Mesh to Volume node inconsistent with concave corners #127129

New Issue

Harry McKenzie · 2024-09-04T03:51:16+02:00

Harry McKenzie commented

2024-09-04 03:51:16 +02:00

System Information
Operating system: Windows-10-10.0.22621-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX TITAN/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 474.30

Blender Version
Broken: version: 4.2.0, branch: blender-v4.2-release, commit date: 2024-07-16 06:20, hash: a51f293548ad
Worked: Never

Short description of error
When you add a Mesh to Volume node to a perfectly 90-degree shape, like this T-shaped example, it results in excess volume on one concave corner, which is not consistent with the other concave corner. In the image, the original cuboid shape is shown from a top view on the left, with two faces extruded in opposite directions, forming a T-shaped cuboid. One object is then applied with a Mesh to Volume density of 1.0, and the other with a density of 50.0 to exaggerate the volume effect, making the problem more apparent.

Exact steps for others to reproduce the error
Add a plane and subdivide it once, then remove half of it. Extrude along the Z axis, then extrude one face perpendicularly in opposite directions to achieve the shape shown in the screenshot. Next, add a Geometry Node modifier, and then add a Mesh to Volume node. Set the density to 50.0.

**System Information** Operating system: Windows-10-10.0.22621-SP0 64 Bits Graphics card: NVIDIA GeForce GTX TITAN/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 474.30 **Blender Version** Broken: version: 4.2.0, branch: blender-v4.2-release, commit date: 2024-07-16 06:20, hash: `a51f293548ad` Worked: Never **Short description of error** When you add a Mesh to Volume node to a perfectly 90-degree shape, like this T-shaped example, it results in excess volume on one concave corner, which is not consistent with the other concave corner. In the image, the original cuboid shape is shown from a top view on the left, with two faces extruded in opposite directions, forming a T-shaped cuboid. One object is then applied with a Mesh to Volume density of 1.0, and the other with a density of 50.0 to exaggerate the volume effect, making the problem more apparent. <img width="1021" alt="image" src="attachments/6a677781-7ba7-48c0-b041-d02e95e46093"> **Exact steps for others to reproduce the error** Add a plane and subdivide it once, then remove half of it. Extrude along the Z axis, then extrude one face perpendicularly in opposite directions to achieve the shape shown in the screenshot. Next, add a Geometry Node modifier, and then add a Mesh to Volume node. Set the density to 50.0. <img width="798" alt="image" src="attachments/bc4c2935-792b-48dc-a0eb-459753460867">

image.png

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image.png

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Harry McKenzie added the

labels 2024-09-04 03:51:17 +02:00

YimingWu commented

2024-09-04 05:52:30 +02:00

I'd say this is generally expected since volume is represented as voxels and densities are decided on sampling the mesh. So you will always get a little bit more "smoothing" effect, especially when voxel size is big. See the file below for an example.

volume.blend

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Harry McKenzie commented

2024-09-04 06:09:01 +02:00

I'd say this is generally expected since volume is represented as voxels and densities are decided on sampling the mesh. So you will always get a little bit more "smoothing" effect, especially when voxel size is big. See the file below for an example.

Thank you for your response. The thing is, it is inconsistent, should it not be the same for "same" corners, why would it appear differently in both corners? That is quite confusing. The thing is it will create a problem like this one here and there is no solution. https://blender.stackexchange.com/questions/323847/mesh-to-volume-node-rounding-concave-corners-causes-unwanted-excess-blocks

> I'd say this is generally expected since volume is represented as voxels and densities are decided on sampling the mesh. So you will always get a little bit more "smoothing" effect, especially when voxel size is big. See the file below for an example. Thank you for your response. The thing is, it is inconsistent, should it not be the same for "same" corners, why would it appear differently in both corners? That is quite confusing. The thing is it will create a problem like this one here and there is no solution. https://blender.stackexchange.com/questions/323847/mesh-to-volume-node-rounding-concave-corners-causes-unwanted-excess-blocks

YimingWu commented

2024-09-04 06:21:43 +02:00

Well if you move the mesh in edit mode, you will see that the corner treatment would change depending on how it lands on the voxel border, so it's not really "only one corner shows the effect". Sometimes it's both, sometimes you will have concave corners eaten as well. A way to minimize the effect is simply reduce the voxel size.

Do you have a specific use case where pin-accurate volume boundary from mesh is required? In which case would a volume absorption/scatter shader on the mesh be a viable option?

Well if you move the mesh in edit mode, you will see that the corner treatment would change depending on how it lands on the voxel border, so it's not really "only one corner shows the effect". Sometimes it's both, sometimes you will have concave corners eaten as well. A way to minimize the effect is simply reduce the voxel size. Do you have a specific use case where pin-accurate volume boundary from mesh is required? In which case would a volume absorption/scatter shader on the mesh be a viable option?

Iliya Katushenock commented

2024-09-04 06:52:31 +02:00

Thanks for the report, but the issue reported here is a request for modified/improved behavior and not a bug in current behavior. Closing as this bug tracker is only for bugs and errors.

For user requests and feedback, please use other channels: https://developer.blender.org/docs/handbook/communication/user_feedback/

For more information on why this isn't considered a bug, visit: https://developer.blender.org/docs/handbook/bug_reports/not_a_bug/

Thanks for the report, but the issue reported here is a request for modified/improved behavior and not a bug in current behavior. Closing as this bug tracker is only for bugs and errors. For user requests and feedback, please use other channels: https://developer.blender.org/docs/handbook/communication/user_feedback/ For more information on why this isn't considered a bug, visit: https://developer.blender.org/docs/handbook/bug_reports/not_a_bug/

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Iliya Katushenock closed this issue

2024-09-04 06:52:35 +02:00

Blender Bot added

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labels 2024-09-04 06:52:35 +02:00

Harry McKenzie commented

2024-09-04 07:13:32 +02:00

@ChengduLittleA Thank you for looking into this; your time is highly appreciated. You are correct that reducing the voxel size will help, but unfortunately, it would only work for certain meshes, while it would break for others with different voxel sizes. If the voxel size were disconnected and manually reduced, it could theoretically be adjusted for a specific mesh, but it would then cause issues for other meshes. As it is currently configured, this setup works for every mesh. Disconnecting it would only work for certain meshes, as it would no longer be in sync with the entire setup. Do you have any ideas on how to work around this? This is the blend https://blend-exchange.com/b/kB3920y5/

@ChengduLittleA Thank you for looking into this; your time is highly appreciated. You are correct that reducing the voxel size will help, but unfortunately, it would only work for certain meshes, while it would break for others with different voxel sizes. If the voxel size were disconnected and manually reduced, it could theoretically be adjusted for a specific mesh, but it would then cause issues for other meshes. As it is currently configured, this setup works for every mesh. Disconnecting it would only work for certain meshes, as it would no longer be in sync with the entire setup. Do you have any ideas on how to work around this? This is the blend https://blend-exchange.com/b/kB3920y5/ <img width="944" alt="image" src="attachments/306dc609-1c88-49ee-8a85-8bbf09dffe5e">

image.png

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Mesh to Volume node inconsistent with concave corners #127129