Ensure that textLayers can be rendered in parallel, without interfering with each other #18731
Conversation
Snuffleupagus
force-pushed
the
TextLayer-ensureCtxFont
branch
from
7a4cc9a
to
4504e63
Compare
Snuffleupagus
force-pushed
the
TextLayer-ensureCtxFont
branch
5 times, most recently
from
6035174
to
92cc697
Compare
From: Bot.io (Linux m4)ReceivedCommand cmd_test from @Snuffleupagus received. Current queue size: 0 Live output at: http://54.241.84.105:8877/99e4628a7c07bd7/output.txt |
From: Bot.io (Windows)ReceivedCommand cmd_test from @Snuffleupagus received. Current queue size: 0 Live output at: http://54.193.163.58:8877/7a74393f4fc2ab2/output.txt |
From: Bot.io (Linux m4)FailedFull output at http://54.241.84.105:8877/99e4628a7c07bd7/output.txt Total script time: 31.25 mins
Image differences available at: http://54.241.84.105:8877/99e4628a7c07bd7/reftest-analyzer.html#web=eq.log |
From: Bot.io (Windows)FailedFull output at http://54.193.163.58:8877/7a74393f4fc2ab2/output.txt Total script time: 46.50 mins
Image differences available at: http://54.193.163.58:8877/7a74393f4fc2ab2/reftest-analyzer.html#web=eq.log |
…ng with each other Note that the textContent is returned in "chunks" from the API, through the use of `ReadableStream`s, and on the main-thread we're (normally) using just one temporary canvas in order to measure the size of the textLayer `span`s; see the [`#layout`](https://github.com/mozilla/pdf.js/blob/5b4c2fe1a845169ac2b4f8f6335337c434077637/src/display/text_layer.js#L396-L428) method. *Order of events, for parallel textLayer rendering:* 1. Call [`render`](https://github.com/mozilla/pdf.js/blob/5b4c2fe1a845169ac2b4f8f6335337c434077637/src/display/text_layer.js#L155-L177) of the textLayer for page A. 2. Immediately call `render` of the textLayer for page B. 3. The first text-chunk for pageA arrives, and it's parsed/layout which means updating the cached [fontSize/fontFamily](https://github.com/mozilla/pdf.js/blob/5b4c2fe1a845169ac2b4f8f6335337c434077637/src/display/text_layer.js#L409-L413) for the textLayer of page A. 4. The first text-chunk for pageB arrives, which means updating the cached fontSize/fontFamily *for the textLayer of page B* since this data is unique to each `TextLayer`-instance. 5. The second text-chunk for pageA arrives, and we don't update the canvas-font since the cached fontSize/fontFamily still apply from step 3 above. Where this potentially breaks down is between the last steps, since we're using just one temporary canvas for all measurements but have *individual* fontSize/fontFamily caches for each textLayer. Hence it's possible that the canvas-font has actually changed, despite the cached values suggesting otherwise, and to address this we instead cache the fontSize/fontFamily globally through a new (static) helper method. *Note:* Includes a basic unit-test, using dummy text-content, which fails on `master` and passes with this patch. Finally, pun intended, ensure that temporary textLayer-data is cleared *before* the `render`-promise resolves to avoid any intermittent problems in the unit-tests.
Snuffleupagus
force-pushed
the
TextLayer-ensureCtxFont
branch
from
92cc697
to
5b3d3c7
Compare
|
/botio test |
From: Bot.io (Linux m4)ReceivedCommand cmd_test from @Snuffleupagus received. Current queue size: 0 Live output at: http://54.241.84.105:8877/b81d004fdda1f43/output.txt |
From: Bot.io (Windows)ReceivedCommand cmd_test from @Snuffleupagus received. Current queue size: 0 Live output at: http://54.193.163.58:8877/97a53bd4c55d06e/output.txt |
From: Bot.io (Linux m4)FailedFull output at http://54.241.84.105:8877/b81d004fdda1f43/output.txt Total script time: 30.98 mins
Image differences available at: http://54.241.84.105:8877/b81d004fdda1f43/reftest-analyzer.html#web=eq.log |
From: Bot.io (Windows)FailedFull output at http://54.193.163.58:8877/97a53bd4c55d06e/output.txt Total script time: 47.37 mins
Image differences available at: http://54.193.163.58:8877/97a53bd4c55d06e/reftest-analyzer.html#web=eq.log |
Note that the textContent is returned in "chunks" from the API, through the use of
ReadableStreams, and on the main-thread we're (normally) using just one temporary canvas in order to measure the size of the textLayerspans; see the#layoutmethod.Order of events, for parallel textLayer rendering:
renderof the textLayer for page A.renderof the textLayer for page B.TextLayer-instance.Where this potentially breaks down is between the last steps, since we're using just one temporary canvas for all measurements but have individual fontSize/fontFamily caches for each textLayer.
Hence it's possible that the canvas-font has actually changed, despite the cached values suggesting otherwise, and to address this we instead cache the fontSize/fontFamily globally through a new (static) helper method.
Note: Includes a basic unit-test, using dummy text-content, which fails on
masterand passes with this patch.Finally, pun intended, ensure that temporary textLayer-data is cleared before the
render-promise resolves to avoid any intermittent problems in the unit-tests.Closes #18709