Bug 237533

Summary:

iOS/iPad 15.3.1 slow drawElements with TRIANGLE_FAN mode

Product:

WebKit

Reporter:

Marcin <msokalski>

Component:

WebGL

Assignee:

Nobody <webkit-unassigned>

Status:

NEW

Severity:

Normal

CC:

dino, gman, johncunningham, kbr, kkinnunen, kpiddington, webkit-bug-importer

Priority:

Keywords:

InRadar

Version:

Safari 15

Hardware:

iPhone / iPad

OS:

iOS 15

Bug Depends on:

231180

Bug Blocks:

Attachments:

Description	Flags
gl.drawElements primitive restart / regular performance comparison	none
Added TRIANGLE_STRIP to the test	none
drawElements with mode = TRIANGLE_STRIP vs TRIANGLE_FAN vs TRIANGLES	none

Marcin

Reported 2022-03-07 08:23:10 PST

On iOS/iPad 15.3.1 gl.drawElements with gl.UNSIGNED_INT index buffer containing ~0 to restart gl.TRIANGLE_FAN geometry is incredibly slow. I haven't checked UNSIGNED_SHORT, UNSIGNED_BYTE types but switching to gl.TRIANGLES without primitive restarts works OK.

Attachments
gl.drawElements primitive restart / regular performance comparison (9.31 KB, text/html) 2022-03-08 05:01 PST, Marcin	no flags	Details
Added TRIANGLE_STRIP to the test (10.62 KB, text/html) 2022-03-08 05:51 PST, Marcin	no flags	Details
drawElements with mode = TRIANGLE_STRIP vs TRIANGLE_FAN vs TRIANGLES (9.15 KB, text/html) 2022-03-08 06:57 PST, Marcin	no flags	Details
View All Add attachment proposed patch, testcase, etc.

Kimmo Kinnunen

Comment 1 2022-03-07 11:15:53 PST

Thanks for the report. If you have a self contained test case, feel free to attach / link that, it always helps. (Primitive restart is "emulated" when running on Metal, and the implementation might not be as tuned as the older OpenGL-based implementation)

Marcin

Comment 2 2022-03-08 05:01:55 PST

Created attachment 454105 [details] gl.drawElements primitive restart / regular performance comparison

Marcin

Comment 3 2022-03-08 05:03:22 PST

You're welcome Kimmo. Thank you for letting me know it has to be emulated in metal. Please find performance comparison attached. Note, adding burst loop was necessary to show the difference. If I'd call gl.drawElements simply once per frame, there was no performance difference between TRIANGLES w/o restarts and TRIANGLE_FAN with restarts.

Marcin

Comment 4 2022-03-08 05:50:08 PST

After playing a while with the test case, I've noticed TRIANGLE_STRIP with primitive restart IS NOT affected.

Marcin

Comment 5 2022-03-08 05:51:27 PST

Created attachment 454113 [details] Added TRIANGLE_STRIP to the test

Marcin

Comment 6 2022-03-08 06:55:52 PST

Finally it appears the problem has nothing to do with primitive restarts. I've narrowed regression to drawElements with mode=TRIANGLE_FAN. drawArrays is NOT AFFECTED.

Marcin

Comment 7 2022-03-08 06:57:29 PST

Created attachment 454117 [details] drawElements with mode = TRIANGLE_STRIP vs TRIANGLE_FAN vs TRIANGLES

Radar WebKit Bug Importer

Comment 8 2022-03-10 10:17:26 PST

<rdar://problem/90106467>

Marcin

Comment 9 2022-04-11 06:35:49 PDT

Still reproducible on iOS/iPad 15.4.1

Marcin

Comment 10 2022-10-03 02:26:19 PDT

Still reproducible on iOS/iPad 15.7

Marcin

Comment 11 2022-10-07 08:26:18 PDT

Disabling WebGL via Metal solves the problem

Kimmo Kinnunen

Comment 12 2022-10-11 01:27:35 PDT

Thanks for continuing to investigate. I filed upstream ANGLE bug at: https://bugs.chromium.org/p/angleproject/issues/detail?id=7748 Metal does not support TRIANGLE_FAN drawing mode natively. ANGLE emulates it. The GPU implementation of the emulation is turned off when primitive restart is supported. For WebGL2 primitive restart is enabled. To get an idea of the perf difference after the emulation is fixed to work with primitive restart, you can try to change the test case: - use WebGL1 or - change to drawArrays, where the emulation generates the emulated buffer once per draw after modification.

Marcin

Comment 13 2022-10-11 03:58:28 PDT

Thanks Kimmo, Please note, performance issue happens also in drawArrays with triangle fan mode. (last attachment)

Marcin

Comment 14 2022-10-11 04:01:13 PDT

Oops, I messed drawArrays / drawElements test cases, I'll re-check what's going on ...

Marcin

Comment 15 2022-10-11 05:14:50 PDT

So, you are right, that's only drawElements issue, I'm sorry for making unnecessary comments :(

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