Hide visible scrolling in static noise

Randomize vertical position of staticNoise texel and add to
existing scrolling of noise texture (both horizontal and vertical;
faster in vertical direction)

app/qml/ShaderTerminal.qml

@@ -247,6 +247,17 @@ Item {
              "  return outColor;
              }" +
 
+             //pseudo-random vector
+             //https://stackoverflow.com/a/10625698
+             "float random( vec2 p )
+             {
+                 vec2 K1 = vec2(
+                     23.14069263277926, // e^pi (Gelfond's constant)
+                     2.665144142690225 // 2^sqrt(2) (Gelfond-Schneider constant)
+                 );
+                 return fract( cos( dot(p,K1) ) * 12345.6789 );
+             }" +
+
              "void main() {" +
                  "vec2 cc = vec2(0.5) - qt_TexCoord0;" +
                  "float distance = length(cc);" +
@@ -285,7 +296,11 @@ Item {
                  : "") +
 
                  (jitter !== 0 || staticNoise !== 0 ?
-                     "vec4 noiseTexel = texture2D(noiseSource, scaleNoiseSize * coords + vec2(fract(time / 51.0), fract(time / 237.0)));"
+                 "vec4 noiseTexel = texture2D(
+                     noiseSource, scaleNoiseSize * coords
+                     + vec2(0.0, random(vec2(fract(time / 237.0), 822.9582)))
+                     + vec2(fract(time / 31.0), fract(time / 177.0))
+                 );"
                  : "") +
 
                  (jitter !== 0 ? "

packaging/appdata/cool-retro-term.appdata.xml

@@ -16,11 +16,11 @@
   <screenshots>
     <screenshot type="default">
       <caption>Default amber look</caption>
-      <image width="1022" height="791">https://i.imgur.com/NUfvnlu.png</image>
+      <image width="1022" height="791">https://camo.githubusercontent.com/2443e662e95733ba6ae331f391f6ec036d1ee7fd/687474703a2f2f692e696d6775722e636f6d2f4e5566766e6c752e706e67</image>
     </screenshot>
     <screenshot>
       <caption>Apple II look</caption>
-      <image width="1024" height="796">https://i.imgur.com/MMmM6Ht.png</image>
+      <image width="1024" height="796">https://camo.githubusercontent.com/44a19842d532555c7b02bf6b4b4684add9edf18c/687474703a2f2f692e696d6775722e636f6d2f4d4d6d4d3648742e706e67</image>
     </screenshot>
   </screenshots>