// Camera Parameters
float4x4 View;
float4x4 Projection;

// Particle texture and sampler.
texture Texture;

sampler Sampler = sampler_state
{
    Texture = (Texture);
    
    MinFilter = Linear;
    MagFilter = Linear;
    MipFilter = Point;
    
    AddressU = Clamp;
    AddressV = Clamp;
};

// Vertex shader input structure specifies the position, size, and
// color of the particle, plus a 2x2 rotation matrix (packed into
// a float4 value because we don't have enough color interpolators
// to send this directly as a float2x2).
struct VertexShaderInput
{
    float3 Position : POSITION0;
    float2 Size : PSIZE0;
    float4 Color : COLOR0;
};

// Vertex shader output structure specifies the position, size, and
// color of the particle, plus a 2x2 rotation matrix (packed into
// a float4 value because we don't have enough color interpolators
// to send this directly as a float2x2).
struct VertexShaderOutput
{
    float4 Position : POSITION0;
    float Size : PSIZE0;
    float4 Color : COLOR0;
};

// Custom vertex shader animates particles entirely on the GPU.
VertexShaderOutput VertexShader(VertexShaderInput input)
{
    VertexShaderOutput output;
    
    // Compute the particle position, size, color, and rotation.
    output.Position = mul(mul(float4(input.Position, 1), View), Projection);
    
    float size = lerp(input.Size.x, input.Size.y, (input.Size.x + input.Size.y)/2);

    if (output.Position.z <= 1) 
    {
		output.Size = size;
    }
    else
    {
		output.Size = size * sqrt(1 / output.Position.z);
    }

    output.Color = input.Color;
    
    return output;
}

// Pixel shader input structure for particles that do not rotate.
struct NonRotatingPixelShaderInput
{
    float4 Color : COLOR0;
    
#ifdef XBOX
    float2 TextureCoordinate : SPRITETEXCOORD;
#else
    float2 TextureCoordinate : TEXCOORD0;
#endif
};


// Pixel shader for drawing particles that do not rotate.
float4 NonRotatingPixelShader(NonRotatingPixelShaderInput input) : COLOR0
{
    return tex2D(Sampler, input.TextureCoordinate) * input.Color;
}

technique Technique1
{
    pass Pass1
    {
        // TODO: set renderstates here.

        VertexShader = compile vs_1_1 VertexShader();
        PixelShader = compile ps_1_1 NonRotatingPixelShader();
    }
}