Android "Shader Editor" Application GLSL Camera Shader code [Inverted Edge]

gistfile1.txt

#extension GL_OES_standard_derivatives : enable

precision mediump float;

uniform vec2 resolution;
uniform vec2 cameraAddent;
uniform mat2 cameraOrientation;
uniform samplerExternalOES cameraBack;

void main(void) {
  vec2 uv = gl_FragCoord.xy / resolution.xy;
  vec2 st = cameraAddent + uv * cameraOrientation;
  vec3 color = texture2D(cameraBack, st).rgb;
  gl_FragColor = vec4(color, 1.0);

  float gray = length(color.rgb);
  gl_FragColor = vec4(vec3(step(0.06, length(vec2(dFdx(gray), dFdy(gray))))), 1.0);
  // Inverts it
  gl_FragColor = 1.0 - gl_FragColor;

}