Unexplained reflection logic (artifacts) on water shader with bump mapping #98869

New Issue

Sebastien Larocque · 2022-06-14T02:41:06+02:00

2022-06-14 02:41:06 +02:00

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.59

Blender Version
Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: e05e1e3691
Worked: Probably never

Short description of error
Unexplained reflection logic (artifacts) on water shader with bump mapping.

Exact steps for others to reproduce the error

Open the sample project in attachment.
Test the rendering in Cycles in the viewport.
Test the different shaders (Shading tab) with the tests cases in the object “Water_Large” in the “Water” collection.
Try to vary the height of the camera from 0 meter to many meters to see how it affects the artifacts.
You can also enable the “Test - Torus” collection for extra testing.

The object “Water_Large_SimpleReflection” shows the result without any bump mapping. The reflection is accurate. The object “Water_Large” shows the result with bump mapping applied. Naturally, the reflection is distorted because of the angle of the waves created on the reflection. That is normal, but the reflection of a portion of the rectangles is offset with wrong placement.

The problem:
For a reason that I really cannot explain, the rectangles of 45 degrees are reflected vertically on the water surface from a precise horizontal position. Without expecting perfection, the reflection should have been displayed with an average of 45 degrees on the water. It is like a threshold where the reflection logic changes See the screenshot and check where the red arrow is for an indication.

On the screenshot “Camera 1 - 2 meters high”, we can see the reflection making a steep angle at a precise horizontal position on the water.
On the screenshot “Camera 2 - 20 meters high”, we can see the problem not being as present as on camera 1. There are still some artifacts.

Observations:

The problem tends to disappear as we increase the camera distance from the water surface.
Furthermore, the problem is less apparent when the noise scale of the texture node used to create the height factor of the bump mapping is lower. You can play with the parameters of the “Water" shader.
The objects closer to the camera are lower in the image height and also show are a more natural reflection (the rectangle at the right for example).

As you can see on the screenshots, a part of the far objects is being reflected correctly on the water surface, but the majority of the color is not aligned with the angle of the object. Strangely, the objects are being reflected at 45 degrees from the far horizon line and suddenly, from a virtual horizontal line, they start reflecting vertically as if the objects were totally vertical. And that happens at a precise vertical height on the water surface. This is exactly where the problem happens.

For years, I have never seen any issues with reflections. If you have a scene with a city skyline in the horizon, you are less likely to see that kind of artifacts. In the present case, we have the equivalent of skyscrapers, but at 45 degrees.

I also tried with Blender version 2.93 and the problem is the same.

Before reporting this bug, I looked at the scene setup. To validate the nature of the problem, I decided to take into account the following factors.

The bump height and the distance are relatively low. Nothing exaggerated here to mess up the results.
The height of the camera is at 2 meters from the water surface, which is about the height of a human. Nothing exaggerated once again.

I was not sure if that was a bug in Cycles or a limitation. I relied on the definition that has been given to me, “if it works as expected”, and clearly it is not working as expected. Therefore, I decided to report it.

ReflectionBug.blend

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.59 **Blender Version** Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: `e05e1e3691` Worked: Probably never **Short description of error** Unexplained reflection logic (artifacts) on water shader with bump mapping. **Exact steps for others to reproduce the error** * Open the sample project in attachment. * Test the rendering in Cycles in the viewport. * Test the different shaders (Shading tab) with the tests cases in the object “Water_Large” in the “Water” collection. * Try to vary the height of the camera from 0 meter to many meters to see how it affects the artifacts. * You can also enable the “Test - Torus” collection for extra testing. The object “Water_Large_SimpleReflection” shows the result without any bump mapping. The reflection is accurate. The object “Water_Large” shows the result with bump mapping applied. Naturally, the reflection is distorted because of the angle of the waves created on the reflection. That is normal, but the reflection of a portion of the rectangles is offset with wrong placement. **The problem:** For a reason that I really cannot explain, the rectangles of 45 degrees are reflected vertically on the water surface from a precise horizontal position. Without expecting perfection, the reflection should have been displayed with an average of 45 degrees on the water. It is like a threshold where the reflection logic changes See the screenshot and check where the red arrow is for an indication. * On the screenshot “Camera 1 - 2 meters high”, we can see the reflection making a steep angle at a precise horizontal position on the water. * On the screenshot “Camera 2 - 20 meters high”, we can see the problem not being as present as on camera 1. There are still some artifacts. **Observations:** * The problem tends to disappear as we increase the camera distance from the water surface. * Furthermore, the problem is less apparent when the noise scale of the texture node used to create the height factor of the bump mapping is lower. You can play with the parameters of the “Water" shader. * The objects closer to the camera are lower in the image height and also show are a more natural reflection (the rectangle at the right for example). As you can see on the screenshots, a part of the far objects is being reflected correctly on the water surface, but the majority of the color is not aligned with the angle of the object. Strangely, the objects are being reflected at 45 degrees from the far horizon line and suddenly, from a virtual horizontal line, they start reflecting vertically as if the objects were totally vertical. And that happens at a precise vertical height on the water surface. This is exactly where the problem happens. For years, I have never seen any issues with reflections. If you have a scene with a city skyline in the horizon, you are less likely to see that kind of artifacts. In the present case, we have the equivalent of skyscrapers, but at 45 degrees. I also tried with Blender version 2.93 and the problem is the same. Before reporting this bug, I looked at the scene setup. To validate the nature of the problem, I decided to take into account the following factors. * The bump height and the distance are relatively low. Nothing exaggerated here to mess up the results. * The height of the camera is at 2 meters from the water surface, which is about the height of a human. Nothing exaggerated once again. I was not sure if that was a bug in Cycles or a limitation. I relied on the definition that has been given to me, “if it works as expected”, and clearly it is not working as expected. Therefore, I decided to report it. [ReflectionBug.blend](https://archive.blender.org/developer/F13159045/ReflectionBug.blend) ![Camera 1 - 2 meters high.jpg](https://archive.blender.org/developer/F13159047/Camera__1_-_2_meters_high.jpg) ![Camera 2 - 20 meters high.jpg](https://archive.blender.org/developer/F13159052/Camera__2_-_20_meters_high.jpg) ![Water_Large_SimpleReflectiony.jpg](https://archive.blender.org/developer/F13159054/Water_Large_SimpleReflectiony.jpg)

Sebastien Larocque commented

2022-06-14 02:41:06 +02:00

Added subscriber: @SebBlender

Germano Cavalcante commented

2022-06-14 21:15:01 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-06-14 21:15:01 +02:00

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

Germano Cavalcante commented

2022-06-14 21:15:01 +02:00

If fact is not the result that would be expected.
But as it is something as common as the bump, I avoid confirming it as a bug for now.
Needs Information from Developers

If fact is not the result that would be expected. But as it is something as common as the bump, I avoid confirming it as a bug for now. Needs Information from Developers

Philipp Oeser removed the

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Unexplained reflection logic (artifacts) on water shader with bump mapping #98869