This cairo-(vbRichClient5)-dependent Demo will show (as the Title says) - how to efficiently
implement a scenario, where you have to manage "connectable, draggable Boxes"
(as in the Graph in the following screenshot):
![]()
There's a green highlighted Connection (with an appropriate ToolTip), which can - (especially
when the Path is complex) - often cause headaches with regards to: "how-to-implement".
With cairo we have two nice calls available, which can help a great deal, when solving
such more challenging "HitTest-problems":
- cCairoContext.InFill(x, y)
- cCairoContext.InStroke(x, y) <-- this one was used in the Demo
So, what one basically has to do to accomplish a complex HitTest is, to simply apply the Path
in question onto a CairoContext with the appropriate coordinates "as when truly rendered".
Even better, such a cairo-context doesn't have to be derived from "something physically"
(as e.g. a larger ImageSurface), a "virtual one" is already sufficient for that task.
For that purpose (when working with the WidgetEngine, as in this Demo) - each cWidgetBase
already offers such a context over W.MeasureContext.
A slight problem I found was, that whilst CC.InFill always worked reliably, CC.InStroke was only
delivering reliable Hits in 80-90% on the length of a complex Path (as e.g. the Beziers I used here,
due to rounding-errors in the cairo-C-Source).
Though I found a patch for that in the cairo-repo and backported that to the version (vb_cairo_sqlite.dll)
which comes with the RichClient - in consequence CC.InStroke will now work equally reliable as CC.InFill.
So the version of the RichClient (including the latest compile of vb_cairo_sqlite.dll) which will work
well with the zipped Demo-Archive below, needs to be at least 5.0.24 - please visit the Download-
page at vbRichClient.com and update your package appropriately before running it.
Here's the Demo-Zip:
WidgetGraphConnections.zip
Have fun...
Olaf
implement a scenario, where you have to manage "connectable, draggable Boxes"
(as in the Graph in the following screenshot):
There's a green highlighted Connection (with an appropriate ToolTip), which can - (especially
when the Path is complex) - often cause headaches with regards to: "how-to-implement".
With cairo we have two nice calls available, which can help a great deal, when solving
such more challenging "HitTest-problems":
- cCairoContext.InFill(x, y)
- cCairoContext.InStroke(x, y) <-- this one was used in the Demo
So, what one basically has to do to accomplish a complex HitTest is, to simply apply the Path
in question onto a CairoContext with the appropriate coordinates "as when truly rendered".
Even better, such a cairo-context doesn't have to be derived from "something physically"
(as e.g. a larger ImageSurface), a "virtual one" is already sufficient for that task.
For that purpose (when working with the WidgetEngine, as in this Demo) - each cWidgetBase
already offers such a context over W.MeasureContext.
A slight problem I found was, that whilst CC.InFill always worked reliably, CC.InStroke was only
delivering reliable Hits in 80-90% on the length of a complex Path (as e.g. the Beziers I used here,
due to rounding-errors in the cairo-C-Source).
Though I found a patch for that in the cairo-repo and backported that to the version (vb_cairo_sqlite.dll)
which comes with the RichClient - in consequence CC.InStroke will now work equally reliable as CC.InFill.
So the version of the RichClient (including the latest compile of vb_cairo_sqlite.dll) which will work
well with the zipped Demo-Archive below, needs to be at least 5.0.24 - please visit the Download-
page at vbRichClient.com and update your package appropriately before running it.
Here's the Demo-Zip:
WidgetGraphConnections.zip
Have fun...
Olaf