Draws a scroll button on a scroll bar control.

在卷轴控制项上绘制卷轴按钮。

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Draws the specified scroll button on a scroll bar control in the specified state, on the specified graphics surface, and within the specified bounds.

在指定的图形表层和指定的范围内，于卷轴控制项上绘制指定状态的指定卷轴按钮。

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This has the further advantage that the scrollbar thumb does not change size over time nor move without user input, making it easier for a user to interact with the scroll bar control.

其进一步的优点在于：滚动条滑动块不随时间改变尺寸，在无用户输入的情况下也不移动，使得用户与滚动条控制部件交互作用更容易。

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