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[Impeller] Avoid sharing scale information between TextFrame rendering calls#182539

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flar:impeller-text-frame-no-render-data-sharing
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[Impeller] Avoid sharing scale information between TextFrame rendering calls#182539
flar wants to merge 3 commits into
flutter:masterfrom
flar:impeller-text-frame-no-render-data-sharing

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@flar

@flar flar commented Feb 18, 2026

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Impeller has been storing rendering data specific to a single invocation of a text operation in the TextFrame object itself. Unfortunately, the TextFrame lives (most commonly, especially in a Flutter app) in the DisplayList which should be an immutable data store. Even more importantly, DisplayLists can be shared and appear multiple times in different graphics contexts within a single frame. This potentially means that Impeller might store "this TextFrame is rendering at a scale of 2x" and "this TextFrame is rendering at a scale of 50x" into the same TextFrame object in the same scene and then try to render that TextFrame with the most recently stored information for both instances. This issue was discovered during a code read of the way that glyph caches are managed in Impeller as mentioned in the targeted issue:

Fixes: #177424

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@github-actions github-actions Bot added a: text input Entering text in a text field or keyboard related problems engine flutter/engine related. See also e: labels. e: impeller Impeller rendering backend issues and features requests labels Feb 18, 2026
@flar flar requested a review from eyebrowsoffire February 18, 2026 11:40
@flar

flar commented Feb 18, 2026

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I'm seeing some flashing text running Wondrous that I need to investigate...

@flar flar mentioned this pull request Feb 19, 2026
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flar commented Feb 19, 2026

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I tracked the problem down to a mismatch of the drawText operations encountered during the FirstPass and the eventual Render pass. See #182639 for a full writeup.

It looks like the cull rects we use when traversing the Frame's DL during the FirstPass can sometimes be larger than the cull rects we use during the rendering pass.

Log of cull rects encountered during a Wondrous frame that skipped a drawText call 
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1347)] Render2Target first pass cull rect: ((0, 0) => (1080, 2400))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, 0) => (411.429, 914.286))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, 0) => (411.429, 313))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, 0) => (411.429, 914.286))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, -501.719) => (411.429, 412.567))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, 0) => (411.429, 914.286))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, 0) => (411.429, 914.286))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((0, -820.286) => (411.429, 94))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((-9.82143, -808.286) => (401.607, 106))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((-88.1786, -825.286) => (323.25, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((-166.536, -825.286) => (244.893, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((-244.893, -825.286) => (166.536, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1164)]   FirstPass cull rect: ((-323.25, -825.286) => (88.1786, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(1369)] Render2Target render cull rect: ((0, 0) => (1080, 2400))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, 0) => (411.429, 914.286))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, 0) => (411.429, 313))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, 0) => (411.429, 820.19))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, -501.719) => (411.429, 318.471))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, 0) => (411.429, 820.19))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, 0) => (411.429, 820.19))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(863)] Skipped 1 RenderTextFrames
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((0, -820.286) => (411.429, 94))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((-9.82143, -808.286) => (401.607, 106))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((-88.1786, -825.286) => (323.25, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((-166.536, -825.286) => (244.893, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((-244.893, -825.286) => (166.536, 89))
E/flutter (25172): [ERROR:flutter/impeller/display_list/dl_dispatcher.cc(825)]   DispatcherBase cull rect: ((-323.25, -825.286) => (88.1786, 89))

@flar

flar commented Feb 19, 2026

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I've implemented a basic workaround for the issue I discovered while debugging the Wondrous behavior. I basically just skip RenderTextFrames until I find one that is appropriate for the call site, but...

  • The comparison should be more complete, checking more than just the pointer identity of the TextFrame
  • This is implemented assuming that the RenderTextFrame list is a superset of what the rendering code needs (which is true for all observed cases, but can't be guaranteed)
  • A more flexible workaround should be implemented that uses a Map and compares more of the critical information used by the glyph atlas.

An interesting side note - if we pass this information as a map then we could save it from frame to frame and avoid having to recompute bounds. Unfortunately, bounds are computed in device space and are sub-pixel based in some cases so this idea would only work for static text that isn't scrolling.

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flar commented Feb 27, 2026

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Closing in favor of a better solution in #182886

@flar flar closed this Feb 27, 2026
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[impeller] TextFrame::SetPerFrameData is weird and possibly buggy

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