WpfGfx: Fix headless RenderTargetBitmap rendering#11467
Open
etvorun wants to merge 1 commit intodotnet:mainfrom
Open
WpfGfx: Fix headless RenderTargetBitmap rendering#11467etvorun wants to merge 1 commit intodotnet:mainfrom
etvorun wants to merge 1 commit intodotnet:mainfrom
Conversation
- Preserve existing default partition-thread render behavior - Allow UI-thread synchronous compose path to render without display devices - Keep compatibility switch behavior unchanged
dotnet-policy-service
bot
added
the
PR
Contributor
There was a problem hiding this comment.
Pull request overview
This PR addresses a headless rendering gap in WpfGfx where RenderTargetBitmap-style synchronous (UI-thread) composition could produce blank output when no display devices are available, by threading an explicit “render even without displays” flag through the compose pipeline.
Changes:
- Added a
canRenderWithoutDisplayDevicesparameter to thePartition::Compose/CComposition::Compose/CComposition::ProcessCompositioncall chain. - Updated
CComposition::ProcessCompositionto allow a render pass when this flag is set (in addition to the existing compatibility switch). - Enabled the flag only for the same-thread (UI-thread) present path; partition-thread rendering continues to pass
false.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/partitionthread.cpp | Passes false for regular partition-thread rendering and documents the AppContext switch behavior. |
| src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/partition.h | Updates Partition::Compose signature to accept the new flag. |
| src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/connectioncontext.cpp | Passes true for same-thread synchronous compose used by RenderTargetBitmap-style rendering. |
| src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/composition.h | Threads the new flag through CComposition::Compose and ProcessComposition declarations. |
| src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/composition.cpp | Uses the new flag to override render-pass skipping when display state is invalid. |
Comments suppressed due to low confidence (1)
src/Microsoft.DotNet.Wpf/src/WpfGfx/core/uce/composition.cpp:654
- In the WGXERR_DISPLAYSTATEINVALID path,
NotifyDisplaySetChangeexpects theinvalidflag (true when the display set is invalid). PassingdoRenderPasshere appears inverted relative to the comment: whencanRenderWithoutDisplayDevicesis true, we likely want to lie to targets that the display set is valid (invalid = false) so they don't release resources/invalidate; whendoRenderPassis false we wantinvalid = trueto notify targets of the invalid display set. Consider passing!doRenderPass(or an explicitinvalidDisplaySetvariable) instead ofdoRenderPass.
// and notify any listeners that display set is not valid
// If the UI thread has requested that we try to render despite this,
// then override and lie to listeners that displays are valid.
IFC(m_pRenderTargetManager->NotifyDisplaySetChange(doRenderPass, displayCount));
GetVisualCacheManagerNoRef()->NotifyDeviceLost();
💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.
|
|
||
| MIL_THR(pServerEntry->pCompDevice->Compose(&fPresentNeeded)); | ||
| // So far this method is used only to synchronously present on managed UI | ||
| // thread when calling RenderTargetBitmap.Render or alike. This can happen |
There was a problem hiding this comment.
Grammar nit in the new comment: "RenderTargetBitmap.Render or alike" is awkward/incorrect English. Consider changing to "RenderTargetBitmap.Render or similar" (or "and similar APIs").
Suggested change
| // thread when calling RenderTargetBitmap.Render or alike. This can happen | |
| // thread when calling RenderTargetBitmap.Render or similar APIs. This can happen |
|
|
||
| // This code path is for regular WPF rendering. By default we do not allow | ||
| // rendering without display devices being present. App authors can still | ||
| // allow that with following switch in their app config file: |
There was a problem hiding this comment.
Grammar nit in the new comment: "allow that with following switch" reads like a typo. Consider "allow that with the following switch" for clarity.
Suggested change
| // allow that with following switch in their app config file: | |
| // allow that with the following switch in their app config file: |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
Fixes a rendering gap where
RenderTargetBitmapcould produce blank output when no display devices are attached.What changed
canRenderWithoutDisplayDevicesto compose pipeline signatures.CComposition::ProcessCompositionto allow rendering when this flag is set.RenderTargetBitmap-style rendering.falsethere (compat switch behavior remains available).Why
The composition pass may skip rendering when display state is invalid. For the UI-thread bitmap rendering path, this caused blank image output in headless/disconnected environments. The change provides a targeted override for that path without broadening default behavior.
Validation
Manual-only validation by repository owner.
Fixes #11466
Microsoft Reviewers: Open in CodeFlow