Grease Pencil Strokes visible behind solid objects #63191

New Issue

Chuck Ocheret · 2019-04-01T19:23:07+02:00

Chuck Ocheret commented

2019-04-01 19:23:07 +02:00

System Information
Operating system: Darwin-18.5.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 560X OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.8.38

Blender Version
Broken: version: 2.80 (sub 53), branch: master, commit date: 2019-04-01 14:09, hash: 9ddf0c9d38
Worked: (optional)

Short description of error
Grease Pencil Strokes visible behind solid objects. That is, within a single Grease Pencil object and you have strokes in front of and behind a solid object, you can see the strokes behind the object through the strokes in front of the object even though the object is completely opaque. This is problematic because I am trying to animate some linework on all sides of a surface of a 3D object.

Exact steps for others to reproduce the error
I am attaching a .blend file here that illustrates the problem. Later I'll describe how I created this file.
TransparentGreasePenci.blend

To observe the problem:

Open the .blend file
Observe a sphere and 2 grease pencil objects (one has blue strokes and the other has red strokes)
Rotate around the scene
Observe that through any of the blue strokes in front of the sphere you can see artifacts of the blue strokes that should be hidden behind the sphere. You cannot see any of the red strokes from the other GP object behind the sphere.

Observe that through the red strokes in front of the sphere you can see artifacts of the red strokes that should be hidden behind the sphere.

I don't know if this behavior is expected or not. While it could be a cool effect, it completely defeats the workflow I was trying to achieve or it will force me to split my Grease Pencil strokes among multiple GP objects. If I had to guess, it looks like the GP objects are rendered to a separate buffer and merged, which means they only get a single Z value to compare with other 3D geometry. Of course, I haven't looked at the code yet.

How I created the example:

Create a sphere
Create an empty Grease Pencil object
Change the material color to blue
Change the Stroke Placement to Surface
Add a mirror modifier
Draw strokes on all sides of the sphere
Observe the problem described above
Create another empty Grease Pencil Object
Change the material color to red
Change the Stroke Placement to Surface
Draw strokes on the front and back of the sphere
Observe the stroke visibility issue described above

**System Information** Operating system: Darwin-18.5.0-x86_64-i386-64bit 64 Bits Graphics card: AMD Radeon Pro 560X OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.8.38 **Blender Version** Broken: version: 2.80 (sub 53), branch: master, commit date: 2019-04-01 14:09, hash: `9ddf0c9d38` Worked: (optional) **Short description of error** Grease Pencil Strokes visible behind solid objects. That is, within a single Grease Pencil object and you have strokes in front of and behind a solid object, you can see the strokes behind the object through the strokes in front of the object even though the object is completely opaque. This is problematic because I am trying to animate some linework on all sides of a surface of a 3D object. **Exact steps for others to reproduce the error** I am attaching a .blend file here that illustrates the problem. Later I'll describe how I created this file. [TransparentGreasePenci.blend](https://archive.blender.org/developer/F6905740/TransparentGreasePenci.blend) To observe the problem: - Open the .blend file - Observe a sphere and 2 grease pencil objects (one has blue strokes and the other has red strokes) - Rotate around the scene - Observe that through any of the blue strokes in front of the sphere you can see artifacts of the blue strokes that should be hidden behind the sphere. You cannot see any of the red strokes from the other GP object behind the sphere. # Observe that through the red strokes in front of the sphere you can see artifacts of the red strokes that should be hidden behind the sphere. I don't know if this behavior is expected or not. While it could be a cool effect, it completely defeats the workflow I was trying to achieve or it will force me to split my Grease Pencil strokes among multiple GP objects. If I had to guess, it looks like the GP objects are rendered to a separate buffer and merged, which means they only get a single Z value to compare with other 3D geometry. Of course, I haven't looked at the code yet. How I created the example: - Create a sphere - Create an empty Grease Pencil object - Change the material color to blue - Change the Stroke Placement to Surface - Add a mirror modifier - Draw strokes on all sides of the sphere - Observe the problem described above - Create another empty Grease Pencil Object - Change the material color to red - Change the Stroke Placement to Surface - Draw strokes on the front and back of the sphere - Observe the stroke visibility issue described above

Chuck Ocheret commented

2019-04-01 19:23:07 +02:00

Added subscriber: @ChuckOcheret

Antonio Vazquez commented

2019-04-01 20:21:30 +02:00

Added subscriber: @antoniov

Antonio Vazquez commented

2019-04-01 20:21:30 +02:00

What mode do you have here?

Set to 3D Location. When you set to default mode (2D Layers) the strokes are visible if you put a mesh in front.

What mode do you have here? ![image.png](https://archive.blender.org/developer/F6905801/image.png) Set to 3D Location. When you set to default mode (2D Layers) the strokes are visible if you put a mesh in front.

Antonio Vazquez commented

2019-04-01 20:22:27 +02:00

Your file in 3D Location mode.

Note: Anyway, we still have a problem with alpha strokes and we are working to fix it.

Your file in 3D Location mode. ![image.png](https://archive.blender.org/developer/F6905808/image.png) Note: Anyway, we still have a problem with alpha strokes and we are working to fix it.

Chuck Ocheret commented

2019-04-01 20:27:00 +02:00

I've tried both 3D location (my current setting) as well as 2D layers with much the same effect. Even in the example you posted above, you can see the rear strokes through the sphere, but only where there are strokes in front of the sphere. The effect when animating is that the strokes in front serve as a transparency map for the sphere. Except all you can see through the sphere are the strokes from the same GP object behind it.

Antonio Vazquez commented

2019-04-01 20:29:10 +02:00

Yes, I know for alpha strokes...it's a already detected problem. Wwe are looking for a solution.

Chuck Ocheret commented

2019-04-01 20:44:05 +02:00

I just tried it with completely opaque strokes drawn with strength set to 1.0 and no pressure sensitivity. This is just to ensure that there is absolutely no transparency involved. If you look from the front (Numpad 1) you can see the that it looks like the far strokes are subtracting from the near strokes. When you look from the back (Ctrl-Numpad 1) it all looks ok.

But, if I reduce the material's stroke Alpha to, say, .5, then you still get the subtractive effect in front view but you get the transparency effect from the rear view.

I'm supplying a new .blend file that shows this. You can play with the material's stroke alpha to see the different effects.

TransparentGreasePenci1.blend

I just tried it with completely opaque strokes drawn with strength set to 1.0 and no pressure sensitivity. This is just to ensure that there is absolutely no transparency involved. If you look from the front (Numpad 1) you can see the that it looks like the far strokes are subtracting from the near strokes. When you look from the back (Ctrl-Numpad 1) it all looks ok. But, if I reduce the material's stroke Alpha to, say, .5, then you still get the subtractive effect in front view but you get the transparency effect from the rear view. I'm supplying a new .blend file that shows this. You can play with the material's stroke alpha to see the different effects. [TransparentGreasePenci1.blend](https://archive.blender.org/developer/F6905841/TransparentGreasePenci1.blend)

Sebastian Parborg commented

2019-04-02 11:30:07 +02:00

Closed as duplicate of #59425

Sebastian Parborg closed this issue

2019-04-02 11:30:07 +02:00

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Grease Pencil Strokes visible behind solid objects #63191

Observe that through the red strokes in front of the sphere you can see artifacts of the red strokes that should be hidden behind the sphere.