Grease Pencil Ignores 'Stroke Placement: Stroke' #81950

New Issue

Dong-Hyun Kim · 2020-10-22T10:02:12+02:00

Dong-Hyun Kim commented

2020-10-22 10:02:12 +02:00

System Information
Operating system: Windows 10 64-bit 2004
Graphics card: NVIDIA Geforce 2070 Super
CPU: AMD Ryzen 7 3700X (8-core)

Blender Version
Broken: example: 2.90.1, master
Broken: 2.83.0
Worked: 2.82a
Caused by 29f3af9527

Short description of error
Grease Pencil Ignores Stroke Placement: Stroke
It Just behaves like Stroke Placement: 3D Cursor (When 3D cursor is closer to the viewpoint than the base stroke)
or partially behaves like Stoke Placement: 3D Cursor (When 3D cursor is farther from the viewpoint than the base stroke).

Exact steps for others to reproduce the error
I tried my best to describe it clearly in the video.
To summarize, You only have to draw strokes in the 3D space and try Stroke Placement: Stroke.

This is from 2.80
GP Stroke Placement on 2.80.mp4

And This is from 2.90.1
GP Stroke Placement on 2.90.1.mp4

**System Information** Operating system: Windows 10 64-bit 2004 Graphics card: NVIDIA Geforce 2070 Super CPU: AMD Ryzen 7 3700X (8-core) **Blender Version** Broken: example: 2.90.1, master Broken: 2.83.0 Worked: 2.82a Caused by 29f3af9527 **Short description of error** Grease Pencil Ignores **Stroke Placement: Stroke** It Just behaves like **Stroke Placement: 3D Cursor** (When 3D cursor is closer to the viewpoint than the base stroke) or partially behaves like **Stoke Placement: 3D Cursor** (When 3D cursor is farther from the viewpoint than the base stroke). **Exact steps for others to reproduce the error** I tried my best to describe it clearly in the video. To summarize, You only have to draw strokes in the 3D space and try **Stroke Placement: Stroke**. This is from 2.80 [GP Stroke Placement on 2.80.mp4](https://archive.blender.org/developer/F9033314/GP_Stroke_Placement_on_2.80.mp4) And This is from 2.90.1 [GP Stroke Placement on 2.90.1.mp4](https://archive.blender.org/developer/F9033315/GP_Stroke_Placement_on_2.90.1.mp4)

blender-admin commented

2020-10-22 10:02:12 +02:00

#81927 was marked as duplicate of this issue

Dong-Hyun Kim commented

2020-10-22 10:02:13 +02:00

Added subscriber: @temeddix

Dong-Hyun Kim changed title from ~~Grease Pencil Ignores 'Stroke Placement as Stroke'~~ to Grease Pencil Ignores 'Stroke Placement: Stroke'

2020-10-22 11:04:54 +02:00

Philipp Oeser commented

2020-10-22 16:12:02 +02:00

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

Philipp Oeser commented

2020-10-22 16:15:47 +02:00

Added subscribers: @Lovely_Bigga, @lichtwerk

Antonio Vazquez commented

2020-10-22 16:40:59 +02:00

Added subscribers: @fclem, @antoniov

Antonio Vazquez commented

2020-10-22 16:40:59 +02:00

@lichtwerk The code is using ED_view3d_autodist_depth()and ED_view3d_autodist_depth_seg() and this was not changed in the refactor (this is old code). I don't know if these functions are working as expected. @fclem any clue?

@lichtwerk The code is using `ED_view3d_autodist_depth()`and `ED_view3d_autodist_depth_seg()` and this was not changed in the refactor (this is old code). I don't know if these functions are working as expected. @fclem any clue?

gabriel montagné commented

2020-11-02 00:35:43 +01:00

Added subscriber: @GabrielMontagne

Suvidh khasgiwala commented

2020-11-11 18:46:21 +01:00

Has this issue been fixed? I need to work with grease pencil every day and every day I face this issue.

Philipp Oeser commented

2020-11-17 16:06:12 +01:00

Dare setting this to High (since the feature is basically broken)

gabriel montagné commented

2020-11-17 16:11:18 +01:00

In #81950#1056356, @lichtwerk wrote:
Dare setting this to High (since the feature is basically broken)

... and it invalidates, for example, all the training anyone is using about how to use GP.

> In #81950#1056356, @lichtwerk wrote: > Dare setting this to High (since the feature is basically broken) ... and it invalidates, for example, all the training anyone is using about how to use GP.

Clément Foucault commented

2020-11-17 17:25:48 +01:00

I'm going to bisect to find the bad commit.

Philipp Oeser commented

2020-11-17 17:34:02 +01:00

Broke between eed1beff88 and fa823f0af8 probably 29f3af9527

Broke between eed1beff88 and fa823f0af8 probably 29f3af9527

Philipp Oeser commented

2020-11-17 18:57:57 +01:00

Maybe #78574 (GPencil: Z pass combine not work ) is related?

Clément Foucault commented

2020-11-17 20:59:35 +01:00

Yes i can confirm the bad commit is 29f3af9527.

Yes i can confirm the bad commit is 29f3af9527.

Dalai Felinto commented

2020-11-18 10:35:36 +01:00

Added subscriber: @dfelinto

Dalai Felinto commented

2020-11-18 10:35:36 +01:00

Since this is broken since March I'm tagging as 2.92 to free 2.91 to move to bcon4 regardless of this. That said a fix for this would still be welcome in 2.91 if done in time.

Jamell Moore commented

2020-11-29 21:42:53 +01:00

Added subscriber: @JamellMoore

Jamell Moore commented

2020-11-29 21:42:53 +01:00

Hi all. Thanks for working so hard on a fantastic tool. I'm a new developer here. I've been dabbling with programming and computer graphics for years now as a hobbyist but now have realized graphics programming is what I really want to do as a career. The fact that Blender is open source gives me a good opportunity to gain some experience and develop my skills.

I was reviewing the GPencil code to try to improve on how the brush size could be presented to the user and handled internally but I thought it would be better to help fix bugs first, where I can.

My findings regarding this bug

When drawing a stroke with the gpencil draw tool and the greasepencil_stroke_placement_view3d setting set to 'surface' or 'stroke', a new stroke is made that interpolates between the points that hit a surface/stroke.
When drawing a stroke, a check is made around each buffer point to see if it is over existing strokes by reading the depth values within the depth buffer. If depth isn't found around the point the point isn't over an existing stroke. It is then invalidated. The draw tool with stroke placement set to stroke only wants to interpolate between points that hit existing strokes.
When checking for depth around the stroke area by indirectly calling view3d_opengl_read_Z_pixels some of the depths have values of approx 0.99 (Near the far plane) if stroke placement is 'stroke'. This is NOT THE EXPECTED RESULT. All points that projected into the background should have a depth value of 1.0 in the z-buffer.
I ran a test by setting the depth values to 0.5 (arbitrary) in the gpencil_frag.glsl shader and recorded the values around a single point: when view3d_opengl_read_Z_pixels is called. Values around the point were 0.5. This indicated that the drawn stroke was drawn to the depth buffer before depth tests can be carried out.
I looked at the previous implementation and found that when do_fast_drawing is enabled, in the gpencil engine, the current view is frozen and the paint stroke is drawn in a different pass without recording depth. This is possible because the view is stationary whilst a stroke is drawn.
In the new implementation do_fast_drawing is never enabled. On Line 262: gpencil_engine.c it reads pd->do_fast_drawing = false; /* TODO option */. If this is set to true the stroke placement feature works. See video.

Fix-#81950-GPencil-Stroke-Placement-Solution-VID-01.mp4

So my question now is - is fast_drawing feature fully implemented in its current state, so that we can test and commit this change?

Hi all. Thanks for working so hard on a fantastic tool. I'm a new developer here. I've been dabbling with programming and computer graphics for years now as a hobbyist but now have realized graphics programming is what I really want to do as a career. The fact that Blender is open source gives me a good opportunity to gain some experience and develop my skills. I was reviewing the GPencil code to try to improve on how the brush size could be presented to the user and handled internally but I thought it would be better to help fix bugs first, where I can. **My findings regarding this bug** 1. When drawing a stroke with the gpencil draw tool and the greasepencil_stroke_placement_view3d setting set to 'surface' or 'stroke', a new stroke is made that interpolates between the points that hit a surface/stroke. 2. When drawing a stroke, a check is made around each buffer point to see if it is over existing strokes by reading the depth values within the depth buffer. If depth isn't found around the point the point isn't over an existing stroke. It is then invalidated. The draw tool with stroke placement set to stroke only wants to interpolate between points that hit existing strokes. 3. When checking for depth around the stroke area by indirectly calling view3d_opengl_read_Z_pixels some of the depths have values of approx 0.99 (Near the far plane) if stroke placement is 'stroke'. This is NOT THE EXPECTED RESULT. All points that projected into the background should have a depth value of 1.0 in the z-buffer. 4. I ran a test by setting the depth values to 0.5 (arbitrary) in the gpencil_frag.glsl shader and recorded the values around a single point: when view3d_opengl_read_Z_pixels is called. Values around the point were 0.5. This indicated that the drawn stroke was drawn to the depth buffer before depth tests can be carried out. 5. I looked at the previous implementation and found that when do_fast_drawing is enabled, in the gpencil engine, the current view is frozen and the paint stroke is drawn in a different pass without recording depth. This is possible because the view is stationary whilst a stroke is drawn. 6. In the new implementation do_fast_drawing is never enabled. On Line 262: gpencil_engine.c it reads `pd->do_fast_drawing = false; /* TODO option */`. If this is set to true the stroke placement feature works. See video. [Fix-#81950-GPencil-Stroke-Placement-Solution-VID-01.mp4](https://archive.blender.org/developer/F9409508/Fix-#81950-GPencil-Stroke-Placement-Solution-VID-01.mp4) So my question now is - is fast_drawing feature fully implemented in its current state, so that we can test and commit this change?

Antonio Vazquez commented

2020-11-30 16:29:34 +01:00

Fast Drawing was developed as Plan B, but never was enabled. Our plan is to remove this feature if it's not required, so enable this is not the solution. Anyway, @fclem can give you a better answer than me.

Fast Drawing was developed as `Plan B`, but never was enabled. Our plan is to remove this feature if it's not required, so enable this is not the solution. Anyway, @fclem can give you a better answer than me.

Jamell Moore commented

2020-11-30 16:55:32 +01:00

Thanks Antonio. I will look into this further and wait for more information from Clement.

Sorry about the diff. I had just pushed it as you responded.

Thanks Antonio. I will look into this further and wait for more information from Clement. Sorry about the diff. I had just pushed it as you responded.

Jamell Moore commented

2020-11-30 18:57:21 +01:00

I just wanted to clarify my original findings so that I don't cause confusion for anyone else who is looking into this. There was a small mistake.

I have tested this in 2.82.7 where the feature is working correctly. In this version I have followed the execution path and fast drawing is definitely enabled with the GP_DRW_PAINT_PAINTING flag. The do_fast_drawing flag doesn't exist in this version.

That being said I have since found that the in 2.82.7 the following is used in gpencil_engine.c to check whether the draw call is for depth.

/* if the draw is for select, do a basic drawing and return */
  if (DRW_state_is_select() || DRW_state_is_depth()) {
    drw_gpencil_select_render(stl, psl);
    return;
  }

With this commented out the feature breaks so I believe this needs to be reimplemented in some way. Despite the name drw_gpencil_select_render handles the drawing for depth test passes also.

I just wanted to clarify my original findings so that I don't cause confusion for anyone else who is looking into this. There was a small mistake. I have tested this in 2.82.7 where the feature is working correctly. In this version I have followed the execution path and fast drawing is definitely enabled with the GP_DRW_PAINT_PAINTING flag. The do_fast_drawing flag doesn't exist in this version. That being said I have since found that the in 2.82.7 the following is used in gpencil_engine.c to check whether the draw call is for depth. ``` /* if the draw is for select, do a basic drawing and return */ if (DRW_state_is_select() || DRW_state_is_depth()) { drw_gpencil_select_render(stl, psl); return; } ``` With this commented out the feature breaks so I believe this needs to be reimplemented in some way. Despite the name drw_gpencil_select_render handles the drawing for depth test passes also.

Jamell Moore commented

2020-12-03 19:47:24 +01:00

I was a bit hasty with my previous diagnosis but I believe my current diff has solved the problem without introducing any other problems. I believe the depth_only_fb is intended for doing partial depth tests so the stroke buffers just needed to be excluded from the depth only draw calls.

Question: Have there been any thoughts about caching the results of the depths whilst drawing each stroke? If so how would you go about it?

I was a bit hasty with my previous diagnosis but I believe my current diff has solved the problem without introducing any other problems. I believe the depth_only_fb is intended for doing partial depth tests so the stroke buffers just needed to be excluded from the depth only draw calls. Question: Have there been any thoughts about caching the results of the depths whilst drawing each stroke? If so how would you go about it?

blender-admin commented

2020-12-08 16:48:11 +01:00

This issue was referenced by 5b73083d4f

This issue was referenced by 5b73083d4f207690e89f3a8863480de2bb4df24d

Antonio Vazquez commented

2020-12-08 16:50:30 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Antonio Vazquez closed this issue

2020-12-08 16:50:30 +01:00

Antonio Vazquez self-assigned this 2020-12-08 16:50:30 +01:00

Thomas Dinges added this to the 2.92 milestone 2023-02-08 16:16:03 +01:00

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Grease Pencil Ignores 'Stroke Placement: Stroke' #81950