Eevee: Transparent material black parts #64962

New Issue

Marco · 2019-05-21T23:12:20+02:00

Marco commented

2019-05-21 23:12:20 +02:00

System Information
Operating system: Ubuntu 18.04.2
Graphics card: AMD RX 580

Blender Version
Broken: 2.80.71, e787700393, 2019-05-20

Short description of error
I have this mesh with some transparent parts, in Eevee with Alpha Hashed as Blend Mode i get these weird black parts in the distance.
Same result with Alpha Clip, for the Alpha Blend it gets all blown out.

Simplified blend
Clouds issue.blend

**System Information** Operating system: Ubuntu 18.04.2 Graphics card: AMD RX 580 **Blender Version** Broken: 2.80.71, e78770039397, 2019-05-20 **Short description of error** I have this mesh with some transparent parts, in Eevee with Alpha Hashed as Blend Mode i get these weird black parts in the distance. Same result with Alpha Clip, for the Alpha Blend it gets all blown out. ![Screenshot.jpg](https://archive.blender.org/developer/F7058965/Screenshot.jpg) Simplified blend [Clouds issue.blend](https://archive.blender.org/developer/F7063203/Clouds_issue.blend)

Marco commented

2019-05-21 23:12:20 +02:00

Added subscriber: @nacioss

Marco changed title from ~~Transparent material black parts~~ to Eevee: Transparent material black parts

2019-05-22 00:16:30 +02:00

Clément Foucault was assigned by Marco

2019-05-22 00:16:30 +02:00

Juan Gea commented

2019-05-22 01:20:03 +02:00

Added subscriber: @juang3d

Juan Gea commented

2019-05-22 01:20:03 +02:00

same problem here, black spots at the long distance

Leon Eckardt commented

2019-05-22 19:12:14 +02:00

Added subscriber: @Leon95

Leon Eckardt commented

2019-05-22 19:12:14 +02:00

Clouds issue_minimal.blend
Simplified Version, 90% of Nodes Removed

[Clouds issue_minimal.blend](https://archive.blender.org/developer/F7061275/Clouds_issue_minimal.blend) Simplified Version, 90% of Nodes Removed

Leon Eckardt commented

2019-05-22 19:13:59 +02:00

Removed subscriber: @Leon95

Clément Foucault commented

2019-05-23 16:57:21 +02:00

Changed status from 'Open' to: 'Archived'

Clément Foucault closed this issue

2019-05-23 16:57:21 +02:00

Clément Foucault commented

2019-05-23 16:57:21 +02:00

TL,DR: Well this is a float precision issue. the view range is really high and using multiple mesh layers close to each other makes the rendering bogus.

Workarounds:

use other blend modes.
use more reasonable clipping values.
Make the planes much more distant from each others.

Technical explanation:

The alpha hash blend modes operate in 2 passes. One pass that only write depth when the alpha is above the noise threshold, and one pass to write the color.
The mix node does a premultiplication of the radiance of each incomming BRDF and unpremult before the output. This makes the totally transparent regions totally black (in radiance).
The issue when there is depth fighting is that the 2nd layer is writting this black radiance on top of the previous layer because the depth test is still true (because both layers shares the same depth).

This could be solved by bypassing the depth prepass for theses objects but then we loose the benefits of the alpha hashed technique. I plan to introduce such feature (exclude from depth prepass) but for 2.80 it is not possible.

TL,DR: Well this is a float precision issue. the view range is really high and using multiple mesh layers close to each other makes the rendering bogus. Workarounds: - use other blend modes. - use more reasonable clipping values. - Make the planes much more distant from each others. Technical explanation: - The alpha hash blend modes operate in 2 passes. One pass that only write depth when the alpha is above the noise threshold, and one pass to write the color. - The mix node does a premultiplication of the radiance of each incomming BRDF and unpremult before the output. This makes the totally transparent regions totally black (in radiance). - The issue when there is depth fighting is that the 2nd layer is writting this black radiance on top of the previous layer because the depth test is still true (because both layers shares the same depth). This could be solved by bypassing the depth prepass for theses objects but then we loose the benefits of the alpha hashed technique. I plan to introduce such feature (exclude from depth prepass) but for 2.80 it is not possible.

Marco commented

2019-05-23 17:04:18 +02:00

Thank you a lot for all the info Clement ;) you are doing an amazing job.

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Eevee: Transparent material black parts #64962