texture2D vectorField;
sampler2D vectorSampler = sampler_state
{
	Texture = <vectorField>;
	MipFilter = POINT;
	MinFilter = POINT;
	MagFilter = POINT;
	AddressU = CLAMP;
	AddressV = CLAMP;		
};


struct vertexInput {
    float4 position		: POSITION;
};

struct vertexOutput {
    float4 position		: POSITION;
    float4 colour		: COLOR0;
};

//------------------------------------
float4x4 View : View;
float4x4 Projection : Projection;

float scale;
float4 pos;
float4 colour;

const float2 plusminus = float2(1,-1);

vertexOutput vsArrow(vertexInput IN) 
{
    vertexOutput OUT;
    float4 p = float4(0,0,0,1);
    float2 vect = tex2Dlod(vectorSampler, pos).xy;
  
    p.x = dot(IN.position.xy, vect*plusminus);
    p.y = dot(IN.position.xy, vect.yx);
    p *= scale;
    
    pos.xy = (pos.xy-float2(0.5,0.5))*plusminus;
    OUT.position = mul( p+pos, View);
    OUT.position = mul( OUT.position, Projection);
    OUT.colour = colour;

    return OUT;
}