[Impeller] add support for specialization constants. #47432

jonahwilliams · 2023-10-29T02:35:56Z

Adds support for Specialization constants to Impeller for our usage in the engine. A motivating example has been added in the impeller markdown docs.

Fixes flutter/flutter#136210
Fixes flutter/flutter#119357

impeller/entity/shaders/blending/blend_dispatch.glsl

impeller/renderer/backend/gles/pipeline_library_gles.cc

impeller/renderer/pipeline_descriptor.h

…/engine into add_specialization_support

jonahwilliams · 2023-10-30T21:37:58Z

Some pending work, I need to verify + test that Variants are working correctly with the spec constants.

jonahwilliams · 2023-10-30T21:52:54Z

Test added for that.

matanlurey

Only reviewed the docs, thanks!

matanlurey · 2023-10-30T21:45:10Z

impeller/docs/specialization_constants.md

@@ -0,0 +1,90 @@
+# Specialization Constants
+


It would be nice to start with 1-2 sentences describing what a specialization constant is. This is my first time hearing the phrase, and I tried a Google search, and as you can see it's not clear where to start.

Maybe (assuming I understand now):

"""
A specialization constant, or a shader constant that can be set at runtime, allowing for more efficient code generation and flexibility.
"""

matanlurey · 2023-10-30T21:48:04Z

impeller/docs/specialization_constants.md

+  * Improving performance, by removing branching and conditional code.
+  * Code organization/size, by removing the number of shader source files required.
+
+These goals are interrrelated, we can always reduce the number of shaders by creating


Suggested change

These goals are interrrelated, we can always reduce the number of shaders by creating

These goals are interrelated, we can always reduce the number of shaders by creating

matanlurey · 2023-10-30T21:54:40Z

impeller/docs/specialization_constants.md

+
+## Implementation
+
+Currently the only constant values that are support are 32bit ints. This should be sufficient for now as we


I would re-write this paragraph (tried to do it via GH suggestions) to be more opinionated. Something like:

32-bit integers are supported as constant values and should represent: - `true`/`false` (example) - select-style constants: (example)

AVOID adding constant color values or anything more complex.

bdero · 2023-10-31T19:50:22Z

Taking a look 👀

bdero

Warning

This patch is pretty cool.

ⓘ Note
Nits and minor questions.

bdero · 2023-10-31T18:29:01Z

impeller/entity/shaders/blending/blend_select.glsl

+// kSaturation,
+// kColor,
+// kLuminosity,
+// Note, this isn't a switch as GLSL 1.0 does not support them.


Suggested change

// Note, this isn't a switch as GLSL 1.0 does not support them.

// Note, this isn't a switch as GLSL ES 1.0 does not support them.

bdero · 2023-10-31T19:41:21Z

impeller/renderer/backend/gles/proc_table_gles.cc

+  auto shader_source = std::string{
+      reinterpret_cast<const char*>(mapping.GetMapping()), mapping.GetSize()};
+
+  auto index = shader_source.find('\n');


Could you add a comment that this is here to skip over the #version line, which impellerc is expected to always emit as the first line of a GLES shader? (Unless that's not what this is for)

bdero · 2023-10-31T19:56:40Z

impeller/renderer/backend/vulkan/pipeline_library_vk.cc

+  const auto& constants = desc.GetSpecializationConstants();
+
+  std::vector<std::vector<vk::SpecializationMapEntry>> map_entries(
+      desc.GetStageEntrypoints().size());


Do we need this outer vector? It looks like this could be a std::vector<vk::SpecializationMapEntry> in the entrypoint loop.

The VkSpecializationInfo holds onto a ptr to the VkSpecializationMapEntry, so we need to keep all of this alive/in scope until we actually create the pipeline.

bdero · 2023-10-31T20:24:22Z

impeller/docs/specialization_constants.md

+*AVOID* adding specialization constants for color values or anything more complex.
+
+Specialization constants are provided to the CreateDefault argument in content_context.cc and aren't a
+part of variants. This is intentional: specialization constants shouldn't be used to create (potentially unlimited) runtime variants of a shader.


This along with restriction to 32bit ints both seem reasonable to me... Best not to hide our shader volume lest we accidentally land combinatorial explosions.

jonahwilliams · 2023-11-01T00:14:35Z

This PR and #47397 both have the chance of interacting with the advanced blend benchmark. In the interest of sanity I'm going to land that one first and sit on this one for another day or so.

…er/engine#47432)

…137785) flutter/engine@2ec0f74...b11e318 2023-11-02 skia-flutter-autoroll@skia.org Roll Skia from 70634da5c783 to 2b3472da9888 (5 revisions) (flutter/engine#47608) 2023-11-02 jonahwilliams@google.com [Impeller] add support for specialization constants. (flutter/engine#47432) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-engine-flutter-autoroll Please CC rmistry@google.com,zra@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

…#47432)" This reverts commit f899cc7.

#47651) This reverts commit f899cc7. This is the same revert as #47650, but for the 3.17 release branch.

Reland of #47432 Also includes: * #47617 * #47637 Fixes the performance on iOS by removing blocking on compilation of shaders. From local testing this has identical before/after numbers. Additional, ensures that we don't unecessarily specialize vertex shaders and notes this restriction in the documentation. ---- Adds support for Specialization constants to Impeller for our usage in the engine. A motivating example has been added in the impeller markdown docs. Fixes flutter/flutter#136210 Fixes flutter/flutter#119357

…47762) Reverts #47678 Initiated by: jonahwilliams This change reverts the following previous change: Original Description: Reland of #47432 Also includes: * #47617 * #47637 Fixes the performance on iOS by removing blocking on compilation of shaders. From local testing this has identical before/after numbers. Additional, ensures that we don't unecessarily specialize vertex shaders and notes this restriction in the documentation. ---- Adds support for Specialization constants to Impeller for our usage in the engine. A motivating example has been added in the impeller markdown docs. Fixes flutter/flutter#136210 Fixes flutter/flutter#119357

Reland of #47432 Also includes: #47617 #47637 Fixes the performance on iOS by removing blocking on compilation of shaders. From local testing this has identical before/after numbers. Additional, ensures that we don't unecessarily specialize vertex shaders and notes this restriction in the documentation. Adds support for Specialization constants to Impeller for our usage in the engine. A motivating example has been added in the impeller markdown docs. Fixes flutter/flutter#136210 Fixes flutter/flutter#119357 Investigating: flutter/flutter#138028

[Impeller] add support for specialization constants.

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jonahwilliams added 3 commits October 28, 2023 20:18

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Merge branch 'main' into add_specialization_support

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Merge branch 'add_specialization_support' of github.com:jonahwilliams…

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…/engine into add_specialization_support

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GLES fixes

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jonahwilliams marked this pull request as ready for review October 30, 2023 21:35

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jonahwilliams added 2 commits October 30, 2023 15:52

update markdown doc.

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jonahwilliams added 2 commits November 1, 2023 13:21

Merge branch 'main' into add_specialization_support

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Merge branch 'main' into add_specialization_support

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Merge branch 'main' into add_specialization_support

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auto-submit bot merged commit f899cc7 into flutter:main Nov 2, 2023
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engine-flutter-autoroll mentioned this pull request Nov 2, 2023

Roll Flutter Engine from 2ec0f74a1e8a to b11e318b3690 (2 revisions) flutter/flutter#137785

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f899cc7b4 [Impeller] add support for specialization constants. (flutt…

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zanderso mentioned this pull request Nov 3, 2023

specialization constants crashing Moto G4 driver flutter/flutter#137816

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…#47432)" This reverts commit f899cc7.

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…#47432)" This reverts commit f899cc7.

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#47651) This reverts commit f899cc7. This is the same revert as #47650, but for the 3.17 release branch.

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[Impeller] Add support for specialization constants redux. #47678

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Reverts "[Impeller] Add support for specialization constants redux." #47762

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[Impeller] Add support for specialization constants (III). #47765

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[Impeller] add support for specialization constants. #47432

[Impeller] add support for specialization constants. #47432

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jonahwilliams commented Nov 1, 2023

	These goals are interrrelated, we can always reduce the number of shaders by creating
	These goals are interrelated, we can always reduce the number of shaders by creating


		## Implementation

		Currently the only constant values that are support are 32bit ints. This should be sufficient for now as we

	// Note, this isn't a switch as GLSL 1.0 does not support them.
	// Note, this isn't a switch as GLSL ES 1.0 does not support them.

[Impeller] add support for specialization constants. #47432

[Impeller] add support for specialization constants. #47432

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