Grease Pencil depth merge is broken when multiple GP objects are displayed in viewport #102308

New Issue

Mathias Kærlev · 2022-11-06T19:52:38+01:00

Mathias Kærlev commented

2022-11-06 19:52:38 +01:00

System Information

Operating system: Windows 11
CPU: AMD Ryzen Threadripper 3990X
Graphics card: NVIDIA GeForce RTX 3080

Also tested on

Operating system: macOS Monterey 12.5
Machine: MacBook Pro M1 (16-inch, 2021)

Blender Version
Broken: 3.5.0 4a313b8252 2022-11-04 22:28
Also broken in 3.1.0 c77597cd0e 2022-03-08 18:16, so this is a longstanding issue.

Short description of error
Creating multiple GP objects with "Stroke Depth Order: 3D Location" causes the GP objects to reorder randomly in the viewport.
Sometimes, an object will be partially shown behind/in front of another object.
Video of the issue:
https://dl.dropboxusercontent.com/s/upg3rx1yjxdm1fy/GUsPz2Qo.webm

Exact steps for others to reproduce the error

Open the following .blend file: gp_depth_bug.blend
Rotate the view in the viewport to see how the 3 GP objects do not get rendered correctly wrt depth.

Technical exploration & possible fix
I am not well-versed in Blender internals at all, but here is my analysis:

Using RenderDoc, it appears that the depth merge pass (draw pass merge_depth_ps) does not work correctly:

Source depth texture: https://dl.dropboxusercontent.com/s/0pjjai3mz2cl8s9/4hcRr0rQ.png
Output framebuffer: https://dl.dropboxusercontent.com/s/2mtur25jmkykbf8/eSt7UkHy.png

Also, the output from the VS stage for this pass doesn't seem correct at all.
Looking at the vertex shader for this pass (gpencil_depth_merge_vert.glsl):

void main()
{
  mat4 model_matrix = mat4(gpModelMatrix[0], gpModelMatrix[1], gpModelMatrix[2], gpModelMatrix[3]);
  int v = gl_VertexID % 3;
  float x = -1.0 + float((v & 1) << 2);
  float y = -1.0 + float((v & 2) << 1);
  gl_Position = drw_view.winmat * (drw_view.viewmat * (model_matrix * vec4(x, y, 0.0, 1.0)));
}

I suspect there is an optimization going on so only the area covered by the GP object needs to have its depth merged.

However, changing this to the following seems to fix the issue (i.e. switching to a fullscreen triangle):

void main()
{
  int v = gl_VertexID % 3;
  float x = -1.0 + float((v & 1) << 2);
  float y = -1.0 + float((v & 2) << 1);
  gl_Position = vec4(x, y, 1.0, 1.0);
}

Here is a video showing the fixed depth merge pass:
https://dl.dropboxusercontent.com/s/gq33i9ofjbj9y7c/SoCkR0XU.webm

I'm sure I'm missing the full picture, but at least this fixes things for this .blend file.

**System Information** Operating system: `Windows 11` CPU: `AMD Ryzen Threadripper 3990X` Graphics card: `NVIDIA GeForce RTX 3080` Also tested on Operating system: `macOS Monterey 12.5` Machine: `MacBook Pro M1 (16-inch, 2021)` **Blender Version** Broken: 3.5.0 4a313b82529b 2022-11-04 22:28 Also broken in 3.1.0 c77597cd0e15 2022-03-08 18:16, so this is a longstanding issue. **Short description of error** Creating multiple GP objects with "Stroke Depth Order: 3D Location" causes the GP objects to reorder randomly in the viewport. Sometimes, an object will be partially shown behind/in front of another object. Video of the issue: https://dl.dropboxusercontent.com/s/upg3rx1yjxdm1fy/GUsPz2Qo.webm **Exact steps for others to reproduce the error** 1) Open the following .blend file: [gp_depth_bug.blend](https://archive.blender.org/developer/F13861970/gp_depth_bug.blend) 2) Rotate the view in the viewport to see how the 3 GP objects do not get rendered correctly wrt depth. **Technical exploration & possible fix** I am not well-versed in Blender internals at all, but here is my analysis: Using RenderDoc, it appears that the depth merge pass (draw pass `merge_depth_ps`) does not work correctly: Source depth texture: https://dl.dropboxusercontent.com/s/0pjjai3mz2cl8s9/4hcRr0rQ.png Output framebuffer: https://dl.dropboxusercontent.com/s/2mtur25jmkykbf8/eSt7UkHy.png Also, the output from the VS stage for this pass doesn't seem correct at all. Looking at the vertex shader for this pass (`gpencil_depth_merge_vert.glsl`): ``` void main() { mat4 model_matrix = mat4(gpModelMatrix[0], gpModelMatrix[1], gpModelMatrix[2], gpModelMatrix[3]); int v = gl_VertexID % 3; float x = -1.0 + float((v & 1) << 2); float y = -1.0 + float((v & 2) << 1); gl_Position = drw_view.winmat * (drw_view.viewmat * (model_matrix * vec4(x, y, 0.0, 1.0))); } ``` I suspect there is an optimization going on so only the area covered by the GP object needs to have its depth merged. However, changing this to the following seems to fix the issue (i.e. switching to a fullscreen triangle): ``` void main() { int v = gl_VertexID % 3; float x = -1.0 + float((v & 1) << 2); float y = -1.0 + float((v & 2) << 1); gl_Position = vec4(x, y, 1.0, 1.0); } ``` Here is a video showing the fixed depth merge pass: https://dl.dropboxusercontent.com/s/gq33i9ofjbj9y7c/SoCkR0XU.webm I'm sure I'm missing the full picture, but at least this fixes things for this .blend file.

Mathias Kærlev commented

2022-11-06 19:52:38 +01:00

Added subscriber: @Mathias-Kaerlev

Pratik Borhade commented

2022-11-07 06:39:56 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Pratik Borhade commented

2022-11-07 06:39:56 +01:00

Added subscribers: @antoniov, @fclem

Pratik Borhade commented

2022-11-07 06:40:00 +01:00

Added subscriber: @PratikPB2123

Miguel Pozo self-assigned this 2022-11-07 19:11:17 +01:00

Miguel Pozo commented

2022-11-08 18:07:31 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Miguel Pozo closed this issue

2022-11-08 18:07:31 +01:00

Miguel Pozo commented

2022-11-08 18:07:31 +01:00

This is an asset issue. I guess this was auto-generated from other software?

The dimensions of your environment object are (x = 511.7, y = 19708816.0, z = 6.7).
This was also causing the viewport navigation to behave incorrectly.

Selecting only the visible strokes and deleting the others results in correct behavior. gp_depth_bug.blend

This is an asset issue. I guess this was auto-generated from other software? The dimensions of your environment object are (x = 511.7, y = 19708816.0, z = 6.7). This was also causing the viewport navigation to behave incorrectly. Selecting only the visible strokes and deleting the others results in correct behavior. [gp_depth_bug.blend](https://archive.blender.org/developer/F13869396/gp_depth_bug.blend)

Miguel Pozo commented

2022-11-08 21:21:01 +01:00

Changed status from 'Resolved' to: 'Archived'

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

Grease Pencil depth merge is broken when multiple GP objects are displayed in viewport #102308