Z.Mat.anglesFromRotationMatrix freezes app

[marks]

Issue: Using the Z.Mat.anglesFromRotationMatrix function described here freezes the app. I attached a sample project with the issue. Please check the LookAt script and lines 50 and 51 of the Placement Preview State script, where I try to use the lookAt function. I commented those lines out because they freeze the app.

Affecting: Zapworks Studio

Workaround: None that I’m aware of.

Instant Tracking (1).zpp (324.9 KB)

[simon]

That’s all pure Javascript so there might be a divide by zero exception or something similar visible in DevTools, perhaps if the thing passed in isn’t actually a rotation matrix. A quick glance at your code looks fine, so might be a bug in the sample code from that forum post or indeed in the anglesFromRotationMatrix code as you say.

Possibly if the two params are identical, as would happen if the intersections weren’t found in a particular frame, then the cross-product ends up as the zero vector, which then is used to define an axis-angle representation. Probably need a special case for 0 rotation in that case.

[marks]

That’s all pure Javascript so there might be a divide by zero exception or something similar visible in DevTools, perhaps if the thing passed in isn’t actually a rotation matrix

I checked the dev tools. It freezes on the anglesFromRotationMatrix code.

[simon]

Thanks for the report - you’re right that the function in the Z library throws an exception at the moment.

You can just include the function locally in your project in a script node though - I’ve posted it over on the “look at” thread you referenced:

Look at behavior + Z.Vec3 and Z.Mat documentation

Thanks for the report, it does indeed look to be broken (the implementation tries to reference Z which is actually a closure variable only available in script nodes - it’s possible this wasn’t the case when the code was written and no one has noticed before, our set of regression tests don’t exercise this function). The simplest approach is just to avoid Z.Mat.anglesFromRotationMatrix() and just include the function locally instead: function anglesFromRotationMatrix(mat, compare?) { if (!c…

Note for Instant Tracking you don’t need to jump through these hoops though, see my reply here:

Introducing Instant Tracking

To get “look at” behaviour there’s a second argument to InstantTracker.setAnchorTransformFromCamera which gives various options for the orientation of the anchor that is placed. My post with the original demo contains the best current documentation for this: Instant Tracking WebAR Beta - Example content and API discussion If you want a placement UI where the content appears at a fixed camera relative position and facing the camera until a “place / lock” button is pressed, then that is accomplis…