//note, 128.0 is the size of the texture width, hardcoded for now, needs to change
//to uniform variable.
void bilerp(in vec2 coords, out vec4 qtynew, in sampler2D qty)
{
  //figure out the texture coords
  vec4 st;
  st.xy = coords-1.0/128.0; //implied translation into texture simulation domain.
  st.zw = st.xy + 1.0/128.0; //top right corner of the "neighbor hood"
 
  //now access the texture
  vec4 t11 = texture2D(qty,st.xy);
  vec4 t21 = texture2D(qty,st.zy);
  vec4 t12 = texture2D(qty,st.xw);
  vec4 t22 = texture2D(qty,st.zw);
  //now lerp
  
  vec2 factor = (coords - st.xy)*128.0; //Factor is in simulation domain!
  //bilerp, such that, we compute lerp:
  //l1 = 11 to 21, l2 = 12 to 22, lerping long the x axis.
  //final = l1 to l2, lerping along the y axis. Please refer to any documentation on bilerp.
  qtynew = mix(mix(t11,t21,factor.x),mix(t12,t22,factor.x),factor.y);
}

float4 f4texRECTbilerp(samplerRECT tex, float2 s)

{

  float4 st;

  st.xy = floor(s - 0.5) + 0.5;

  st.zw = st.xy + 1;

  

  float2 t = s - st.xy; //interpolating factors 

    

  float4 tex11 = f4texRECT(tex, st.xy);

  float4 tex21 = f4texRECT(tex, st.zy);

  float4 tex12 = f4texRECT(tex, st.xw);

  float4 tex22 = f4texRECT(tex, st.zw);



  // bilinear interpolation

  return lerp(lerp(tex11, tex21, t.x), lerp(tex12, tex22, t.x), t.y);

}