GreasePencil Merge Planning #54721

New Issue

Joshua Leung · 2018-04-19T11:19:22+02:00

Joshua Leung commented

2018-04-19 11:19:22 +02:00

Meeting between Bastien, Campbell, Dalai, Joshua, William to review GP Branch and discuss what's needed to get it merged into 2.8.

Meeting Notes: 18/4/2018 GP Branch to 2.8 Merge Meeting Notes 20180418.pdf

GP Branch Mega-Patch: D2889

Meeting between Bastien, Campbell, Dalai, Joshua, William to review GP Branch and discuss what's needed to get it merged into 2.8. Meeting Notes: *18/4/2018* [GP Branch to 2.8 Merge Meeting Notes 20180418.pdf](https://archive.blender.org/developer/F2836205/GP_Branch_to_2.8_Merge_Meeting_Notes_20180418.pdf) GP Branch Mega-Patch: [D2889](https://archive.blender.org/developer/D2889)

Joshua Leung self-assigned this 2018-04-19 11:19:22 +02:00

Joshua Leung commented

2018-04-19 11:19:22 +02:00

Added subscriber: @JoshuaLeung

Antonio Vazquez commented

2018-04-19 17:20:48 +02:00

Added subscriber: @antoniov

Antonio Vazquez commented

2018-04-19 17:20:48 +02:00

As first step, I'm going to remove the palettecolor pointer from bGPDstroke struct.

Dalai Felinto changed title from ~~GP Merge Meeting - 2018/4/18~~ to GreasePencil Merge Planning

2018-04-20 15:54:34 +02:00

Antonio Vazquez commented

2018-04-20 18:15:23 +02:00

I have removed from DNA any reference to PaletteColor pointer.

Antonio Vazquez commented

2018-04-20 18:24:59 +02:00

About the concerns with modifiers (not VFX) there were several reasons that justify our past design decisions.

The object modifier list is already developed and we can reuse all system to copy, enable, disable, link, etc. What is the reason to duplicate code to do the same? Are not modifiers for grease pencil strokes what we have today? From user point of view, what is different in grease pencil modifiers of 3D modifiers?
Currently, there are 3D modifiers used only for some object types, for example we cannot add a particle modifier to curve. The filter to be able to use one modifier for one object type is defined in ModifierTypeType enum. For grease pencil we have added a new type eModifierTypeType_Gpencil, so we don't use any hack or special code for this, just enable this flag in modifier definition.
To define the data that can be used in modifier, there is a definition in ModifierTypeFlag enum. Here again we have added a new flag type eModifierTypeFlag_GpencilMod, and again here no special code or hack.
About reuse 3D modifiers for grease pencil, there is one big difference between 3D objects and grease pencil object. 3D objects use mesh data, grease pencil uses strokes.
This is not a small difference. Usually, in a 3D object there is a group of points that create a shape. The number of points usually doesn't change, it's their position what change or animate.

On the other side, the stroke data changes by layer and frame, so the points of one stroke for frame 1 are not the same of frame 2, and maybe there are a different number of strokes. We never animate the points of a stroke, the artist creates a new stroke.

The solution used was to define a set of callbacks to the ModifierTypeInfo struct with the required functions for grease pencil. The main difference is that these callbacks receive strokes, not meshes, but the main idea is the same used for meshes, nothing different.

There are more differences with grease pencil modifiers; they can change the shape, the points or the color of the strokes. If we want change the color what would we use? A material modifier? This is not possible because a modifier at material level will override the material for all strokes, but maybe we want change only some strokes of same grease pencil layer.

As final main point against reuse the same modifiers for 3D and GP, the grease pencil objects can be filtered by grease pencil layer, and this is something that we haven't in 3D. We must remember here that grease pencil is a 2D environment in a 3D environment.

Now the modifiers are using a custom copy on write system. When grease pencil was created the standard COW was not ready, so we decided create a custom one.

Every time the frame changes, or the drawing cache is dirty, a fresh copy of the current frame data is done and modifiers applied. Now the custom copy on write system only evaluates current frame and this reduce the overhead.

I'm not against using standard COW, but we would have to test the speed of the system. The grease pencil data can change a lot very fast while the user is drawing or doing edition, and execute a full COW of all data can be very slow (the data could be 10 GP layers, with 50 frames each , with 200 strokes each with an average of 50 points T = 10 * 50 * 200 * 50)

About the concerns with modifiers (not VFX) there were several reasons that justify our past design decisions. 1) The object modifier list is already developed and we can reuse all system to copy, enable, disable, link, etc. What is the reason to duplicate code to do the same? Are not modifiers for grease pencil strokes what we have today? From user point of view, what is different in grease pencil modifiers of 3D modifiers? 2) Currently, there are 3D modifiers used only for some object types, for example we cannot add a particle modifier to curve. The filter to be able to use one modifier for one object type is defined in *ModifierTypeType* enum. For grease pencil we have added a new type e*ModifierTypeType_Gpencil*, so we don't use any hack or special code for this, just enable this flag in modifier definition. 3) To define the data that can be used in modifier, there is a definition in *ModifierTypeFlag* enum. Here again we have added a new flag type *eModifierTypeFlag_GpencilMod*, and again here no special code or hack. 4) About reuse 3D modifiers for grease pencil, there is one big difference between 3D objects and grease pencil object. 3D objects use mesh data, grease pencil uses strokes. This is not a small difference. Usually, in a 3D object there is a group of points that create a shape. The number of points usually doesn't change, it's their position what change or animate. On the other side, the stroke data changes by layer and frame, so the points of one stroke for frame 1 are not the same of frame 2, and maybe there are a different number of strokes. We never animate the points of a stroke, the artist creates a new stroke. The solution used was to define a set of callbacks to the ModifierTypeInfo struct with the required functions for grease pencil. The main difference is that these callbacks receive strokes, not meshes, but the main idea is the same used for meshes, nothing different. There are more differences with grease pencil modifiers; they can change the shape, the points or the color of the strokes. If we want change the color what would we use? A material modifier? This is not possible because a modifier at material level will override the material for all strokes, but maybe we want change only some strokes of same grease pencil layer. As final main point against reuse the same modifiers for 3D and GP, the grease pencil objects can be filtered by grease pencil layer, and this is something that we haven't in 3D. We must remember here that grease pencil is a 2D environment in a 3D environment. 5) Now the modifiers are using a custom copy on write system. When grease pencil was created the standard COW was not ready, so we decided create a custom one. Every time the frame changes, or the drawing cache is dirty, a fresh copy of the current frame data is done and modifiers applied. Now the custom copy on write system only evaluates current frame and this reduce the overhead. I'm not against using standard COW, but we would have to test the speed of the system. The grease pencil data can change a lot very fast while the user is drawing or doing edition, and execute a full COW of all data can be very slow (the data could be 10 GP layers, with 50 frames each , with 200 strokes each with an average of 50 points T = 10 * 50 * 200 * 50)

Dalai Felinto commented

2018-04-23 13:19:56 +02:00

Changed status from 'Open' to: 'Resolved'

Dalai Felinto closed this issue

2018-04-23 13:19:56 +02:00

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GreasePencil Merge Planning #54721