Fix #109583: Avoid non-threadsafe writing to custom normals data #110478

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Hans Goudey merged 7 commits from HooglyBoogly/blender:fix-no-custom-normals-write into main 2023-07-26 17:04:19 +02:00
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Currently, while calculating face corner normals, Blender retrieves
custom normal data with write access. When the the custom normals in a
single smooth corner fan don't match, they are reset to the average
value.

This behavior is very old, but it comes from when Blender didn't have a
strong idea of const correctness. Indeed, modifying custom normal data
while calculating normals isn't threadsafe, which is important because
normals are calculated for viewport drawing, for example. And in the
future, properly caching face corner normals (see #93551) will require
the ability to calculate normals on a properly const mesh.

The fix is to still use the average of custom normals in a fan, but
not write that back to the custom data array. In my testing the results
are the same. Setting custom normals still fills the same value for all
corners in a fan.

Currently, while calculating face corner normals, Blender retrieves custom normal data with write access. When the the custom normals in a single smooth corner fan don't match, they are reset to the average value. This behavior is very old, but it comes from when Blender didn't have a strong idea of const correctness. Indeed, modifying custom normal data while calculating normals isn't threadsafe, which is important because normals are calculated for viewport drawing, for example. And in the future, properly caching face corner normals (see #93551) will require the ability to calculate normals on a properly const mesh. The fix is to still use the average of custom normals in a fan, but not write that back to the custom data array. In my testing the results are the same. Setting custom normals still fills the same value for all corners in a fan.
Hans Goudey added 1 commit 2023-07-25 22:06:24 +02:00
Hans Goudey changed title from Fix: Avoid non-threadsafe writing to custom normals data to Fix #109583: Avoid non-threadsafe writing to custom normals data 2023-07-25 22:12:48 +02:00
Hans Goudey added 3 commits 2023-07-26 06:15:32 +02:00
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@blender-bot build

@blender-bot build
Hans Goudey added 1 commit 2023-07-26 14:24:04 +02:00
Jacques Lucke approved these changes 2023-07-26 15:47:14 +02:00
@ -948,9 +948,6 @@ static void split_loop_nor_fan_do(LoopSplitTaskDataCommon *common_data,
/* We validate clnors data on the fly - cheapest way to do! */
Member

Probably need to update the comment.

Probably need to update the comment.
HooglyBoogly marked this conversation as resolved
Hans Goudey added 2 commits 2023-07-26 17:03:20 +02:00
Hans Goudey merged commit 580833165c into main 2023-07-26 17:04:19 +02:00
Hans Goudey deleted branch fix-no-custom-normals-write 2023-07-26 17:04:23 +02:00
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Reference: blender/blender#110478
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