Offload canvas drawing operations to a worker by Aditi-1400 · Pull Request #20729 · mozilla/pdf.js

Aditi-1400 · 2026-02-24T09:55:54Z

This is a follow-up of: #20053

This change works on top of #20016 to move CanvasGraphics operations to a new/different worker thread, thus offloading the heavy page renders and freeing up the main thread.

Note: The TODO(Aditi) comments need to be resolved to mark this pull request as non-draft

codecov-commenter · 2026-02-24T09:58:14Z

Codecov Report

❌ Patch coverage is 50.40584% with 611 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.40%. Comparing base (d38cddf) to head (ba0fa2c).

Files with missing lines	Patch %	Lines
src/display/api.js	42.58%	395 Missing ⚠️
src/core/evaluator.js	54.16%	121 Missing ⚠️
src/display/object_handler.js	80.64%	30 Missing ⚠️
src/core/worker.js	25.71%	26 Missing ⚠️
src/display/canvas.js	42.22%	26 Missing ⚠️
src/display/optional_content_config.js	25.00%	6 Missing ⚠️
src/display/canvas_factory.js	61.53%	5 Missing ⚠️
src/display/worker_options.js	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20729      +/-   ##
==========================================
- Coverage   62.57%   62.40%   -0.17%     
==========================================
  Files         173      174       +1     
  Lines      121255   122252     +997     
==========================================
+ Hits        75876    76297     +421     
- Misses      45379    45955     +576

Flag	Coverage Δ
fonttest	`7.66% <ø> (ø)`
unittestcli	`62.38% <50.40%> (-0.17%)`	⬇️

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nicolo-ribaudo · 2026-02-24T11:15:42Z

/botio test

moz-tools-bot · 2026-02-24T11:15:45Z

From: Bot.io (Windows)

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Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.193.163.58:8877/e0227fb9789b076/output.txt

moz-tools-bot · 2026-02-24T11:15:45Z

From: Bot.io (Linux m4)

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Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.241.84.105:8877/b6e4acc21cb49a8/output.txt

moz-tools-bot · 2026-02-24T12:02:40Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.241.84.105:8877/b6e4acc21cb49a8/output.txt

Total script time: 46.91 mins

Unit tests: FAILED
Integration Tests: FAILED
Regression tests: FAILED

  different ref/snapshot: 14

Image differences available at: http://54.241.84.105:8877/b6e4acc21cb49a8/reftest-analyzer.html#web=eq.log

moz-tools-bot · 2026-02-24T12:46:14Z

From: Bot.io (Windows)

Failed

Full output at http://54.193.163.58:8877/e0227fb9789b076/output.txt

Total script time: 90.47 mins

Unit tests: FAILED
Integration Tests: FAILED
Regression tests: FAILED

  different ref/snapshot: 13

Image differences available at: http://54.193.163.58:8877/e0227fb9789b076/reftest-analyzer.html#web=eq.log

nicolo-ribaudo · 2026-03-09T13:47:32Z

I was looking through the reftest failures, it seems like the only real ones (the others are minor pixel differences due to the different rendering pipeline, but not visible to humans) are:

issue8092
issue16127 (for the gradients inside the font)
ShowText-ShadingPattern (probably same problem as issue8092)
issue1133 (page 4, in the huawei logo)
issue19022

Aditi-1400 · 2026-03-09T17:41:37Z

I was looking through the reftest failures, it seems like the only real ones (the others are minor pixel differences due to the different rendering pipeline, but not visible to humans) are:

issue8092

issue16127 (for the gradients inside the font)

ShowText-ShadingPattern (probably same problem as issue8092)

issue1133 (page 4, in the huawei logo)

issue19022

There's also gradient difference in 17069, also there are differences in 19022, same as issue8092

nicolo-ribaudo · 2026-03-09T17:50:20Z

/botio test

moz-tools-bot · 2026-03-09T17:50:23Z

From: Bot.io (Windows)

Received

Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.193.163.58:8877/832219967f9b55d/output.txt

moz-tools-bot · 2026-03-09T17:50:25Z

From: Bot.io (Linux m4)

Received

Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.241.84.105:8877/659eb95d2835e52/output.txt

moz-tools-bot · 2026-03-09T18:37:08Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.241.84.105:8877/659eb95d2835e52/output.txt

Total script time: 46.69 mins

Unit tests: Passed
Integration Tests: FAILED
Regression tests: FAILED

  different ref/snapshot: 12

Image differences available at: http://54.241.84.105:8877/659eb95d2835e52/reftest-analyzer.html#web=eq.log

moz-tools-bot · 2026-03-09T19:08:28Z

From: Bot.io (Windows)

Failed

Full output at http://54.193.163.58:8877/832219967f9b55d/output.txt

Total script time: 78.06 mins

Unit tests: Passed
Integration Tests: Passed
Regression tests: FAILED

  different ref/snapshot: 12

Image differences available at: http://54.193.163.58:8877/832219967f9b55d/reftest-analyzer.html#web=eq.log

…nCanvas

nicolo-ribaudo · 2026-03-16T15:47:57Z

/botio test

moz-tools-bot · 2026-03-16T15:48:01Z

From: Bot.io (Windows)

Received

Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.193.163.58:8877/528a274cb665c1e/output.txt

moz-tools-bot · 2026-03-16T15:48:02Z

From: Bot.io (Linux m4)

Received

Command cmd_test from @nicolo-ribaudo received. Current queue size: 0

Live output at: http://54.241.84.105:8877/67316c0b179c2dc/output.txt

moz-tools-bot · 2026-03-16T16:34:32Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.241.84.105:8877/67316c0b179c2dc/output.txt

Total script time: 46.49 mins

Unit tests: Passed
Integration Tests: FAILED
Regression tests: FAILED

  different ref/snapshot: 1

Image differences available at: http://54.241.84.105:8877/67316c0b179c2dc/reftest-analyzer.html#web=eq.log

moz-tools-bot · 2026-03-16T17:03:27Z

From: Bot.io (Windows)

Failed

Full output at http://54.193.163.58:8877/528a274cb665c1e/output.txt

Total script time: 75.41 mins

Unit tests: Passed
Integration Tests: FAILED
Regression tests: FAILED

  different ref/snapshot: 1

Image differences available at: http://54.193.163.58:8877/528a274cb665c1e/reftest-analyzer.html#web=eq.log

timvandermeij added core viewer labels Feb 24, 2026

Aditi-1400 force-pushed the worker-drawing branch from 03ad6c3 to 1afc3d4 Compare March 4, 2026 09:49

Aditi-1400 force-pushed the worker-drawing branch 4 times, most recently from 1d6de6c to 43a73d7 Compare March 9, 2026 17:10

Aditi-1400 force-pushed the worker-drawing branch from 5fb68aa to 134955c Compare March 16, 2026 13:53

Aditi-1400 added 9 commits March 16, 2026 19:31

Add object_handler class

c49a2cc

Setup renderer worker

be054fa

Transfer canvas, optionalContentConfig, factories to renderer worker

2c6b986

Forward objects to the worker, execute operator list in the worker

915a4e5

Fix filters, annotation canvases

8f9f8de

fixup! Fix filters, annotation canvases

6ccd790

fixup! Fix filters, annotation canvases

48b6b71

fixup! fixup! Fix filters, annotation canvases

7f663e5

fixup! Fix filters, annotation canvases

ce80f7f

Aditi-1400 added 7 commits March 16, 2026 19:34

Fix unittestcli failure

d00ca20

Modify 'extractCanvases' and 'isCanvasMonochrome' to support OffScree…

c92f057

…nCanvas

Fix scroll bug in renderer worker

9679870

Add header to object_handler.js

b81acbc

Use main-thread rendering for thumbnail canvases

af744f8

Traverse font resources to check for filters

21a76ac

Rebase fixup

ba0fa2c

Aditi-1400 force-pushed the worker-drawing branch from 134955c to ba0fa2c Compare March 16, 2026 15:29

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