Distorted Android

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// Let d be the degree of the current vertex V with respect to center of the effect S and Region vRegion.

// This effect rotates the current vertex V by vInterpolated.x radians clockwise around the circle dilated

// by (1-d) around the center of the effect S.

  public static void enable()

    {

    addEffect(EffectName.SWIRL,

        "vec2 center  = vUniforms[effect+1].yz; \n"

      + "vec2 PS = center-v.xy; \n"

      + "vec4 SO = vUniforms[effect+2]; \n"

      + "float d1_circle = degree_region(SO,PS); \n"

      + "float d1_bitmap = degree_bitmap(center,PS); \n"

      + "float alpha = vUniforms[effect].x; \n"

      + "float sinA = sin(alpha); \n"

      + "float cosA = cos(alpha); \n"

      + "vec2 PS2 = vec2( PS.x*cosA+PS.y*sinA,-PS.x*sinA+PS.y*cosA ); \n" // vector PS rotated by A radians clockwise around center.

      + "vec4 SG = (1.0-d1_circle)*SO; \n"                                // coordinates of the dilated circle P is going to get rotated around

      + "float d2 = max(0.0,degree(SG,center,PS2)); \n"                   // make it a max(0,deg) because otherwise when center=left edge of the

                                                                          // bitmap some points end up with d2<0 and they disappear off view.

      + "v.xy += min(d1_circle,d1_bitmap)*(PS - PS2/(1.0-d2)); \n"        // if d2=1 (i.e P=center) we should have P unchanged. How to do it?

      );

    }