FontainebleauDemo/Assets/Scripts/LensFlare/Shader/LensFlareHDRPCommon.hlsl

struct appdata
{
	float4 vertex : POSITION;
	float2 uv : TEXCOORD0;
	float4 color : COLOR;

	// LensFlare Data : 
	//		* X = RayPos 
	//		* Y = Rotation (< 0 = Auto)
	//		* ZW = Size (Width, Height) in Screen Height Ratio
	nointerpolation float4 lensflare_data : TEXCOORD1;
	// World Position (XYZ) and Radius(W) : 
	nointerpolation float4 worldPosRadius : TEXCOORD2;
	// LensFlare FadeData : 
	//		* X = Near Start Distance
	//		* Y = Near End Distance
	//		* Z = Far Start Distance
	//		* W = Far End Distance
	nointerpolation float4 lensflare_fadeData : TEXCOORD3;
};

struct v2f
{
	float2 uv : TEXCOORD0;
	float4 vertex : SV_POSITION;
	float4 color : COLOR;
};

sampler2D _MainTex;
float _OccludedSizeScale;

// thanks, internets
static const uint DEPTH_SAMPLE_COUNT = 32;
static float2 samples[DEPTH_SAMPLE_COUNT] = {
	float2(0.658752441406,-0.0977704077959),
	float2(0.505380451679,-0.862896621227),
	float2(-0.678673446178,0.120453640819),
	float2(-0.429447203875,-0.501827657223),
	float2(-0.239791020751,0.577527523041),
	float2(-0.666824519634,-0.745214760303),
	float2(0.147858589888,-0.304675519466),
	float2(0.0334240831435,0.263438135386),
	float2(-0.164710089564,-0.17076793313),
	float2(0.289210408926,0.0226817727089),
	float2(0.109557107091,-0.993980526924),
	float2(-0.999996423721,-0.00266989553347),
	float2(0.804284930229,0.594243884087),
	float2(0.240315377712,-0.653567194939),
	float2(-0.313934922218,0.94944447279),
	float2(0.386928111315,0.480902403593),
	float2(0.979771316051,-0.200120285153),
	float2(0.505873680115,-0.407543361187),
	float2(0.617167234421,0.247610524297),
	float2(-0.672138273716,0.740425646305),
	float2(-0.305256098509,-0.952270269394),
	float2(0.493631094694,0.869671344757),
	float2(0.0982239097357,0.995164275169),
	float2(0.976404249668,0.21595069766),
	float2(-0.308868765831,0.150203511119),
	float2(-0.586166858673,-0.19671548903),
	float2(-0.912466347218,-0.409151613712),
	float2(0.0959918648005,0.666364192963),
	float2(0.813257217407,-0.581904232502),
	float2(-0.914829492569,0.403840065002),
	float2(-0.542099535465,0.432246923447),
	float2(-0.106764614582,-0.618209302425)
};

float GetOcclusion(float2 screenPos, float depth, float radius, float ratio)
{
	float contrib = 0.0f;
	float sample_Contrib = 1.0 / DEPTH_SAMPLE_COUNT;
	float2 ratioScale = float2(1 / ratio, 1.0);
	for (uint i = 0; i < DEPTH_SAMPLE_COUNT; i++)
	{
		float2 pos = screenPos + (samples[i] * radius * ratioScale);
		pos = pos * 0.5 + 0.5;
		pos.y = 1 - pos.y;
		if (pos.x >= 0 && pos.x <= 1 && pos.y >= 0 && pos.y <= 1)
		{
			//float sampledDepth = LinearEyeDepth(SAMPLE_TEXTURE2D_LOD(_CameraDepthTexture, sampler_CameraDepthTexture, pos, 0).r, _ZBufferParams);
			float sampledDepth = LinearEyeDepth(SampleCameraDepth(pos), _ZBufferParams);
			
			if (sampledDepth >= depth)
				contrib += sample_Contrib;
		}
	}
	return contrib;
}

v2f vert(appdata v)
{
	v2f o;

	float4 clip = TransformWorldToHClip(GetCameraRelativePositionWS(v.worldPosRadius.xyz));
	float depth = clip.w;

	float3 cameraUp = normalize(mul(UNITY_MATRIX_V, float4(0, 1, 0, 0))).xyz;

	float4 extent = TransformWorldToHClip(GetCameraRelativePositionWS(v.worldPosRadius.xyz + cameraUp * v.worldPosRadius.w));

	float2 screenPos = clip.xy / clip.w;
	float2 extentPos = extent.xy / extent.w;

	float radius = distance(screenPos, extentPos);

	float ratio = _ScreenParams.x / _ScreenParams.y;
	float occlusion = GetOcclusion(screenPos, depth - v.worldPosRadius.w, radius, ratio);

	// Distance Fade
	float4 d = v.lensflare_fadeData;
	float distanceFade = saturate((depth - d.x) / (d.y - d.x));
	distanceFade *= 1.0f - saturate((depth - d.z) / (d.w - d.z));

	// position and rotate
	float angle = v.lensflare_data.y;
	if (angle < 0) // Automatic
	{
		float2 dir = normalize(screenPos);
		angle = atan2(dir.y, dir.x) + 1.57079632675; // arbitrary, we need V to face the source, not U;
	}

    // apply size
    float2 quad_size = lerp(_OccludedSizeScale, 1.0f, occlusion) * v.lensflare_data.zw;
    if (distanceFade * occlusion == 0.0f) // if either one or other is zeroed
        quad_size = float2(0, 0); // clip

	float2 local = v.vertex.xy * quad_size;

	local = float2(
		local.x * cos(angle) + local.y * (-sin(angle)),
		local.x * sin(angle) + local.y * cos(angle));

	// adjust to correct ratio
	local.x /= ratio;

	float2 rayOffset = -screenPos * v.lensflare_data.x;
	o.vertex.w = v.vertex.w;
	o.vertex.xy = screenPos + local + rayOffset;

	o.vertex.z = 1;
	o.uv = v.uv;

	o.color = v.color * occlusion * distanceFade * saturate(length(screenPos * 2));
	return o;
}