[X3D-Public] What is the behavior of Touch/Drag sensors when occluded?

Bederov, Sergey bederov at cortona3d.com
Sat May 12 02:13:25 PDT 2012

Hello Dave,

Handling of transparent textures is explicitly defined in specification:


"The appearance properties of the geometry do not affect activation of the sensor. In particular, transparent materials or textures shall be treated as opaque with respect to activation of pointing-device sensors."

Though, there is some ambiguity about shapes without sensors:


"In all cases the pointer is considered to be indicating a specific geometry when that geometry is intersected by the bearing. If the bearing intersects multiple sensors' geometries, only the sensor nearest to the pointer will be eligible for activation."

In other words, if the ray intersects multiple shapes with sensors, the nearest one is picked; but it's not clear what to do if there is a shape without sensors and it happens to be the nearest one.

Cortona3D Viewer (and, I believe, most VRML and X3D browsers) interpret it as "the geometry nearest to the pointer". First, the geometry nearest to the camera is determined; second, it is checked whether this geometry has any active sensors attached. If the nearest geometry doesn't have sensors, no sensors are activated.

Probably the specification needs to be clarified?

                                                     Sergey Bederov

> -----Original Message-----
> From: x3d-public-bounces at web3d.org [mailto:x3d-public-bounces at web3d.org] On
> Behalf Of Dave A
> Sent: Saturday, May 12, 2012 11:15 AM
> To: x3d-public at web3d.org
> Subject: [X3D-Public] What is the behavior of Touch/Drag sensors when
> occluded?
> Let's say you have an object that has a TouchSensor on it. It happens to be
> behind a (let's say) semi-transparent object. Maybe that material has a
> texture that looks like chain-link fence or maybe it's a window.
> Should I be able to touch it?
> I don't see anything in the spec that really addresses this.
> What I would hope for in a knee-jerk way is, it would let me pick 'through'
> transparent textures. But I realize this is a dicey proposition to make a
> blanket rule.
> So my next thought is that it would let me pick through anything that
> doesn't also have a sensor like that on it. But again, easy to find examples
> of why that's not good.
> So ultimately, what I expect, is some sort of boolean or node or something
> that says 'ignore for picking' or something to that effect.
> Anyone know if Contact has such an option?
> Dave A
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