Emission performance bug (cycles render) #108558

New Issue

TRIGON · 2023-06-02T22:17:52+02:00

TRIGON commented

2023-06-02 22:17:52 +02:00

System Information
Operating system: Win 11 Pro ( 10.0.22000 )
Graphics card: 3090

Blender Version
Broken:
3.5.1 steam version ( e1ccd9d4a1 ),
blender-3.5.0-stable+v35.1be25cfff18b-windows.amd64-release
blender-3.6.0-beta+v36.3788f70647a6-windows.amd64-release

Worked:
blender-3.3.6-stable+v33.948f8298b982-windows.amd64-release

When using the Emission node on a hi-poly object and the value of Emission Strength is greater than 0.5, then the render time increases dramatically (updating lights)
The bug is more noticeable when moving an object in mode Display Render preview.
The more polygons on the object, the more the bug manifests itself (100,000+)
If the Strength value is less than or equal to 0.5, the bug does not appear

Reproducing the error:
Option 1:
-Run emission_bug.blend
-Activate the Display Render preview mode
-In the Shader Editor, select one of the four material outputs
-Move the object plane in a circle
-We make sure that when the value of emission strength is higher than 0.5, the rendering time becomes much higher

Option 2:
-In the new scene create an object for 100 000+ polygons
-Assign a node material to the object
-Connect the Emission node to the material output
-Change the Strength value to 0.5 or less
-Activate the Display Render preview mode
-Move the object in a circle
-Make Strength higher than 0.5
-Move the object in a circle
-We make sure that when the value of emission strength is higher than 0.5, the rendering time becomes much higher

p.s: in Blender 3.6.0 the rendering speed is generally increased, but the bug still persists.
the bug was checked on 3 different systems, the behavior is the same everywhere

**System Information** Operating system: Win 11 Pro ( 10.0.22000 ) Graphics card: 3090 **Blender Version** Broken: 3.5.1 steam version ( e1ccd9d4a1d3 ), blender-3.5.0-stable+v35.1be25cfff18b-windows.amd64-release blender-3.6.0-beta+v36.3788f70647a6-windows.amd64-release Worked: blender-3.3.6-stable+v33.948f8298b982-windows.amd64-release **When using the Emission node on a hi-poly object and the value of Emission Strength is greater than 0.5, then the render time increases dramatically (updating lights) The bug is more noticeable when moving an object in mode Display Render preview. The more polygons on the object, the more the bug manifests itself (100,000+) If the Strength value is less than or equal to 0.5, the bug does not appear** **Reproducing the error:** **Option 1:** -Run **emission_bug.blend** -Activate the **Display Render preview** mode -In the **Shader Editor**, select one of the four **material outputs** -Move the object plane in a circle -We make sure that when the value of **emission strength** is higher than **0.5**, the rendering time becomes much higher **Option 2:** -In the new scene create an object for 100 000+ polygons -Assign a node material to the object -Connect the **Emission** node to the **material output** -Change the **Strength** value to **0.5** or less -Activate the **Display Render preview** mode -Move the object in a circle -Make **Strength** higher than **0.5** -Move the object in a circle -We make sure that when the value of **emission strength** is higher than **0.5**, the rendering time becomes much higher p.s: in Blender 3.6.0 the rendering speed is generally increased, but the bug still persists. the bug was checked on 3 different systems, the behavior is the same everywhere

emission_bug.blend

9.4 MiB

system-info.txt

24 KiB

TRIGON added the

labels 2023-06-02 22:17:53 +02:00

Jesse Yurkovich commented

2023-06-02 22:36:13 +02:00

This is mostly expected due to the use of the Light Tree feature : Render properties -> Sampling -> Lights -> Light Tree
https://docs.blender.org/manual/en/dev/render/cycles/render_settings/sampling.html#lights

Using the Light Tree often produces less noise during render but is more expensive to calculate for many emissive triangles.

Yes, performance was improved for 3.6 (the work to address #105550 for example). Future changes may improve this further but Light Tree calculations will always be more expensive than without.

@weizhen There's somewhat interesting behavior here with Emission strength of .4999 vs .5001. Do you think that merits any followup for this particular scene?

This is mostly expected due to the use of the Light Tree feature : `Render properties` -> `Sampling` -> `Lights` -> `Light Tree` https://docs.blender.org/manual/en/dev/render/cycles/render_settings/sampling.html#lights Using the Light Tree often produces less noise during render but is more expensive to calculate for many emissive triangles. Yes, performance was improved for 3.6 (the work to address #105550 for example). Future changes may improve this further but Light Tree calculations will always be more expensive than without. @weizhen There's somewhat interesting behavior here with Emission strength of .4999 vs .5001. Do you think that merits any followup for this particular scene?

Jesse Yurkovich added

Status

Needs Info from Developers

and removed

labels 2023-06-02 22:36:30 +02:00

Brecht Van Lommel commented

2023-06-02 22:47:54 +02:00

We have a heuristic where beyond a certain threshold it guesses the emission importance sampling is useful, this is just crossing that threshold. That is the expected behavior.

Emission sampling can be manually turned off in the material properties.

We have a heuristic where beyond a certain threshold it guesses the emission importance sampling is useful, this is just crossing that threshold. That is the expected behavior. Emission sampling can be manually turned off in the material properties.

Brecht Van Lommel closed this issue

2023-06-02 22:47:56 +02:00

Blender Bot added

Status

Archived

and removed

Status

Needs Info from Developers

labels 2023-06-02 22:47:58 +02:00

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