Laser Pointer Visibility Over Passthrough on Zapbox

[apzap]

Description

The laser pointer line fails to display properly when using Open-Brush with the Zapbox XR provider. Specifically, the laser pointer is not visible when it appears over the passthrough background. This differs from the expected behaviour seen on Quest devices, where the laser pointer remains visible regardless of the background.

Environment

• Unity Version: 2022.3.34f1
• Build Target: iOS
• XR Provider: Zapbox
• Application: Open-Brush

Steps to Reproduce

1. Set up the project with Zapbox as the XR provider
2. Resolve any material-related errors in the project
3. Launch the application
4. Complete the tutorial section
5. Point the controller at any panel where the dashed laser pointer should appear
6. Observe the laser pointer behaviour when it crosses over passthrough areas

Expected Behaviour

The laser pointer line should remain visible when pointing at any surface, including when the line passes over passthrough areas, similar to how it functions on Quest devices.

Actual Behaviour

The laser pointer line appears invisible when it is over areas where passthrough is displayed.

Project Configuration

• No custom modifications to the standard setup

Additional Context

I've attached some video and screenshots from a capture.

openbrush-alpha.mov

Possible Solution

This is a suggested solution. I’ve modified the shader so that alpha is controlled only from the surface function which sets the colour as a premultiplied alpha. https://github.com/apzap/open-brush/tree/fix/laserpointer-fix-zapbox

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Checklist

• I have checked for similar issues
• I have included all relevant information
• I have included clear reproduction steps
• I have tested with the latest Unity version

[andybak]

PR: #828

Build: https://github.com/icosa-foundation/open-brush/actions/runs/13498837311#artifacts

We'll need to do a bit of testing on other platforms to make sure there's no side effects.