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diff --git a/slideshow/opengl/vortexVertexShader.glsl b/slideshow/opengl/vortexVertexShader.glsl
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+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#version 150
+
+#define M_PI 3.1415926535897932384626433832795
+
+in vec3 a_position;
+in vec3 a_normal;
+in vec2 a_texCoord;
+in float tileInfo;
+
+uniform mat4 u_modelViewMatrix;
+uniform mat4 u_sceneTransformMatrix;
+uniform mat4 u_primitiveTransformMatrix;
+uniform mat4 u_operationsTransformMatrix;
+
+uniform float time;
+uniform ivec2 numTiles;
+uniform sampler2D permTexture;
+uniform float slide;
+
+// Workaround for Intel's Windows driver, to prevent optimisation breakage.
+uniform float zero;
+
+out vec2 g_texturePosition;
+out vec3 g_normal;
+out mat4 modelViewMatrix;
+out mat4 transform;
+out float nTime;
+out float startTime;
+out float endTime;
+
+float snoise(vec2 p)
+{
+ return texture(permTexture, p).r;
+}
+
+mat4 identityMatrix(void)
+{
+ return mat4(1.0, 0.0, 0.0, 0.0,
+ 0.0, 1.0, 0.0, 0.0,
+ 0.0, 0.0, 1.0, 0.0,
+ 0.0, 0.0, 0.0, 1.0);
+}
+
+mat4 translationMatrix(vec3 axis)
+{
+ mat4 matrix = identityMatrix();
+ matrix[3] = vec4(axis, 1.0);
+ return matrix;
+}
+
+mat4 rotationMatrix(vec3 axis, float angle)
+{
+ axis = normalize(axis);
+ float s = sin(angle);
+ float c = cos(angle);
+ float oc = 1.0 - c;
+
+ return mat4(oc * axis.x * axis.x + c, oc * axis.x * axis.y - axis.z * s, oc * axis.z * axis.x + axis.y * s, 0.0,
+ oc * axis.x * axis.y + axis.z * s, oc * axis.y * axis.y + c, oc * axis.y * axis.z - axis.x * s, 0.0,
+ oc * axis.z * axis.x - axis.y * s, oc * axis.y * axis.z + axis.x * s, oc * axis.z * axis.z + c, 0.0,
+ 0.0, 0.0, 0.0, 1.0);
+}
+
+void main( void )
+{
+ // Each tile moves during only half of the transition. The leftmost
+ // tiles start moving at the start and arrive at their end
+ // position around time=0.5, when the tiles there (the rightmost
+ // ones) start moving. (The exact time each tile is moving is
+ // fuzzed a bit to make a more random appearance.)
+
+ // In GLSL 1.20 we don't have any bitwise operators, sigh
+
+ int tileXIndex = int(mod(int(tileInfo), 256));
+ int tileYIndex = int(mod(int(tileInfo) / 256, 256));
+
+ // A semi-random number 0..1, different for neighbouring tiles, to know when they should start moving.
+ float startTimeFuzz = snoise(vec2(float(tileXIndex)/(numTiles.x-1), float(tileYIndex)/(numTiles.y-1)));
+
+ // A semi-random number -1.5..1.5, different for neighbouring tiles, to specify their rotation center.
+ // The additional 0.5 on each side is because we want some tiles to rotate outside.
+ float rotationFuzz = snoise(vec2(float(numTiles.x + tileXIndex)/(numTiles.x-1), float(tileYIndex)/(numTiles.y-1))) * 3.0 - 1.5;
+
+ startTime = float(tileXIndex)/(numTiles.x-1) * 0.2 + startTimeFuzz * 0.2;
+ endTime = min(startTime + 0.7, 1.0);
+
+ bool isLeavingSlide = (slide < 0.5);
+ const vec4 invalidPosition = vec4(-256.0, -256.0, -256.0, -256.0);
+
+ // Don’t display the tile before or after its rotation, depending on the slide.
+ if (!isLeavingSlide)
+ {
+ if (time < max(0.3, startTime))
+ {
+ gl_Position = invalidPosition;
+ return;
+ }
+ nTime = 1.0 - time;
+ }
+ else
+ {
+ if (time > endTime)
+ {
+ gl_Position = invalidPosition;
+ return;
+ }
+ nTime = time;
+ }
+
+ transform = identityMatrix();
+ if (nTime > startTime && nTime <= endTime)
+ {
+ // We are in the rotation part.
+ float rotation = (nTime - startTime) / (endTime - startTime);
+ if (isLeavingSlide)
+ rotation *= -1.0;
+
+ if (rotation < -0.5 || rotation > 0.5) {
+ gl_Position = invalidPosition;
+ return;
+ }
+
+ // Translation vector to set the origin of the rotation.
+ vec3 translationVector = vec3(rotationFuzz, 0.0, 0.0);
+
+ // Compute the actual rotation matrix.
+
+ // Intel's Windows driver gives a wrong matrix when all operations are done at once.
+ if (zero < 1.0)
+ transform = translationMatrix(translationVector) * transform;
+ if (zero < 2.0)
+ transform = rotationMatrix(vec3(0.0, 1.0, 0.0), clamp(rotation, -1.0, 1.0) * M_PI) * transform;
+ if (zero < 3.0)
+ transform = translationMatrix(-translationVector) * transform;
+ }
+
+ modelViewMatrix = u_modelViewMatrix * u_operationsTransformMatrix * u_sceneTransformMatrix * u_primitiveTransformMatrix;
+ gl_Position = vec4(a_position, 1.0);
+
+ g_texturePosition = a_texCoord;
+ g_normal = a_normal;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */