Why using CanvasWidget class to draw lines encounter flicking problem?

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Hi, I encounter a problem to continuously display a physiological waveform through the subclass of CanvasWidget class developed. The dots on the line were added to an FIFO buffer in the subclass within the handleTickEvent() function of the view, then invalidate the corresponding rectangular area with InvalidateRec() function, the drawCanvasWidget() virtual function was reimplementation in the subclass to draw the lines with canvas render class.

But as show in the picture, the lines near to the right border of the widget would flicking continuously. Is there a good way to solve the flicking problem ? Suggestion is needed here.