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      1 precision mediump float;
      2 
      3 // The actual wallpaper texture.
      4 uniform sampler2D uTexture;
      5 
      6 // The 85th percenile for the luminance histogram of the image (a value between 0 and 1).
      7 // This value represents the point in histogram that includes 85% of the pixels of the image.
      8 uniform float uPer85;
      9 
     10 // Reveal is the animation value that goes from 1 (the image is hidden) to 0 (the image is visible).
     11 uniform float uReveal;
     12 
     13 // The opacity of locked screen (constant value).
     14 uniform float uAod2Opacity;
     15 varying vec2 vTextureCoordinates;
     16 
     17 /*
     18  * Calculates the relative luminance of the pixel.
     19  */
     20 vec3 luminosity(vec3 color) {
     21     float lum = 0.2126 * color.r + 0.7152 * color.g + 0.0722 * color.b;
     22     return vec3(lum);
     23 }
     24 
     25 vec4 transform(vec3 diffuse) {
     26     // Getting the luminance for this pixel
     27     vec3 lum = luminosity(diffuse);
     28 
     29     /*
     30      * while the reveal > per85, it shows the luminance image (B&W image)
     31      * then when moving passed that value, the image gets colored.
     32      */
     33     float trans = smoothstep(0., uPer85, uReveal);
     34     diffuse = mix(diffuse, lum, trans);
     35 
     36     // 'lower' value represents the capped 'reveal' value to the range [0, per85]
     37     float selector = step(uPer85, uReveal);
     38     float lower = mix(uReveal, uPer85, selector);
     39 
     40     /*
     41      * Remaps image:
     42      * - from reveal=1 to reveal=per85 => lower=per85, diffuse=luminance
     43      *   That means that remaps black and white image pixel
     44      *   from a possible values of [0,1] to [per85, 1] (if the pixel is darker than per85,
     45      *   it's gonna be black, if it's between per85 and 1, it's gonna be gray
     46      *   and if it's 1 it's gonna be white).
     47      * - from reveal=per85 to reveal=0 => lower=reveal, 'diffuse' changes from luminance to color
     48      *   That means that remaps each image pixel color (rgb)
     49      *   from a possible values of [0,1] to [lower, 1] (if the pixel color is darker than 'lower',
     50      *   it's gonna be 0, if it's between 'lower' and 1, it's gonna be remap to a value
     51      *   between 0 and 1 and if it's 1 it's gonna be 1).
     52      * - if reveal=0 => lower=0, diffuse=color image
     53      *   The image is shown as it is, colored.
     54      */
     55     vec3 remaps = smoothstep(lower, 1., diffuse);
     56 
     57     // Interpolate between diffuse and remaps using reveal to avoid over saturation.
     58     diffuse = mix(diffuse, remaps, uReveal);
     59 
     60     /*
     61      * Fades in the pixel value:
     62      * - if reveal=1 => fadeInOpacity=0
     63      * - from reveal=1 to reveal=per85 => 0<=fadeInOpacity<=1
     64      * - if reveal>per85 => fadeInOpacity=1
     65      */
     66     float fadeInOpacity = 1. - smoothstep(uPer85, 1., uReveal);
     67     diffuse *= uAod2Opacity * fadeInOpacity;
     68 
     69     return vec4(diffuse.r, diffuse.g, diffuse.b, 1.);
     70 }
     71 
     72 void main() {
     73     // gets the pixel value of the wallpaper for this uv coordinates on screen.
     74     vec4 fragColor = texture2D(uTexture, vTextureCoordinates);
     75     gl_FragColor = transform(fragColor.rgb);
     76 }