Jinc shader with anti-ringing

/* COMPATIBILITY
   - HLSL compilers
   - Cg   compilers
*/

/*
   Hyllian's lanczos2-sharp Shader

   Copyright (C) 2011-2014 Hyllian/Jararaca - [email protected]

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/

    const static float     floatpi     = 1.5707963267948966192313216916398;
    const static float         pi     = 3.1415926535897932384626433832795;

// Calculates the distance between two points
float d(float2 pt1, float2 pt2)
{
  float2 v = pt2 - pt1;
  return sqrt(dot(v,v));
}

float3 min4(float3 a, float3 b, float3 c, float3 d)
{
    return min(a, min(b, min(c, d)));
}
float3 max4(float3 a, float3 b, float3 c, float3 d)
{
    return max(a, max(b, max(c, d)));
}


    struct input
    {
        float2 video_size;
        float2 texture_size;
        float2 output_size;
            float  frame_count;
            float  frame_direction;
        float frame_rotation;
    };


    struct out_vertex {
        float4 position : POSITION;
        float4 color    : COLOR;
        float2 texCoord : TEXCOORD0;
    };

    /*    VERTEX_SHADER    */
    out_vertex main_vertex
    (
        float4 position    : POSITION,
        float4 color    : COLOR,
        float2 texCoord1   : TEXCOORD0,

           uniform float4x4 modelViewProj,
        uniform input IN
    )
    {

	// This line fix a bug in ATI cards.
	float2 tex = texCoord1;

        out_vertex OUT = {
            mul(modelViewProj, position),
            color,
            tex
        };

        return OUT;
    }

    float4 lanczos(float4 x)
    {
      float4 res;
//    res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(pi*floatpi)  :  sin(x*floatpi)*sin(x*pi)/(x*x);

//    res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(1.0)  :  (2/(pi*pi))*sin(x*floatpi)*sin(x*pi)/(x*x);

//    res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(0.5)  :  pi*cos(x*pi)*pi*cos(x*pi*(1.22/2.233));

//      res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(0.5)  :  2*(0.5-x*x/16.0+x*x*x*x/384.0)*sin(pi*x)/(pi*x);

res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(1.0)  :  sin(pi*x*0.4)*sin(x*pi*0.825)/(0.4*0.825*pi*x*pi*x);

//res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(1.0)  :  cos(x)*sin(x*pi)/(pi*x);

//res = (x==float4(0.0, 0.0, 0.0, 0.0)) ?  float4(1.0)  :  cos(x/floatpi)*sin(x*pi)/(pi*x); // Unknown filter kernel


      return res;
    }

    float4 main_fragment(in out_vertex VAR, uniform sampler2D s_p : TEXUNIT0, uniform input IN) : COLOR
    {
      float3 color;
      float4x4 weights;

      float2 dx = float2(1.0, 0.0);
      float2 dy = float2(0.0, 1.0);

      float2 pc = VAR.texCoord*IN.texture_size;

      float2 tc = (floor(pc-float2(0.5,0.5))+float2(0.5,0.5));

      weights[0] = lanczos(float4(d(pc, tc    -dx    -dy), d(pc, tc           -dy), d(pc, tc    +dx    -dy), d(pc, tc+2.0*dx    -dy)));
      weights[1] = lanczos(float4(d(pc, tc    -dx       ), d(pc, tc              ), d(pc, tc    +dx       ), d(pc, tc+2.0*dx       )));
      weights[2] = lanczos(float4(d(pc, tc    -dx    +dy), d(pc, tc           +dy), d(pc, tc    +dx    +dy), d(pc, tc+2.0*dx    +dy)));
      weights[3] = lanczos(float4(d(pc, tc    -dx+2.0*dy), d(pc, tc       +2.0*dy), d(pc, tc    +dx+2.0*dy), d(pc, tc+2.0*dx+2.0*dy)));

//      weights[0].x = weights[0].w = weights[3].x = weights[3].w = 0.0;

      dx = dx/IN.texture_size;
      dy = dy/IN.texture_size;
      tc = tc/IN.texture_size;

    // reading the texels

      float3 c00 = tex2D(s_p, tc    -dx    -dy).xyz;
      float3 c10 = tex2D(s_p, tc           -dy).xyz;
      float3 c20 = tex2D(s_p, tc    +dx    -dy).xyz;
      float3 c30 = tex2D(s_p, tc+2.0*dx    -dy).xyz;
      float3 c01 = tex2D(s_p, tc    -dx       ).xyz;
      float3 c11 = tex2D(s_p, tc              ).xyz;
      float3 c21 = tex2D(s_p, tc    +dx       ).xyz;
      float3 c31 = tex2D(s_p, tc+2.0*dx       ).xyz;
      float3 c02 = tex2D(s_p, tc    -dx    +dy).xyz;
      float3 c12 = tex2D(s_p, tc           +dy).xyz;
      float3 c22 = tex2D(s_p, tc    +dx    +dy).xyz;
      float3 c32 = tex2D(s_p, tc+2.0*dx    +dy).xyz;
      float3 c03 = tex2D(s_p, tc    -dx+2.0*dy).xyz;
      float3 c13 = tex2D(s_p, tc       +2.0*dy).xyz;
      float3 c23 = tex2D(s_p, tc    +dx+2.0*dy).xyz;
      float3 c33 = tex2D(s_p, tc+2.0*dx+2.0*dy).xyz;

//      float3 min_sample = min(c11, min(min4(c00, c01, c02, c12), min4(c10, c20, c21, c22)));
//      float3 max_sample = max(c11, max(max4(c00, c01, c02, c12), max4(c10, c20, c21, c22)));

//      float3 min_sample = min(min4(c01, c10, c02, c20), min4(c11, c21, c12, c22));
//      float3 max_sample = max(max4(c01, c10, c02, c20), max4(c11, c21, c12, c22));

      //  Get min/max samples
      float3 min_sample = min4(c11, c21, c12, c22);
      float3 max_sample = max4(c11, c21, c12, c22);


//    float3 min_sample = min4(min4(c00, c01, c02, c03), min4(c10, c11, c12, c13), min4(c20, c21, c22, c23), min4(c30, c31, c32, c33));
//    float3 max_sample = max4(max4(c00, c01, c02, c03), max4(c10, c11, c12, c13), max4(c20, c21, c22, c23), max4(c30, c31, c32, c33));



      color = mul(weights[0], float4x3(c00, c10, c20, c30));
      color+= mul(weights[1], float4x3(c01, c11, c21, c31));
      color+= mul(weights[2], float4x3(c02, c12, c22, c32));
      color+= mul(weights[3], float4x3(c03, c13, c23, c33));
      color = color/(dot(mul(weights, float4(1)), 1));

      // Anti-ringing
      color = clamp(color, min_sample, max_sample);

      // final sum and weight normalization
      return float4(color, 1);

    }