#ifdef GL_ES

precision mediump float;

#endif

uniform mat3 worldToOutput;

uniform vec4 outputRect;

varying vec4 inputRect[1];

varying mat3 worldToInput[1];

uniform vec2  center;

uniform float radius;

uniform float blur;

float det(mat3 m) { return m[0][0] * m[1][1] - m[0][1] * m[1][0]; }

float scale     = sqrt(abs(det(worldToOutput)));

vec2  center_   = (worldToOutput * vec3(center, 1.0)).xy;

float rad_      = scale * max(radius, 0.0);

void addPoint(inout vec4 rect, vec2 p) {

  rect.xy = min(rect.xy, p);

  rect.zw = max(rect.zw, p);

}

void addBlurredPointBox(inout vec4 rect, vec2 p)

{

  vec2 v        = p - center_;

  float vLength = length(v);

  float dist    = max(length(v) - rad_, 0.0);

  float b       = blur * dist;

  v *= (b / max(vLength, 0.01));

  addPoint(rect, p - v);

  addPoint(rect, p + v);

}

void main( void )

{

  worldToInput[0] = worldToOutput;                    // Let the input and output references be the same

  inputRect[0]    = outputRect;

  // Add the bounding box of each blurred corner

  addBlurredPointBox(inputRect[0], outputRect.xy);

  addBlurredPointBox(inputRect[0], outputRect.xw);

  addBlurredPointBox(inputRect[0], outputRect.zy);

  addBlurredPointBox(inputRect[0], outputRect.zw);

  gl_Position = vec4(0.0);                            // Does not link without

}