Cycles: Use Blender headers to access geometry data, avoid copy #112306

Hans Goudey · 2023-09-12T22:54:30+02:00

Hans Goudey commented

2023-09-12 22:54:30 +02:00

Since 34b4487844, attributes are always made mutable when
accessed from the RNA API. This can result in unnecessary copies, which
increases memory usage and reduces performance.

Cycles is the only user of the C++ RNA API, which we'd like to remove
in the future since it doesn't really make sense in the big picture. Hydra is
now a better alternative for external render engines.

To start that change and fix the unnecessary copies, this commit
moves to use Blender headers directly for accessing attribute and other
geometry data. This also removes the few places that still had
overhead from the RNA API after the changes (0) in 3.6. In a simple
test with a large grid, I observed a 1.76x performance improvement,
from 1.04 to 0.59 seconds to extract the mesh data to Cycles.

Pull Request: #112306

Since 34b44878449d67a56fd2, attributes are always made mutable when accessed from the RNA API. This can result in unnecessary copies, which increases memory usage and reduces performance. Cycles is the only user of the C++ RNA API, which we'd like to remove in the future since it doesn't really make sense in the big picture. Hydra is now a better alternative for external render engines. To start that change and fix the unnecessary copies, this commit moves to use Blender headers directly for accessing attribute and other geometry data. This also removes the few places that still had overhead from the RNA API after the changes ([0]) in 3.6. In a simple test with a large grid, I observed a 1.76x performance improvement, from 1.04 to 0.59 seconds to extract the mesh data to Cycles. [0]: https://wiki.blender.org/wiki/Reference/Release_Notes/3.6/Cycles#Performance Pull Request: https://projects.blender.org/blender/blender/pulls/112306

🎉 1 🚀 6

Hans Goudey added 2 commits 2023-09-12 22:54:43 +02:00

4b3fdeeb47 Cycles: Use Blender headers to access geometry

buildbot/vexp-code-patch-coordinator Build done. Details

a34765161e Merge branch 'main' into cycles-blender-geometry-no-copy

Hans Goudey requested review from Brecht Van Lommel 2023-09-12 22:54:57 +02:00

Hans Goudey added this to the Render & Cycles project 2023-09-12 22:55:13 +02:00

Hans Goudey commented

2023-09-12 22:55:19 +02:00

@blender-bot build

Hans Goudey commented

2023-09-13 02:16:33 +02:00

I have no clue about the freestyle test failures yet. I'll have to figure out how that could be related to these changes

![image](/attachments/627ac20a-7fbc-4de5-9cc2-80339c7f889d) I have no clue about the freestyle test failures yet. I'll have to figure out how that could be related to these changes

image.png

152 KiB

Hans Goudey added 2 commits 2023-09-13 02:16:36 +02:00

39ce411988 Merge branch 'main' into cycles-blender-geometry-no-copy

0fc4ff058b Remove commented code

Sergey Sharybin reviewed 2023-09-13 16:23:36 +02:00

intern/cycles/blender/attribute_convert.h

						
				@ -0,0 +2,4 @@

				 *

				 * SPDX-License-Identifier: Apache-2.0 */

				#ifndef __BLENDER_ATTRIBUTE_CONVERT_H__

Sergey Sharybin commented

2023-09-13 16:23:31 +02:00

In the new code we use #pragma once.
Perhaps we should just go ahead and convert the header guards to uniform case, similar to what we did in Blender.

In the new code we use `#pragma once`. Perhaps we should just go ahead and convert the header guards to uniform case, similar to what we did in Blender.

intern/cycles/blender/mesh.cpp Outdated

						
				@ -399,0 +331,4 @@

				              src[tri.tri[0]][0], src[tri.tri[0]][1], src[tri.tri[0]][2], src[tri.tri[0]][3]);

				          data[i * 3 + 1] = make_uchar4(

				              src[tri.tri[1]][0], src[tri.tri[1]][1], src[tri.tri[1]][2], src[tri.tri[1]][3]);

				          data[i * 3 + 1] = make_uchar4(