title: Strange texture wrapping problem (fragment shader)
body: <p>I have this code (from Shadertoy):</p>
  <pre><code>void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
      vec2 uv = (fragCoord - 0.5*iResolution.xy) / iResolution.y; 
      fragColor = texture(iChannel0, vec2(atan(uv.y, uv.x)/6.28, 0.1/length(uv))); 
  }
  </code></pre>
  <p>...which creates an horizontal line glitch.
  <a href="https://i.stack.imgur.com/3gvCe.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3gvCe.jpg" alt="enter image description here" /></a></p>
  <p>If I slightly transform the first line :</p>
  <pre><code>void mainImage( out vec4 fragColor, in vec2 fragCoord ) {
      vec2 uv = fragCoord / iResolution.xy;
      uv -= 0.5;
      uv.x *= iResolution.x / iResolution.y;
      
      fragColor = texture(iChannel0, vec2(atan(uv.y, uv.x)/6.28, 0.1/length(uv))); 
  }
  </code></pre>
  <p>...no more problem.
  <a href="https://i.stack.imgur.com/AFhtg.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AFhtg.jpg" alt="enter image description here" /></a></p>
  <p>I don't even know where to start to understand what is happening !</p>