116045 #118439

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

GPv3: Python API: GreasePencilFrame #116045