🐛 Clear the transform effect's scratch canvas between frames - #363
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The scratch canvas is only reset when the target is resized, so on a steady-size movie it is never cleared. drawImage composites source-over, so the previous transformed frame survived wherever the current one was transparent and was copied back onto the target, leaving a trail behind a moving layer. Clear it before compositing, resetting the transform to identity first so the clear is not mapped through the last frame's matrix. That reset replaces the one at the end of apply, whose arguments were in the wrong order: setTransform(1, 0, 0, 0, 1, 0) has d = 0, so it was degenerate rather than identity.
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Fixes #286.
The scratch canvas the effect composites through is only reset when the target is resized, so on a steady-size movie it's never cleared.
drawImagecomposites source-over, so the previous transformed frame survives wherever the current one is transparent and gets copied back onto the target — the trail @keiddzz reported.This clears the scratch canvas before compositing, resetting the transform to identity first so the clear isn't mapped through the last frame's matrix. That reset replaces the one that was at the end of
apply, whose arguments were in the wrong order:setTransform(1, 0, 0, 0, 1, 0)hasd = 0, so it was degenerate rather than identity.Added a unit test that applies the effect over two frames and asserts the old position is empty — it fails on master and passes here. I also reproduced @keiddzz's setup end to end (an
Imagelayer with a keyframed matrix, rendered across four frames) and confirmed the trail is gone. Existing unit, smoke and integration suites all pass.