BCGCBPRODLLEXPORT UINT BCGM_ON_CHART_LEGEND_MOUSE_DOWN

The framework sends the BCGM_ON_CHART_LEGEND_MOUSE_DOWN message when the legend visual object receives a mouse button down notification.

Parameters

wParam	mouse button number (0 - left, 1 - right, 2 - middle).
lParam	a pointer to a BCGPChartLegendHitInfo structure.

Returns

TRUE - disable further mouse down processing. In this case a legend scrolling (if available) will not occur.

You should process this message to implement interactive chart legend.