This is part of T57829.
Reduce the number of batches used to only one by shader type. This reduces GPU overhead and increase a lot the FPS. As the number of batches is small, the time to allocate and free memory was reduced in 90% or more.
Also the code has been simplified and all batch management has been removed because this is not necessary. Now, all shading groups are created after all vertex buffer data for all strokes has been created using DRW_shgroup_call_range_add().
All batch cache data has been moved to the Object runtime struct and not as before where some parts (derived data) were saved inside GPD datablock.
For particles, now the code is faster and cleaner and gets better FPS.
Thanks to Clément Foucault for his help and advices to improve speed.
The old name Instance was logic when the modifier created new object instances, but now works equal to mesh Array modifier, so the old name was not logic and must be Array.
Also added a Object to use as offset similar to mesh Array modifier.
Now it's possible to define what material is used in the generated strokes and if the strokes are put in front of the original (default) or keep the original in front.
Before, the generated strokes have been always on top of the original because they were drawn later.
This commit adds a new armature modifier for grease pencil. The deformations are done reusing the mesh deform routines.
There is also a new operator in weight paint mode to help the artist to generate weights base on armatures. This operator is required because 2D animation workflow is not equal to meshes when parent an object to armatures.
In the drawing engine has been added the option to handle the Fade object parameter used in armatures to see the strokes while move the bones.
When rename bones, all related data of grease pencil is renamed too. This not only affect new armature code, but also layers parented and hook modifiers.
Thanks @aligorith for his review and help.
Before, the weight data array was created always, but now only is added when a weight value is assigned.
This change was suggested by algorithm, and both agreed it was good idea.
The initial design assumed that there was only one object for each unique name, but that was not the case when instances were created.
Now, instances are supported and speed has been greatly improved when repetitions are used.
As a result of this change, the option to create objects has been removed in the Instances modifier. This option was strange and was also against Blender's design rules, since a modifier should never create objects. The old functionality of the modifier can be achieved with instances.
Also, several memory leakage problems that were not previously detected have been eliminated, and especially in the grid and in the drawing process
Onion Skin is not supported in multi-user datablocks. Support this, makes incompatible with instances. We need find a solution in the long term, but now it's better keep disabled and make instances work. Anyway, the new instances makes unnecessary to use muli-user datablocks.
Thanks to Charlie Jolly (mistajolly@gmail.com) for his patch D3586 that added create materials to opacity modifier.
I had to do some more changes to get all running.
