GPencil: SVG exporter generates wrong stroke thickness #103061

New Issue

Robert S · 2022-12-09T10:39:32+01:00

Robert S commented

2022-12-09 10:39:32 +01:00

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 526.86

Blender Version
Broken: version: 3.3.1, branch: master, commit date: 2022-10-04 18:35, hash: b292cfe5a9
Worked: (newest version of Blender that worked as expected)

Short description of error
SVG seems to allays export a single thickness, while in the Blend file there's different thicknesses.

World space lineart apparently attempts to emulate the shrinking line width of the camera angle by exporting each segment with a different line weight. This makes post processing in Illustrator/Designer/Inkscape near impossible.

Screen space lineart should then instead produce a constant line width according to the displayed line thickness. Unfortunately, with screen space on, that seems to get ignored on SVG export.

Exact steps for others to reproduce the error

Open the attached example
Export as SVG
Open SVG

lineart.blend

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 526.86 **Blender Version** Broken: version: 3.3.1, branch: master, commit date: 2022-10-04 18:35, hash: `b292cfe5a9` Worked: (newest version of Blender that worked as expected) **Short description of error** SVG seems to allays export a single thickness, while in the Blend file there's different thicknesses. World space lineart apparently attempts to emulate the shrinking line width of the camera angle by exporting each segment with a different line weight. This makes post processing in Illustrator/Designer/Inkscape near impossible. Screen space lineart should then instead produce a constant line width according to the displayed line thickness. Unfortunately, with screen space on, that seems to get ignored on SVG export. **Exact steps for others to reproduce the error** 1. Open the attached example 2. Export as SVG 3. Open SVG ![image.png](https://archive.blender.org/developer/F14046424/image.png) ![image.png](https://archive.blender.org/developer/F14046426/image.png) [lineart.blend](https://archive.blender.org/developer/F14046565/lineart.blend)

Robert S commented

2022-12-09 10:39:32 +01:00

Added subscriber: @RobertS

Omar Emara commented

2022-12-09 14:06:53 +01:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-12-09 14:06:53 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Omar Emara commented

2022-12-09 14:06:53 +01:00

I can't reproduce that, all lines have constant thickness for me. Can you attach the svg itself?

<polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." />
<polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." />
<polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." />

I can't reproduce that, all lines have constant thickness for me. Can you attach the svg itself? ``` <polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." /> <polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." /> <polyline stroke="#000000" stroke-opacity="1" fill="none" stroke-linecap="round" stroke-width="2" points="..." /> ```

Robert S commented

2022-12-09 16:38:22 +01:00

I think you misunderstood. The bug IS that the SVG has a single thickness, while in the Blend file there's two different thicknesses.

Omar Emara commented

2022-12-09 22:04:27 +01:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Germano Cavalcante commented

2022-12-12 17:29:21 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-12-12 17:29:21 +01:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Germano Cavalcante commented

2022-12-12 17:29:21 +01:00

Thickness is in pixels, and thus depends on the resolution of the final image.
It is a subject of discussion. See for example #100595 (Line Art Thickness doesn't consider Render Resolution Percentage)

But I can notice that the thicknesses are always "normalized" even with the option "Normalize" in the export settings disabled.

This happens because apparently BKE_gpencil_stroke_is_pressure_constant() always returns true.
{https://developer.blender.org/diffusion/B/browse/master/source/blender/io/gpencil/intern/gpencil_io_export_svg.cc$204-205}

I don't know if this is intentional. This seems to make the Normalize option useless.

Thickness is in pixels, and thus depends on the resolution of the final image. It is a subject of discussion. See for example #100595 (Line Art Thickness doesn't consider Render Resolution Percentage) But I can notice that the thicknesses are always "normalized" even with the option "Normalize" in the export settings disabled. This happens because apparently `BKE_gpencil_stroke_is_pressure_constant()` always returns `true`. {https://developer.blender.org/diffusion/B/browse/master/source/blender/io/gpencil/intern/gpencil_io_export_svg.cc$204-205} I don't know if this is intentional. This seems to make the Normalize option useless.

Germano Cavalcante changed title from ~~Lineart doesn't export line weights in screen space to SVG~~ to Exporter 'Grease Pencil as SVG' always normalize stroke thickness

2022-12-12 17:33:39 +01:00

Antonio Vazquez commented

2022-12-12 23:08:07 +01:00

Added subscriber: @antoniov

Antonio Vazquez commented

2022-12-12 23:08:07 +01:00

@mano-wii The normalization is done if all points of the stroke have the same pressure. This is done because the PDF export lib can handle a maximum number of thickness change and the export function tries to reduce the thickness changes. (SVG export works similar to PDF) If the pressure is equal in all points, then thickness is equal for all strokes, so I don't see a problem in the export itself, but the generated stroke... maybe LineArt is doing something to simulate the pressure change but without changing the pressure.

Antonio Vazquez commented

2022-12-12 23:14:34 +01:00

Anyway, I will take a look.

Antonio Vazquez self-assigned this 2022-12-12 23:18:48 +01:00

Antonio Vazquez commented

2022-12-12 23:39:53 +01:00

I have been testing and the scene contains 3 strokes with all points with same pressure, so the auto-normalization is correct. What I have seen is that the thickness of the strokes is 2 or 5 pixels and this is a very thin lines, so when you export the precission of the calculations to determine the thickness gets in all cases 2...if you add a Thickness modifier on top of the Lineart, you will see that all is working in SVG and PDF.

Note: I applied the Lineart modifer and separete the strokes to make easy the debug.

I have been testing and the scene contains 3 strokes with all points with same pressure, so the auto-normalization is correct. What I have seen is that the thickness of the strokes is 2 or 5 pixels and this is a very thin lines, so when you export the precission of the calculations to determine the thickness gets in all cases 2...if you add a Thickness modifier on top of the Lineart, you will see that all is working in SVG and PDF. Note: I applied the Lineart modifer and separete the strokes to make easy the debug. ![image.png](https://archive.blender.org/developer/F14054712/image.png) ![image.png](https://archive.blender.org/developer/F14054714/image.png) ![image.png](https://archive.blender.org/developer/F14054717/image.png)

Antonio Vazquez commented

2022-12-12 23:47:38 +01:00

@RobertS What is the resolution of your screen?

blender-admin commented

2022-12-13 11:39:13 +01:00

This issue was referenced by 94e7e83cd9

This issue was referenced by 94e7e83cd997170d42ddb1155814b8eda127a104

blender-admin commented

2022-12-13 11:39:13 +01:00

This issue was referenced by 85a743e08b

This issue was referenced by 85a743e08bfcaa321c7f0e7ced6bf9003a359888

Antonio Vazquez commented

2022-12-13 11:39:36 +01:00

Changed status from 'Needs Developer To Reproduce' to: 'Resolved'

Antonio Vazquez closed this issue

2022-12-13 11:39:36 +01:00

Antonio Vazquez changed title from ~~Exporter 'Grease Pencil as SVG' always normalize stroke thickness~~ to GPencil: SVG exporter generates wrong stroke thickness

2022-12-13 11:42:23 +01:00

Germano Cavalcante referenced this issue

2023-02-17 14:45:48 +01:00

3.4: Potential candidates for corrective releases #102967

Antonio Vazquez referenced this issue

2023-05-11 11:11:46 +02:00

Fix #107810: SVG exported line thickness wrong #107835

YimingWu referenced this issue from a commit

2023-05-13 16:12:04 +02:00

Fix #107810: SVG exported line thickness wrong

Sign in to join this conversation.