Responsive cancellation of paint effects #45212
Merged
Conversation
This file contains 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
This was a historic artefact from the time before QgsMapLayerRenderer::feedback existed
for cancelation check support While there is the existing QgsRenderContext::renderingStopped() check, this doesn't play well with other parts of QGIS which utilise a QgsFeedback object for cancelation support. By adding support for a proper QgsFeedback object in render contexts then it becomes trivial to pass this on to feature requests, expression contexts, and other potentially expensive functions so that these can all be canceled responsively too. (At some stage in the future we should consider deprecating QgsRenderContext::rendereringStopped(), but that's not done here)
…renderer feedback This gives rendering subcomponents (symbols, etc) access to the layer renderer's feedback object for cancelation checks
responsive cancelation of operations
Ultimately this means that the (potentially very expensive) image operations can be aborted quickly when a map render job is canceled. It avoids having background threads burning away trying to perform the blur operations for map views we no longer want anymore. Refs qgis#41149
nirvn
approved these changes
Sep 24, 2021
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Outdated suggestions cannot be applied.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.
This PR adds support for responsive cancelation of paint effects. These can potentially be very expensive to calculate, especially when a user accidentally sets a too-large blur radius or similar. Previously this would cause QGIS to burn away cpu in background threads trying to calculate the paint effect, even for map render jobs which had been canceled.
Now, we proxy the map layer renderer's QgsFeedback object through QgsRenderContext to the QgsDrawEffect/QgsImageOperation methods, so that the expensive code paths in these classes have a way to test if the render is canceled and they should early exit.
Refs #41149, but doesn't fix that issue (it's still possible to hang the UI for large periods of time if excessive blur radius are set for symbols, as the layer tree and symbol preview icon generation are run in the main thread and have no way to cancel these renders. In order to fully fix the bug we'd also need to implement limits on the blur sizes used for these symbol icons)