java - Swing paint issue

Question

I have a custom scrollbarUI which I paint both thumb and track of scrollbar. But when scrolling it keeps some lines like below which I don't want. :

Painting code is below:

protected void paintThumb(Graphics g, JComponent c, Rectangle thumbBounds) {
    Graphics2D g2d = (Graphics2D) g;

    GradientPaint gradient = new GradientPaint(new Point(thumbBounds.x, thumbBounds.y), gray, new          Point(thumbBounds.x + width, thumbBounds.y), white);

    g.setColor(white);
    g.fillRoundRect(thumbBounds.x + 1, thumbBounds.y + 1, thumbBounds.width - 3, thumbBounds.height - 1, 2, 2);

    g2d.setPaint(gradient);
    g2d.fillRoundRect(thumbBounds.x + 2, thumbBounds.y + 2, thumbBounds.width - 4, thumbBounds.height - 3, 3, 3);

    //Draw middle lines:
    if ((getMinimumThumbSize().height + 10) < thumbBounds.height) {
        g.setColor(new Color(167, 167, 167));
        int w = ((thumbBounds.width > 16) ? 8 : (int) ((thumbBounds.width / 2.0) + 0.5));
        int x = (thumbBounds.width > 0) ? (thumbBounds.x + ((thumbBounds.width - w) / 2) - 1) : thumbBounds.x;

        g.drawLine(x, (thumbBounds.y + (thumbBounds.height / 2) - 3), (x + w), (thumbBounds.y + (thumbBounds.height / 2) - 3));
        g.drawLine(x, (thumbBounds.y + (thumbBounds.height / 2) - 1), (x + w), (thumbBounds.y + (thumbBounds.height / 2) - 1));
        g.drawLine(x, (thumbBounds.y + (thumbBounds.height / 2) + 1), (x + w), (thumbBounds.y + (thumbBounds.height / 2) + 1));
    }

    g.setColor(color_1);
    g.drawRoundRect(thumbBounds.x, thumbBounds.y, thumbBounds.width - 2, thumbBounds.height, 2, 2);
}

Answer 1

你需要使用

g.drawRoundRect(..., thumbBounds.height - 1, 2, 2) 

代替

g.drawRoundRect(..., thumbBounds.height, 2, 2)

的底边drawRoundRect(x,y,width,height,arcW,arcH)位于y + height，但 的底边repaint(thumbBounds)位于thumbBounds.y + thumbBounds.height - 1。所以 1px 线保持没有重绘。