Passthrough Windows

If your virtual scene fills the entire screen, for example, because you are in a room or you want to use a skybox, you can create windows through which passthrough is visible by modifying the framebuffer’s alpha channel after everything else has been rendered. Writing an alpha value of zero to a certain region of the screen will allow passthrough to shine through the virtual scene completely in that location. Writing an alpha value between zero and one will create a blend between passthrough and VR. Originally, it was advised to configure the application’s framebuffer to use non-premultiplied alpha by setting OVRManager.eyeFovPremultipliedAlphaModeEnabled = false; to ensure that the framebuffer’s color values were correctly multiplied with the alpha value during compositing. Nowadays, this is no longer necessary as the shader now uses multiplicative blending, which eliminates the need for runtime settings adjustments.

Note: If depth testing is enabled when rendering the passthrough window objects, they will be properly occluded by virtual objects in front of them. The occlusion happens based on the depth of the passthrough window geometry, not based on the real-world depth of the content seen through it.