Hi,
being aware this is an old post, im adding in my take on this in case someone is has the same question.
i had the same problem. my scenario was i have 2 measures over time i plot as a line chart. one is an actualand one is a forecast. the user wants to see actuals as a solid line and forecast as a dashed line and a vertical line where the actual transitions to forecast.
i created a variable that will hold the date delineating the two measures. i created a combo chart with 4 expressions. first expression, i had something like this: =sum({<[Date]={"<=$(vDate)"}>}Actual) line style to <S1> solid, where vDate is a variable for selected date. 2nd measure:=sum({<[Date]={"<=$(vDate)"}>}Forecast) line style <S3> broken. for my 3rd expression, i used a bar chart =sum({<[Date]={"<=$(vDate)"}>}Actual-100); 4th expression: =sum({<[Date]={"<=$(vDate)"}>}Forecast-Actual+200); i set the bar style to STACKED and selected allow thin bars. color of first bar is 100% transparent; color of 2nd bar is solid which gives the appearance of a floating vertical line.
then i set a trigger on date selection to save the max selected date to the variable vDate and then clear the field Date
what this did was plot actuals as solid up to the date selected then plot forecast (it jumps on the selected date) as dashed. the vertical line is a very thin bar chart at the transition. i added the -100 and +200 so the bar chart is 100 points below Actual and ends 200 points above forecast. the user can click on any part of the line which will trigger a Date selection and move the bar; the scenario is for Forecast always greater than actuals. if not, then its easy to twaek the bar charts depending on which one is higher and which is lesser. hope this helps someone.
