uniform float4x4 ViewProj;
uniform texture2d image;
uniform float multiplier;

sampler_state def_sampler
{
  Filter   = Linear;
  AddressU = Clamp;
  AddressV = Clamp;
};

struct VertData
{
  float4 pos : POSITION;
  float2 uv  : TEXCOORD0;
};

VertData VSDefault(VertData vert_in)
{
  VertData vert_out;
  vert_out.pos = mul(float4(vert_in.pos.xyz, 1.0), ViewProj);
  vert_out.uv  = vert_in.uv;
  return vert_out;
}

float srgbToLinearChannel(float value)
{
  return value <= 0.04045 ? value / 12.92 :
    pow((value + 0.055) / 1.055, 2.4);
}

float3 srgbToLinear(float3 color)
{
  return float3(
    srgbToLinearChannel(color.r),
    srgbToLinearChannel(color.g),
    srgbToLinearChannel(color.b));
}

float4 PSCursor(VertData vert_in) : TARGET
{
  float4 pixel = image.Sample(def_sampler, vert_in.uv);

  if (pixel.a > 0.0)
  {
    /* Cursor RGB is premultiplied in nonlinear sRGB. Recover the straight
     * color before decoding it, then premultiply again in linear light. */
    float3 srgb = clamp(pixel.rgb / pixel.a, 0.0, 1.0);
    pixel.rgb = srgbToLinear(srgb) * pixel.a * multiplier;
  }
  else
    pixel.rgb = float3(0.0, 0.0, 0.0);

  return pixel;
}

technique Draw
{
  pass
  {
    vertex_shader = VSDefault(vert_in);
    pixel_shader  = PSCursor(vert_in);
  }
}