Fixed anti aliasing shader

README.md

@@ -38,7 +38,7 @@ This example sets alpha to either `0` or `1`. Edges can also be anti aliased usi
 ``` glsl
 vec4 pixel = texture(source, uv);
 
-vec4 color = vec4(pixel.rgb, clamp(0.5 - pixel.a * 2.0 / fwidth(pixel.a), 0., 1.)));
+vec4 color = vec4(pixel.rgb, clamp((pixel.a - 0.5) * 2.0 / fwidth(pixel.a), 0., 1.)));
 ```
 
 This example interpolates alpha from `0` to `1` using standard derivatives, creating smooth anti aliased edges.

js/gl/shaderPreview.js

@@ -31,7 +31,7 @@ export class ShaderPreview extends Shader {
                 mix(
                     vec3(0.),
                     pixel.rgb,
-                    clamp(.5 - pixel.a * 2. / fwidth(pixel.a), 0., 1.)),
+                    clamp((pixel.a - .5) * 2. / fwidth(pixel.a), 0., 1.)),
                 1. - clamp((length(delta) - radius) * radiusPixels, 0., 1.));
         }
     `;