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XR Graphics

XR needs to render two images, one for each eye. Therefore, special care needs to be taken when authoring shaders to make sure they support stereo rendering.

Material Shaders

To make a material shader work with stereo rendering, it must contain the following sections:

[PERMUTATIONS]
// Will be set to CAMERA_MODE_STEREO.
CAMERA_MODE

// Defined if the GPU supports setting the render target array index in the vertex shader. If not, a geometry shader will be used.
VERTEX_SHADER_RENDER_TARGET_ARRAY_INDEX

[VERTEXSHADER]
#include <Shaders/Materials/MaterialVertexShader.h>

VS_OUT main(VS_IN Input)
{
  // FillVertexData will set s_ActiveCameraEyeIndex to either 0 or 1. s_ActiveCameraEyeIndex is used in all camera related functions to pull in the correct eye projection / transform etc.
  VS_OUT Output = FillVertexData(Input);
  //...
  return Output;
}

[GEOMETRYSHADER]
// Will only be active if VERTEX_SHADER_RENDER_TARGET_ARRAY_INDEX is not supported.
#include <Shaders/Materials/MaterialStereoGeometryShader.h>

[PIXELSHADER]
// If you use the default MaterialPixelShader.h and just implement GetDiffuseColor() etc then all stereo rendering is done for you. If you write a custom pixel shader, you will need to add this at the start:
//  #if CAMERA_MODE == CAMERA_MODE_STEREO
//    s_ActiveCameraEyeIndex = Input.RenderTargetArrayIndex;
//  #endif
#include <Shaders/Materials/MaterialPixelShader.h>

Postprocessing Shaders

Post-processing shaders are a bit more complicated than material shaders as they usually pull in data from a previous render pipeline pass which will now be an array texture as the input will be stereo as well. Here is a small example of a full-screen render pass and what it requires in order to work in stereo mode:

[PERMUTATIONS]
// Will be set to CAMERA_MODE_STEREO.
CAMERA_MODE

// Defined if the GPU supports setting the render target array index in the vertex shader. If not, a geometry shader will be used.
VERTEX_SHADER_RENDER_TARGET_ARRAY_INDEX

[VERTEXSHADER]
#include <Shaders/Pipeline/FullscreenTriangleVertexShader.h>

[GEOMETRYSHADER]
// Will only be active if VERTEX_SHADER_RENDER_TARGET_ARRAY_INDEX is not supported.
#include <Shaders/Pipeline/FullscreenTriangleStereoGeometryShader.h>

[PIXELSHADER]
#include <Shaders/Pipeline/FullscreenTriangleInterpolator.h>

// Note that this will work fine in non-stereo rendering as well as 2D textures are just 2D-array texture with very few slices.
Texture2DArray Input;

float4 main(PS_IN input) : SV_Target
{
  // To make all camera related functions work correctly, this must be called at the very start to define the right eye.
  #if CAMERA_MODE == CAMERA_MODE_STEREO
    s_ActiveCameraEyeIndex = Input.RenderTargetArrayIndex;
  #endif

  float4 res = Input.Sample(LinearClampSampler, float3(input.TexCoord0, s_ActiveCameraEyeIndex));
  //...
  return res;
}