/**
*
* \brief Godrays_*.cg is a radial blur based shader implementation of the natural effects of godrays (ray light scattering). The vertex function ScreenQuadVS() skips the default wvp-transform, what is irrelevant in Ogre when doing a "render_quad"-pass... just to say!
*
* \author Markus Wegmann
*
**/


struct OneTexelVertex {
    float4 Position	: POSITION;
    float2 UV		: TEXCOORD0;
};

//// Vertex Shader ////

OneTexelVertex ScreenQuadVS(
		float3 Position : POSITION, 
		float2 UV	: TEXCOORD0
) {
    OneTexelVertex OUT = (OneTexelVertex)0;
    OUT.Position = float4(Position, 1);
    OUT.UV = float2(UV.xy);
    return OUT;
}

//// Fragment Shader ////

void godrays_blur(
        OneTexelVertex IN,
		
        out float4 oColor: COLOR,
        
        uniform float2 projSunLightPosition,
        uniform float exposure, 
        uniform float decay,
        uniform float density,
        uniform sampler2D decal)

{
	const int NUM_SAMPLES = 35;
	
	float2 texCoord = IN.UV;
	
	
	oColor = float4(0,0,0,1);
	
    float2 deltaTextCoord = IN.UV - projSunLightPosition;
    deltaTextCoord *= 1.0f / NUM_SAMPLES * density;

	float illuminationDecay = 1.0f;

    for(int i=0; i < NUM_SAMPLES; i++)
    {
        texCoord -= deltaTextCoord;
        float4 sample = tex2D(decal, texCoord);
		
		oColor += sample;
        sample *= illuminationDecay;

        illuminationDecay *= decay;
    }

    oColor *= exposure / NUM_SAMPLES;
}


void godrays_combine(
	OneTexelVertex IN,

    out float4 color : COLOR,

    uniform sampler2D renderDecal,
    uniform sampler2D godraysDecal)
{
    color = tex2D(renderDecal, IN.UV) + tex2D(godraysDecal, IN.UV);
}




/* CgFx based code

//// Variables ////
/////////////////////////////////////////////////////////////////////////////////////

float Script : STANDARDSGLOBAL <
    string UIWidget = "none";
    string ScriptClass = "scene";
    string ScriptOrder = "postprocess";
    string ScriptOutput = "color";
    string Script = "Technique=Main;";
> = 0.8;

float2 ProjSunLightPosition : Position <
    string UIName =  "Sun Light Position";
    string Space = "World";
> = {0, 0};

float4 SkyColor <
    string UIName =  "Sky Color";
	string UIWidget = "Color";
> = {0f,0f,0f,1.0f};

float GodraysExposure = 1f;
float GodraysDecay = 0.1f;
float GodraysDensity = 0.7f;

texture ScnTarget : RenderColorTarget <
	float2 ViewPortRatio = {1,1};
    int MipLevels = 1;
    string Format = "X8R8G8B8" ;
    string UIWidget = "None";
>;

sampler2D ScnDecal = sampler_state {
    Texture = <ScnTarget>;
	WrapS = Repeat;
    WrapT = Repeat;
    MinFilter = Linear;
    MagFilter = Linear;
};

texture GodraysTarget : RenderColorTarget <
	float2 ViewPortRatio = {1,1};
    int MipLevels = 1;
    string Format = "X8R8G8B8" ;
    string UIWidget = "None";
>;

sampler2D GodraysDecal = sampler_state {
    Texture = <GodraysTarget>;
	WrapS = ClampToEdge;
    WrapT = ClampToEdge;
    MinFilter = Linear;
    MagFilter = Linear;
};

texture DepthBuffer : RENDERDEPTHSTENCILTARGET <
    float2 ViewPortRatio = {1,1};
    string Format = "D24S8";
    string UIWidget = "None";
>;

texture LowDepthBuffer : RENDERDEPTHSTENCILTARGET <
    float2 ViewPortRatio = {1,1};
    string Format = "D24S8";
    string UIWidget = "None";
>;
//// UN-TWEAKABLES - AUTOMATICALLY-TRACKED TRANSFORMS ////////////////

float4x4 WorldITXf : WorldInverseTranspose < string UIWidget="None"; >;
float4x4 WvpXf : WorldViewProjection < string UIWidget="None"; >;
float4x4 VpXf : ViewProjection < string UIWidget="None"; >;
float4x4 WorldXf : World < string UIWidget="None"; >;
float4x4 ViewIXf : ViewInverse < string UIWidget="None"; >;

// Standard full-screen imaging value

float ClearDepth <
    string UIWidget = "None";
> = 1.0;

technique Main <
	string Script =
	"RenderColorTarget0=ScnTarget;"
	"RenderDepthStencilTarget=DepthBuffer;"
		"ClearSetColor=SkyColor;"
		"ClearSetDepth=ClearDepth;"
		"Clear=Color;"
		"Clear=Depth;"
	    "ScriptExternal=color;"
	"Pass=BlurRaw;"
	"Pass=CombineRender;";
>
{

	pass BlurRaw
	<
		string Script = "RenderColorTarget=GodrayTarget;"
			"RenderDepthStencilTarget=LowDepthBuffer;"
			"Draw=Buffer;";
    >
	{
		DepthTestEnable = false;
		DepthMask = false;
		BlendEnable = false;
		
		VertexShader = compile vp40 ScreenQuadVS();
    	FragmentProgram = compile fp40 godrays_blur(
            ProjSunLightPosition,
			GodraysExposure, 
			GodraysDecay, 
			GodraysDensity,
			ScnDecal);
  	}
	
	pass CombineRender
	<
		string Script = "RenderColorTarget0=;"
			"RenderDepthStencilTarget=;"
			"Draw=Buffer;";
    >
	{
		DepthTestEnable = false;
		DepthMask = false;
		BlendEnable = false;
		
		VertexShader = compile vp40 ScreenQuadVS();
    	FragmentProgram = compile fp40 godrays_combine(
			ScnDecal,
			GodraysDecal);
  	}
}

*/