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Technical documentation

Selecting a timeslice and a datastock

Users can select the time range and a single datastock on the chart.

The time range is a TimeSlice.

Both informations are saved in selectedTimeSlice and selectedData properties of the StockChart struct. These values reflects the selection in request for a drawing. That means these values are used by the drawing process.

They can be updated through an user interaction with the chart, like clicking on a data or changing the navebar selector, or they can be updated through an external request.

xAxisRange

xAxisRange is the timeslice used by drawings, it's pointing to 2 kind of ranges according to layers:

layer xAxisRange Comment
1-navbar &chart.timeRange
2-timeselector &chart.timeRange
3-DrawingYGrid &chart.selectedTimeSlice
4-chart &chart.selectedTimeSlice SubChart used the same xAxisRange
5-hover &chart.selectedTimeSlice

Is there any selection ?

selectedTimeSlice.IsZero() means there's no selected time range, which may occurs for an empty chart, otherwise the selected timeslice is always defined with valid boundaries.

For the selectedData it's different, this is a pointer. A nil value indicate ther's no selection otherwise it points directly to the DataStock within the series.

Initial Update

SetTimeRange() is called to setup the global time range of the chart. It's called at least during the chart creation and can be set later.

- SetTimeRange()
    - if selchange is required
        - DoChangeSelTimeSlice()
            - UPDATE `selectedTimeSlice` in the chart
            - RedrawOnlyNeeds() 
                - for each layer
                    - RedrawOnlyNeeds() 
                        - for each drawing
                            - if at least one drawing needs a redraw (call to NeedRedraw())
                                - Redraw() all the layer
                        - update selection on the layer with the selection at the chart level `selectedTimeSlice` & `selectedData`
            - if notify requested
                - NotifySelChangeTimeSlice()

If drawings on layers are not created when calling SetTimeRange has no effect. Each drawing will get the chart selection data to redraw themselves.

Update from outside of the chart

DoChangeSelTimeSlice() and DoChangeSelData() redraw all drawings if any change occured.

Update with user interacting with the chart

Drawings uses drawing.xAxisRange and chart.selectedData for a redraw.

Some drawings can update chart.selectedData or selectedTimeSlice according to user interactions.

At the end of the drawing process, the event dispatcher will detect a change in selectedTimeSlice or selectedData and will propagate a DoChangeSelTimeSlice() and DoChangeSelData() at the chart level to redraw layers that needs to.

Propagation of changes to other layers and other drawings

To enable user interaction with drawings SetEventDispatcher() must have been called initially on the layer. Then every drawing must implement one or more On{event}() function. For the time behing two layers are dispatching events:

  • 2-timeselector layer: user can change the selected timeslice
  • 5-hover layer: user can select a single data point

For these layers all mouse events are activated on the canvas. When an event occurs on the canvas it's dispatchd to all drawings having implemented the On{event}() function. When leaving this function the dispatcher checks if any selection have changed during the drawings. If any change occurs, the dispatcher calls DoChangeSel{timesllice|data}() on the chart only one time.

layer chart xAxisRange Dispatch
1-navbar DrawingSeries &chart.timeRange no
1-navbar DrawingXGrid(not time dep.) &chart.timeRange no
2-timeselector DrawingTimeSelector &chart.timeRange Yes (1)
3-DrawingYGrid DrawingYGrid &chart.selectedTimeSlice no
4-chart DrawingBackground &chart.selectedTimeSlice no
4-chart DrawingYGrid &chart.selectedTimeSlice no
4-chart DrawingXGrid(time dep.) &chart.selectedTimeSlice no
4-chart DrawingBars &chart.selectedTimeSlice no
4-chart DrawingCandles (subchart) &chart.selectedTimeSlice no
4-chart DrawingCandles (mainchar) &chart.selectedTimeSlice no
5-hover DrawingHoverCandles &chart.selectedTimeSlice Yes (2)

(1) Dispatch on the timeselctor

  • OnRedraw() : uses drawing.chart.selectedTimeSlice for the dragtimeSelection
  • OnMouseUp() : chart.selectedTimeSlice is updated with the user selection
  • OnWheel() : chart.selectedTimeSlice is updated according to shift and zoom

(2) Dispatch on the hover

  • OnClick() : chart.selectedData is updated with the user selection

RedrawOnlyNeeds

The RedrawOnlyNeeds process is used to optimze redrawing.

DoChange[SelTimeslice|SelData|Timezone]()
    Update chart data
    RedrawOnlyNeeds() 
        scan all layers
            scan all drawings
            if at least one drawing.NeedRedraw() on the layer
                then Redraw() the layer
                    scan all drawings
                        call OnRedraw() on each layer

    if func is defined, NotifyChange[SelTimeslice|SelData] func

To answer to NeedRedraw(), each drawing need to compare their local data with the chart data. If the function is not implemented then the layer consider that the drawing do NOT need a redraw, this is the case for layer not dependant on chart selection.

layer chart NeedRedraw Implemented NeedRedraw
1-navbar DrawingSeries Yes SelectedData changed
1-navbar DrawingXGrid(not time dep.) Yes localZone changed
2-timeselector DrawingTimeSelector YES dragtimeSelection no more equal to chart.selectedTimeSlice
3-DrawingYGrid DrawingYGrid YES yrange(chart.selectedTimeSlice) changed
4-chart DrawingBackground No No
4-chart DrawingYGrid YES yrange(chart.selectedTimeSlice) changed
4-chart DrawingXGrid(time dep.) Yes localZone changed OR SelectedTimeSlice changed
4-chart DrawingBars Yes SelectedTimeSlice changed
4-chart DrawingCandles (subchart) Yes SelectedTimeSlice changed OR SelectedData changed
4-chart DrawingCandles (mainchar) Yes SelectedTimeSlice changed OR SelectedData changed
5-hover DrawingHoverCandles No No

All Drawing's series are pointing to the main series referenced at chart level, unless for subchart. This main series are updated by RsetMainSeries().

NOTA: OnRedraw redraw all drawings without exception