<img id="tiles" src="tiles.jpg">
<img id="xneg" src="xneg.jpg">
<img id="xpos" src="xpos.jpg">
<img id="ypos" src="ypos.jpg">
<img id="zneg" src="zneg.jpg">
<img id="zpos" src="zpos.jpg">

function Water() {
 var vertexShader = '\
 varying vec2 coord;\
 void main() {\
 coord = gl_Vertex.xy * 0.5 + 0.5;\
 gl_Position = vec4(gl_Vertex.xyz, 1.0);\
 }\
 ';
 this.plane = GL.Mesh.plane();
 if (!GL.Texture.canUseFloatingPointTextures()) {
 throw new Error('This demo requires the OES_texture_float extension');
 }
 var filter = GL.Texture.canUseFloatingPointLinearFiltering() ? gl.LINEAR : gl.NEAREST;
 this.textureA = new GL.Texture(256, 256, { type: gl.FLOAT, filter: filter });
 this.textureB = new GL.Texture(256, 256, { type: gl.FLOAT, filter: filter });
 this.dropShader = new GL.Shader(vertexShader, '\
 const float PI = 3.141592653589793;\
 uniform sampler2D texture;\
 uniform vec2 center;\
 uniform float radius;\
 uniform float strength;\
 varying vec2 coord;\
 void main() {\
 /* get vertex info */\
 vec4 info = texture2D(texture, coord);\
 \
 /* add the drop to the height */\
 float drop = max(0.0, 1.0 - length(center * 0.5 + 0.5 - coord) / radius);\
 drop = 0.5 - cos(drop * PI) * 0.5;\
 info.r += drop * strength;\
 \
 gl_FragColor = info;\
 }\
 ');
 this.updateShader = new GL.Shader(vertexShader, '\
 uniform sampler2D texture;\
 uniform vec2 delta;\
 varying vec2 coord;\
 void main() {\
 /* get vertex info */\
 vec4 info = texture2D(texture, coord);\
 \
 /* calculate average neighbor height */\
 vec2 dx = vec2(delta.x, 0.0);\
 vec2 dy = vec2(0.0, delta.y);\
 float average = (\
 texture2D(texture, coord - dx).r +\
 texture2D(texture, coord - dy).r +\
 texture2D(texture, coord + dx).r +\
 texture2D(texture, coord + dy).r\
 ) * 0.25;\
 \
 /* change the velocity to move toward the average */\
 info.g += (average - info.r) * 2.0;\
 \
 /* attenuate the velocity a little so waves do not last forever */\
 info.g *= 0.995;\
 \
 /* move the vertex along the velocity */\
 info.r += info.g;\
 \
 gl_FragColor = info;\
 }\
 ');
 this.normalShader = new GL.Shader(vertexShader, '\
 uniform sampler2D texture;\
 uniform vec2 delta;\
 varying vec2 coord;\
 void main() {\
 /* get vertex info */\
 vec4 info = texture2D(texture, coord);\
 \
 /* update the normal */\
 vec3 dx = vec3(delta.x, texture2D(texture, vec2(coord.x + delta.x, coord.y)).r - info.r, 0.0);\
 vec3 dy = vec3(0.0, texture2D(texture, vec2(coord.x, coord.y + delta.y)).r - info.r, delta.y);\
 info.ba = normalize(cross(dy, dx)).xz;\
 \
 gl_FragColor = info;\
 }\
 ');
 this.sphereShader = new GL.Shader(vertexShader, '\
 uniform sampler2D texture;\
 uniform vec3 oldCenter;\
 uniform vec3 newCenter;\
 uniform float radius;\
 varying vec2 coord;\
 \
 float volumeInSphere(vec3 center) {\
 vec3 toCenter = vec3(coord.x * 2.0 - 1.0, 0.0, coord.y * 2.0 - 1.0) - center;\
 float t = length(toCenter) / radius;\
 float dy = exp(-pow(t * 1.5, 6.0));\
 float ymin = min(0.0, center.y - dy);\
 float ymax = min(max(0.0, center.y + dy), ymin + 2.0 * dy);\
 return (ymax - ymin) * 0.1;\
 }\
 \
 void main() {\
 /* get vertex info */\
 vec4 info = texture2D(texture, coord);\
 \
 /* add the old volume */\
 info.r += volumeInSphere(oldCenter);\
 \
 /* subtract the new volume */\
 info.r -= volumeInSphere(newCenter);\
 \
 gl_FragColor = info;\
 }\
 ');
}

Water.prototype.addDrop = function(x, y, radius, strength) {
 var this_ = this;
 this.textureB.drawTo(function() {
 this_.textureA.bind();
 this_.dropShader.uniforms({
 center: [x, y],
 radius: radius,
 strength: strength
 }).draw(this_.plane);
 });
 this.textureB.swapWith(this.textureA);
};

Water.prototype.moveSphere = function(oldCenter, newCenter, radius) {
 var this_ = this;
 this.textureB.drawTo(function() {
 this_.textureA.bind();
 this_.sphereShader.uniforms({
 oldCenter: oldCenter,
 newCenter: newCenter,
 radius: radius
 }).draw(this_.plane);
 });
 this.textureB.swapWith(this.textureA);
};

Water.prototype.stepSimulation = function() {
 var this_ = this;
 this.textureB.drawTo(function() {
 this_.textureA.bind();
 this_.updateShader.uniforms({
 delta: [1 / this_.textureA.width, 1 / this_.textureA.height]
 }).draw(this_.plane);
 });
 this.textureB.swapWith(this.textureA);
};

Water.prototype.updateNormals = function() {
 var this_ = this;
 this.textureB.drawTo(function() {
 this_.textureA.bind();
 this_.normalShader.uniforms({
 delta: [1 / this_.textureA.width, 1 / this_.textureA.height]
 }).draw(this_.plane);
 });
 this.textureB.swapWith(this.textureA);
};