slideshow: Improve the Ripple transition to match PowerPoint better

Change-Id: I0b8a78fc6bce5cb737cc7070b1b69184c5f6991c

1 files changed, 33 insertions, 11 deletions

diff --git a/slideshow/opengl/rippleFragmentShader.glsl b/slideshow/opengl/rippleFragmentShader.glsl
index ac6b8ac37099..ec641d67a571 100644
--- a/slideshow/opengl/rippleFragmentShader.glsl
+++ b/slideshow/opengl/rippleFragmentShader.glsl
@@ -15,21 +15,43 @@ uniform sampler2D leavingSlideTexture;
 uniform sampler2D enteringSlideTexture;
 uniform float time;
 uniform vec2 center;
+uniform float slideRatio;
+
 varying vec2 v_texturePosition;
 
+// This function returns the distance between two points, taking into account the slide ratio.
+float betterDistance(vec2 p1, vec2 p2)
+{
+    p1.x *= slideRatio;
+    p2.x *= slideRatio;
+    return distance(p1, p2);
+}
+
 void main()
 {
-    float d = length(v_texturePosition - center);
-    float w = 0;
-    w = max(w, length(center - vec2(0, 0)));
-    w = max(w, length(center - vec2(1, 0)));
-    w = max(w, length(center - vec2(1, 1)));
-    w = max(w, length(center - vec2(0, 1)));
-    float v = 0.2;
-    float smoothtime = smoothstep(0, 1, time);
-    float a = smoothstep(smoothtime*w-v, smoothtime*w+v, d);
-    a += (0.5 - abs(a-0.5))*sin(d*M_PI*30);
-    gl_FragColor = mix(texture2D(enteringSlideTexture, v_texturePosition), texture2D(leavingSlideTexture, v_texturePosition), a);
+    const float w = 0.5;
+    const float v = 0.1;
+
+    // Distance from this fragment to the center, in slide coordinates.
+    float dist = betterDistance(center, v_texturePosition);
+
+    // We want the ripple to span all of the slide at the end of the transition.
+    float t = time * (sqrt(2.0) * (slideRatio < 1.0 ? 1.0 / slideRatio : slideRatio));
+
+    // Interpolate the distance to the center in fonction of the time.
+    float mixed = smoothstep(t*w-v, t*w+v, dist);
+
+    // Get the displacement offset from the current pixel, for fragments that have been touched by the ripple already.
+    vec2 offset = (v_texturePosition - center) * (sin(dist * 64.0 - time * 16.0) + 0.5) / 32.0;
+    vec2 wavyTexCoord = mix(v_texturePosition + offset, v_texturePosition, time);
+
+    // Get the final position we will sample from.
+    vec2 pos = mix(wavyTexCoord, v_texturePosition, mixed);
+
+    // Sample from the textures and mix that together.
+    vec4 leaving = texture2D(leavingSlideTexture, pos);
+    vec4 entering = texture2D(enteringSlideTexture, pos);
+    gl_FragColor = mix(entering, leaving, mixed);
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */