Why my simulator has a white line on screen？

General discussion
1

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this based on a canvas of the whole screen。When I press the top button, as long as the mouse stays in the window, there will be a white line, but this will not change if I press the button and move the mouse out of the window 。

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  • The buttons are transparent in style, built on the canvas。
2

Without knowing the details of your implementation it seems like an off-by-one issue in y (or height) somewhere.
E.g. is y1 = 20, y2=30 is 11 px not 10 px.

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