UnityCameraCrossFade

A very simple demo using a render texture and the ScreenOverlay image effect to cross fade between two cameras. This particular setup allows one to cross-fade between two meshes without worrying about the usual z-depth rendering issues.

A few solutions I saw floating around are pretty old and avoid using Render Textures because they used to be only avalable in the paid version. Also, they use OnGUI to render the RT full screen, which immediately made my laptop fan go to full blast. So, here is an alternative.

Scene Setup

The demo scene uses two cameras, one of which can see a cube, the other a sphere. Both cameras see the rest of the scene. This is done using layers and the Camera culling settings. This way, the other objects in the scene do not appear to change.

The fade button simply triggers an animation that interpolates the intensity field of the ScreenOverlay image effect.

Render Texture

For this scene, the RenderTexture was created in the editor and assigned to the second camera. In practice, it would probably be better to do this via script and creating a RT for the current resolution of the application.

Once Camera2 is set to render to the texture, it needs to be sent to the ScreenOverlay Component. However, as far as I can tell, we must copy the RT into a normal texture (I suspect the ScreenOverlay and the shader it uses could be modified to directly use the RT and save a costly copy?). This is done with the following (see Assets/CameraRTBehavior.cs):

RenderTexture.active = renderTexture;
texture.ReadPixels (new Rect (0, 0, texture.width, texture.height), 0, 0);
texture.Apply ();

where texture is a reference to the ScreenOverlay texture and renderTexture is a reference to Camera2's render target.

CutoutOverlay Image Effect/Shader

This is based on the ScreenOverlay image effect from standard assets. It takes an extra texture that it uses with the Cutout Threshold. The cutout threshold determines the minimum alpha value to be considered opaque in the overlay image. The Blend Size parameter defined how far on either side of the cutoff the two images should be alpha blended together.