[Interest] Qt3D - QObjectPicker & back-face culled entities

[Sean Harmer]

On Wednesday 07 December 2016 13:03:26 Philip Schuchardt wrote:
> It doesn't appear to be supported in the current documentation (5.7).
> Another way to solve this is by rendering each object with a unique picking
> color and the querying the pixel color under the mouse.  This could
> probably be done by setting up a framegraph and use a RenderCapture
> (although, I haven't gotten a RenderCapture to work).  With this
> method, back-face culled entities will be handled correctly. One downside
> to this method is that you'll only be able to query the closest pixel. I
> guess you could do something like depth peeling to get other pixels, but
> seem a bit extreme. With the pixel-based approach, you can improve
> performance by reducing the size of the viewport. Reducing the size trades
> off accuracy for performance by the way. For example squishing a 1000 x
> 1000 pixel viewport into 10 x 10 pixel viewport would give you good raster
> performance but your picking wouldn't be very accurate.
> 
> Perhaps adding a flag to QPickerSetting to support back-face culling would
> be a nice feature. Have you looked in Qt bug tracker?

That's coming in 5.8. Just need to check it's working as expected...

> Also, is the triangle picking is accelerated in any way? Or does the
> algorithm just brute force through all the triangles?

Does a broad phase check on bounding spheres first. Then traverses triangles.

Cheers,

Sean

> 
> On Wed, Dec 7, 2016 at 12:41 AM Andy <asmaloney at gmail.com> wrote:
> > (Since I didn't get any response from my last question about picking I
> > thought I'd try asking it in a different way.)
> > 
> > How do I prevent the object picking mechanism from "seeing" back-face
> > culled entities so that it picks entities based on what the user is
> > actually seeing in the scene?
> > 
> > Thank you!
> > 
> > ---
> > Andy Maloney  //  https://asmaloney.com
> > twitter ~ @asmaloney <https://twitter.com/asmaloney>
> > 
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