Triggers the viewPortChanged signal.
QChartViewer may emit viewPortChanged signals when the mouse clicks or drags on the plot area (see QChartViewer.setMouseUsage
). QChartViewer also allows external objects (such as scroll bars, navigation buttons, timers, etc) to modify the viewport. This method allows external objects to request QChartViewer to emit viewPortChanged signals.
Many controls are able to update the viewport continuously as they are used. For example, a scroll bar may update the viewport continuously as the mouse drags on it. For these cases, the chart display may be updated continuously as the viewport changes. However, the image map does not need to update until the scrolling is completed (when the mouse button is released on the scroll bar and the mouse moves over the chart surface ).
argument and needUpdateImageMap
argument allows one to specify if the event requires a chart update, and/or an image map update.
For charts with a lot of hot spots and tool tips, the CPU power needed to handle the image map may not be negligible. Removing unnecessary image map updates may increase the update rate when the chart is being updated continuously.
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