[Backport release-3_38] Greatly optimise selective masking vector exports #57839
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Allows us to know in startRender whether the symbol is actually a subsymbol for a QgsSymbolLayer. Currently unused.
Optimise the logic used when the new geometry backend for selective masking is in effect: Whenever its SAFE, instead of calculating an "entire map" clipping path and then applying this for every feature being rendered, we now defer the calculation of the clipping path until we are rendering individual features. Then, we create a clipping path which contains ONLY the mask paths which are within the area being drawn over. This avoids having the entire map clipping path being used for EVERY feature being rendered, which results in huge PDF/SVG exports when masks are in effect, and instead results in clipping paths which are confined just to a sensible area around each rendered feature. In some complex test projects this reduces the PDF export size by a factor of 0.01!! (and results in PDFs/SVGs which open much quicker in viewers and editors, and don't grind their operation to a halt).
These are the symbol layer classes where there's no special logic required relating to feature rendering and features are rendered one-by-one, with no sub symbols.
This is a new opt-in flag for map settings/render context/layouts.
If set, then when applying clipping paths for selective masking,
we always use global ("entire map") paths, instead of calculating
local clipping paths per rendered feature. This results in
considerably more complex vector exports in all current Qt versions,
but gives us a way to force this IF/when a future Qt version adds
optimisations which make global masks desirable.
Instead of the extra argument to startRender
nirvn
approved these changes
Jun 24, 2024
2 tasks
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Backport #57799
Authored by: @nyalldawson