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Single-pass stereo rendering for Android

Explains how to use single-pass stereo rendering in your Android application.
Read time 2 minutesLast updated 10 days ago
Unity supports single-pass stereo rendering for Android devices that support multiview. Multiview consists of the GL_OVR_multiview2 and GL_OVR_multiview_multisampled_render_to_texture OpenGL ES extensions. These extensions require shaders to use a 2D texture array that consists of two slices, one slice per eye.

Shader code requirements

To use single-pass stereo rendering with custom shaders, you may need to include additional shader code. You don't need to include additional code if your custom shaders are:
  • Surface Shaders that don't have custom vertex processing.
  • Fixed-function pipeline shaders.
Note
These shader changes are compatible with multi-pass stereo rendering.

Modify your shaders

If you want to use the 
unity_StereoEyeIndex
built-in shader variable to know which eye the GPU is rendering to, you must declare 
UNITY_VERTEX_OUTPUT_STEREO
in any shader stage output structs that you have. For example:
struct v2f {    float2 uv : TEXCOOR0;    float4 vertex : SV_POSITION;    UNITY_VERTEX_OUTPUT_STEREO};
To initialize the output data, use 
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO()
in the vertex shader function. For example:
v2f vert (appdata v){	v2f o;	UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);    o.vertex = UnityObjectToClipPos(v.vertex);    o.uv = TRANSFORM_TEX(v.uv, _MainTex);    return o;}
To initialize 
unity_StereoEyeIndex
in subsequent stages, add 
UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX()
at the beginning. For example:
half4 frag (v2f i) : SV_Target{    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);	// sample the texture	half4 col = tex2D(_MainTex, i.uv);	// apply fog	UNITY_APPLY_FOG(i.fogCoord, col);	return col;}
If your shaders use other shader stages, use the 
UNITY_TRANSFER_VERTEX_OUTPUT_STEREO()
macro to transfer the eye index to the subsequent stages.
Tip
To calculate the final position of the object, it's best practice to use 
UnityObjectToClipPos(IN.vertex)
instead of 
mul(UNITY_MATRIX_MVP, IN.vertex)
.

Post-Processing Shaders

You must update post-processing shaders to deal with the eye textures being a 2D texture array. To help with this, Unity includes the 
UNITY_DECLARE_SCREENSPACE_TEXTURE()
macro. To make textures work in both multi-pass and single-pass modes, wrap each textures in this macro. Also, when you sample the texture, use the 
UNITY_SAMPLE_SCREENSPACE_TEXTURE()
macro.
This macro requires that you call 
UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX()
beforehand when in single-pass mode. Unity also includes similar macros for depth textures and screen space shadow maps. You can see the full list at the bottom of 
HLSLSupport.cginc
.