//Application fed data
const float4x4 matWorldViewProj;


texture Sand_BM_bmap, Grass_BM_bmap, Rock_BM_bmap, Snow_BM_bmap;

// ColorMap Samplers
sampler SandSampler  = sampler_state  { Texture = <Sand_BM_bmap>;  };
sampler GrassSampler = sampler_state  { Texture = <Grass_BM_bmap>; };
sampler RockSampler  = sampler_state  { Texture = <Rock_BM_bmap>;  };
sampler SnowSampler  = sampler_state  { Texture = <Snow_BM_bmap>;  };




#define cMult 0.0001002707309736288
#define aSubtract 0.2727272727272727

float random(float4 t)
{ 
	float a, b, c, d;
	a=t.x+t.z*cMult+aSubtract-floor(t.x); 
	a*=a; 	b=t.y+a; 	b-=floor(b); 
	c=t.z+b; 	c-=floor(c); 	d=c; 
	a+=c*cMult+aSubtract-floor(a); 
	a*=a; b+=a;		b-=floor(b); 
	c+=b; c-=floor(c); 
	return ((a+b+c+d)/4); 
}


// Vertex Shader: 
void TerrPaintVS( in  float4 InPos:  POSITION,	in  float2 InTex: TEXCOORD0, 
						out float4 OutPos: POSITION,	out float2 OutTex: TEXCOORD0, 
						out float  Height: TEXCOORD1 											)	 
{ 
	// Transform the vertex from object space to projected world space: 
	OutPos = mul(InPos, 	matWorldViewProj);
	// Pass the texture coordinate to the pixel shader: 
	OutTex = InTex; 
	// Capture the Height of this vertex from object space... SEEMINGLY
	Height = InPos.y;
	// OPTIONALLY add some randomness to the demarkation line
	Height += (random(InPos)*30)-10;
}


// Pixel Shader: 
float4 TerrPaintPS(	in float4 InPos: POSITION,	 in float2 InTex: TEXCOORD0,
							in float  Height:TEXCOORD1											): COLOR 
{
	float4 Color = 0;

	if(Height < 32) Color = tex2D(SandSampler, InTex); 
	else if(Height < 42) Color = lerp(tex2D(SandSampler,InTex), tex2D(GrassSampler,InTex), (Height-32)/10);
	else if(Height < 75) Color = tex2D(GrassSampler, InTex); 
	else if(Height < 85) Color = lerp(tex2D(GrassSampler,InTex), tex2D(RockSampler,InTex), (Height-75)/10);
	else if(Height < 120) Color = tex2D(RockSampler, InTex); 
	else if(Height < 130) Color = lerp(tex2D(RockSampler,InTex), tex2D(SnowSampler,InTex), (Height-120)/10);
	else Color = tex2D(SnowSampler, InTex);

	return Color; 
} 



// Technique: 
technique AmbientTechnique 
{ 
	pass P0 
	{ 
		VertexShader = compile vs_2_0 TerrPaintVS(); 
		PixelShader  = compile ps_2_0 TerrPaintPS(); 
	} 
}