vec3 packNormalToRGB( const in vec3 normal ) {
  return normalize( normal ) * 0.5 + 0.5;
}

vec3 unpackRGBToNormal( const in vec3 rgb ) {
  return 1.0 - 2.0 * rgb.xyz;
}

const float PackUpscale = 256. / 255.; // fraction -> 0..1 (including 1)
const float UnpackDownscale = 255. / 256.; // 0..1 -> fraction (excluding 1)

const vec3 PackFactors = vec3( 256. * 256. * 256., 256. * 256.,  256. );
const vec4 UnpackFactors = UnpackDownscale / vec4( PackFactors, 1. );

const float ShiftRight8 = 1. / 256.;

vec4 packDepthToRGBA( const in float v ) {

	vec4 r = vec4( fract( v * PackFactors ), v );
	r.yzw -= r.xyz * ShiftRight8; // tidy overflow
	return r * PackUpscale;

}

float unpackRGBAToDepth( const in vec4 v ) {

	return dot( v, UnpackFactors );

}

// NOTE: viewZ/eyeZ is < 0 when in front of the camera per OpenGL conventions

float viewZToOrthographicDepth( const in float viewZ, const in float near, const in float far ) {
  return ( viewZ + near ) / ( near - far );
}
float orthographicDepthToViewZ( const in float linearClipZ, const in float near, const in float far ) {
  return linearClipZ * ( near - far ) - near;
}

float viewZToPerspectiveDepth( const in float viewZ, const in float near, const in float far ) {
  return (( near + viewZ ) * far ) / (( far - near ) * viewZ );
}
float perspectiveDepthToViewZ( const in float invClipZ, const in float near, const in float far ) {
  return ( near * far ) / ( ( far - near ) * invClipZ - far );
}