Depth Camera Image to World-Space Position (Unity Compute Shader)

DepthToWorldSpacePositionExample.compute

// This is the old version of my shader - I'm in London atm and don't have the new project that spawns particles to hand
// In this one, there's one particl
// The particles are something like

struct Particle {
    int2 PixelPosition;
    float3 WorldSpacePosition;
}

// compute buffer matched to the particle struct
RWStructuredBuffer<Particle> ParticleBuffer;
// R16 depth texture from RealSense - maybe this could be Texture2D<float> idk lol
Texture2D<float4> DepthTexture;

// transform.localToWorldMatrix of the transform I use to represent the depth camera in the scene
float4x4 TransformMatrix;

// size of the depth texture in pixels
float2 FrameSize;
// literally just FrameSize.x / FrameSize.y - precomputed when we send the texture pointer
float FrameRatio;

// matched to the number of thread groups I call in dispatch - only used for mapping thread ID to particle buffer index
int3 GroupCount;

// Converts raw position into world space position
// X and Y are basically UV coordinates, but I subtract 0.5 so it's centered at 0, 0 at the frame center
// Z is the depth in world-space meters
// W is 1.0 so I can multiply with the transform matrix
float3 GetPos(float4 RawPos, float4x4 TransformMatrix) {
  // Correct for aspect ratio
	RawPos.x *= FrameRatio;
	
  // Project out using depth
  RawPos.x *= RawPos.z;
	RawPos.y *= RawPos.z;

	// Got these values through manual measurement and are specific to the RealSense D435
	RawPos.x *= 1.23134;
	RawPos.y *= 1.23134;

  // Optional, but I have my depth camera mounted on a HMD so this is necessary for me
	RawPos = mul(TransformMatrix, RawPos);
  
	return RawPos.xyz;
}

[numthreads(32, 24, 1)]
void DepthToPositions(uint3 id : SV_DispatchThreadID)
{
	uint idx = id.x + (id.y * 32 * GroupCount.x) + (id.z * 32 * GroupsX * 24 * GroupCount.y);
	Particle CurrentParticle = ParticleBuffer[idx];
  int2 PixelPosition = CurrentParticle.PixelPosition;

  // turns depth texture value (this is from RealSense, so the format is R16 half-precision floating point) into world-space meters
  // this was years ago, but I'm pretty sure I got the multiplier by experimentation via measuring with my vive controllers lol
  float RawDepth = DepthTexture[int2(PixelPosition.x, PixelPosition.y)].x;
  RawDepth *= DepthUnits * DepthScale;

  CurrentParticle.WorldSpacePosition = GetPos(float4(
  	(PixelPosition.x / FrameSize.x) - 0.5,
  	0.5 - (PixelPosition.y / FrameSize.y), //RealSense depth textures are flipped on the y axis
  	RawDepth,
  	1.0
  ), TransformMatrix);
  
  ParticleBuffer[idx] = CurrentParticle;
}