Add Triangles logo animation texture and shader (#105)

Co-authored-by: Sebastian Krajewski <mail@wieku.me>
Co-authored-by: Dean Herbert <pe@ppy.sh>

osu.Game.Resources/Shaders/sh_HueAnimation.fs

@@ -0,0 +1,28 @@
+#include "sh_Utils.h"
+
+varying mediump vec2 v_TexCoord;
+varying lowp vec4 v_Colour;
+
+uniform lowp sampler2D m_Sampler;
+uniform lowp float progress;
+
+// Taken from http://lolengine.net/blog/2013/07/27/rgb-to-hsv-in-glsl
+vec3 rgb2hsv(vec3 c)
+{
+    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+    vec4 p = c.g < c.b ? vec4(c.bg, K.wz) : vec4(c.gb, K.xy);
+    vec4 q = c.r < p.x ? vec4(p.xyw, c.r) : vec4(c.r, p.yzx);
+
+    float d = q.x - min(q.w, q.y);
+    float e = 1.0e-10;
+    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
+}
+
+void main(void) 
+{
+    vec4 colour = toSRGB(texture2D(m_Sampler, v_TexCoord, -0.9));
+
+    vec3 hsv = rgb2hsv(colour.rgb);
+
+    gl_FragColor = hsv.x < progress ? toSRGB(vec4(v_Colour.rgb, v_Colour.a * colour.a * hsv.z)) : vec4(0);
+}