[Impeller] Fix nullopt access and simplify coverage computation in GetSubpassCoverage. by bdero · Pull Request #47347 · flutter/engine

bdero · 2023-10-26T19:16:45Z

Follow up for comments in #46130.

This case shouldn't actually be possible today, but we should be able to make this reasonably testable without goldens... added an issue to follow-up here: flutter/flutter#137356
This branch noise will also melt away with: flutter/flutter#137306

zanderso · 2023-10-26T19:22:37Z

impeller/entity/entity_pass.cc

          if (backdrop_coverage.has_value()) {
            if (unfiltered_coverage.has_value()) {
-              unfiltered_coverage = coverage->Union(*backdrop_coverage);
+              unfiltered_coverage = coverage.has_value()


I might be missing something, but I don't see how coverage.has_value() could ever be true here.

Also, this tests backdrop_coverage.has_value() after it already used the -> operator on it...

Is the bug here that the calculation should have been unfiltered_coverage->Union(*backdrop_coverage) all along?

Fixed, yeah this was supposed to union with unfiltered_coverage.

flar · 2023-10-26T20:20:38Z

impeller/entity/entity_pass.cc

            if (unfiltered_coverage.has_value()) {
-              unfiltered_coverage = coverage->Union(*backdrop_coverage);
+              unfiltered_coverage = coverage.has_value()
+                                        ? coverage->Union(*backdrop_coverage)


I have new functions in #47183 that perform nullopt aware Union and Intersection that might simplify this code.

flar · 2023-10-30T07:41:55Z

impeller/entity/entity_pass.cc

      // backdrop filter, then incorporate the backdrop filter in the
      // pre-filtered coverage of the subpass.
-      if (result.has_value() && subpass.backdrop_filter_proc_) {
+      if (accumulated_coverage.has_value() && subpass.backdrop_filter_proc_) {


Why is this based on accumulated_coverage? If there is a backdrop filter on one of the elements, then the subpass coverage should be automatically expanded to the coverage_limit, shouldn't it?

This is wrong when backdrop filters are destructive color filters, but don't detect this right now. This is already being tracked here: flutter/flutter#137090

Oh, I'm forgetting that BDF only operates on the current layer so it will depend on the accumulated coverage...

In the DiffContext partial repaint code BDF always accumulates the coverage_limit which is probably conservative for one that appears inside another layer (or one that appears with no previous "clear" command).

flar · 2023-10-30T07:43:04Z

impeller/entity/entity_pass.cc

          auto backdrop_coverage = backdrop_filter->GetCoverage({});
-          backdrop_coverage->origin += result->origin;
          if (backdrop_coverage.has_value()) {
+            backdrop_coverage->origin += accumulated_coverage->origin;


I'm not sure why this is done...? A BDF is independent of the prior content in the pass.

I think this is a bug and removed it... Let's see those goldens. The filter's coverage is computed above with an identity transform, but the placeholder rect given to the filter input should already contain the offset.

flar · 2023-10-30T07:44:10Z

impeller/entity/entity_pass.cc

            if (unfiltered_coverage.has_value()) {
-              unfiltered_coverage = coverage->Union(*backdrop_coverage);
+              unfiltered_coverage =
+                  unfiltered_coverage->Union(*backdrop_coverage);


This if/else can be replaced with unfiltered_coverage = Union(backdrop_coverage.value(), unfiltered_coverage)

flar · 2023-10-30T07:46:29Z

impeller/entity/entity_pass.cc

    }
-    result = result->Union(coverage.value());
+    accumulated_coverage =
+        accumulated_coverage->Union(element_coverage.value());


All of these lines (178-187) => accumulated_coverage = Union(accumulated_coverage, element_coverage)

flar · 2023-10-30T07:47:31Z

impeller/entity/entity_pass.cc

+      if (element_coverage.has_value() && coverage_limit.has_value() &&
          (!image_filter || image_filter->IsTranslationOnly())) {
-        coverage = coverage->Intersection(coverage_limit.value());
+        element_coverage =


My head is spinning a little here - why does image_filter disqualify this intersection?

We shouldn't need to guard against this anymore now that the coverage_limit incorporates image filters as we walk the subpasses (not that it was a correct fix to begin with). Removed it.

bdero · 2023-10-31T20:38:58Z

Whoops, didn't push my changes until now 😅

zanderso

lgtm if clang-tidy is happy and @flar's comments are addressed.

flar · 2023-10-31T22:34:23Z

impeller/entity/entity_pass.cc

-              unfiltered_coverage = backdrop_coverage;
-            }
+            unfiltered_coverage =
+                Union(backdrop_coverage.value(), unfiltered_coverage);


This can be further simplified to Union(unfiltered_coverage, backdrop_coverage)

(No need to test backdrop_coverage.has_value() around it as the Union overrides will do that for you.)

flar · 2023-10-31T22:40:24Z

impeller/entity/entity_pass.cc

-        current_clip_coverage->Intersection(
-            element_entity.GetContents()->GetCoverageHint().value()));
+        element_coverage_hint.value().Intersection(
+            current_clip_coverage.value()));


Can all of this be replaced by

element_entity.GetContents()->SetCoverageHint(Intersection(element_coverage_hint, current_clip_coverage)?

Sure can. Done.

bdero · 2023-10-31T23:29:46Z

Appreciate you taking a look for spots we can simplify with the new utils. I think it removes quite a bit of cognitive overhead while reading through this part of the codebase.

flar

Looks good. We should look at using GetSourceCoverage in there at some point.

flar · 2023-10-31T23:32:27Z

impeller/entity/entity_pass.cc

        if (!filter || filter->IsTranslationOnly()) {
-          coverage = coverage->Intersection(coverage_limit.value());
+          element_coverage =
+              element_coverage->Intersection(coverage_limit.value());


This looks like a good place to use filter->GetSourceCoverage, maybe as a follow-on?

flutter-dashboard · 2023-11-01T00:07:15Z

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie or stuartmorgan on the #hackers channel in Chat (don't just cc them here, they won't see it! Use Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

…on in GetSubpassCoverage. (flutter/engine#47347)

flutter/engine@db06c2e...a0ac6b4 2023-11-01 bdero@google.com [Impeller] Include cstdint everywhere that uint32_t is used. (flutter/engine#47533) 2023-11-01 bdero@google.com [Impeller] Fix nullopt access and simplify coverage computation in GetSubpassCoverage. (flutter/engine#47347) 2023-11-01 bdero@google.com [Impeller] OpenGLES: Ensure frag/vert textures are bound with unique texture units. (flutter/engine#47218) 2023-11-01 skia-flutter-autoroll@skia.org Roll Fuchsia Linux SDK from LCfhx_lTRJI51G0zc... to _TyF0etsONe5aqCbM... (flutter/engine#47532) 2023-11-01 jonahwilliams@google.com [Impeller] stencil buffer record/replay instead of MSAA storage. (flutter/engine#47397) 2023-11-01 chris@bracken.jp [macOS] Delete FlutterCompositor tests (flutter/engine#47527) 2023-10-31 bdero@google.com [Impeller] Place Rect statics under the Rect template. (flutter/engine#47529) 2023-10-31 skia-flutter-autoroll@skia.org Roll Skia from aaa225e0cc6d to 34ef20100acc (1 revision) (flutter/engine#47530) Also rolling transitive DEPS: fuchsia/sdk/core/linux-amd64 from LCfhx_lTRJI5 to _TyF0etsONe5 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

bdero added the e: impeller label Oct 26, 2023

bdero requested a review from zanderso October 26, 2023 19:16

bdero self-assigned this Oct 26, 2023

zanderso reviewed Oct 26, 2023

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chinmaygarde mentioned this pull request Oct 26, 2023

[Impeller] Remove NOLINT on entity_pass.cc. #47316

Closed

flar reviewed Oct 26, 2023

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bdero force-pushed the bdero/nullopt-access branch 3 times, most recently from a3d1a82 to 86535a6 Compare October 29, 2023 07:00

bdero marked this pull request as ready for review October 29, 2023 07:03

bdero force-pushed the bdero/nullopt-access branch from 86535a6 to b290657 Compare October 29, 2023 22:11

flar suggested changes Oct 30, 2023

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bdero requested review from flar and zanderso October 31, 2023 19:26

bdero force-pushed the bdero/nullopt-access branch from b290657 to 0fccf6f Compare October 31, 2023 20:38

zanderso approved these changes Oct 31, 2023

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bdero force-pushed the bdero/nullopt-access branch from 0fccf6f to 8e6b898 Compare October 31, 2023 22:29

flar suggested changes Oct 31, 2023

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flar approved these changes Oct 31, 2023

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bdero added 2 commits October 31, 2023 17:06

[Impeller] Fix nullopt access in GetSubpassCoverage.

8554733

Address comments

9e6eab5

bdero changed the title ~~[Impeller] Fix nullopt access in GetSubpassCoverage.~~ [Impeller] Fix nullopt access and simplify coverage computation in GetSubpassCoverage. Nov 1, 2023

Simplify

c26fd1b

bdero force-pushed the bdero/nullopt-access branch from db240bf to c26fd1b Compare November 1, 2023 00:09

bdero merged commit 0c53706 into flutter:main Nov 1, 2023

engine-flutter-autoroll mentioned this pull request Nov 1, 2023

Roll Flutter Engine from db06c2e10459 to a0ac6b432cdf (8 revisions) flutter/flutter#137656

Merged

engine-flutter-autoroll added a commit to engine-flutter-autoroll/flutter that referenced this pull request Nov 1, 2023

0c53706 [Impeller] Fix nullopt access and simplify coverage computati…

5c1f583

…on in GetSubpassCoverage. (flutter/engine#47347)

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bdero commented Oct 26, 2023

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bdero Oct 31, 2023 •

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