Ok, so… When you change any effect of a vector sprite, it pixelates a bit!
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Here is an example of the script:
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when green flag clicked
repeat (5)
change [color v] effect by (25)
end
wait (1) secs
stop [all v]

It's due to how scratch calculates the effects. You can toggle it off with a key combination but it's not permanent.

It's because when graphic effects (excluding brightness and ghost) are used, Scratch switches to Stage3D, which has the side-effect of treating vector sprites like bitmap.

(Sources: here, and here)

-ShadowOfTheFuture- wrote:

It's because when graphic effects (excluding brightness and ghost) are used, Scratch switches to Stage3D, which has the side-effect of treating vector sprites like bitmap.

(Sources: here, and here)

Thanks for telling me with info.

when green flag clicked
clear graphic effects
say [Now i know!]
forever
change [color v] effect by (5)
end