clean up update shader; uncap particle speed at poles

dist/wind-gl.js

@@ -1,7 +1,7 @@
 (function (global, factory) {
-    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
-    typeof define === 'function' && define.amd ? define(factory) :
-    (global.WindGL = factory());
+	typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
+	typeof define === 'function' && define.amd ? define(factory) :
+	(global.WindGL = factory());
 }(this, (function () { 'use strict';
 
 function createShader(gl, type, source) {
@@ -95,7 +95,7 @@ var quadVert = "precision mediump float;\n\nattribute vec2 a_pos;\n\nvarying vec
 
 var screenFrag = "precision mediump float;\n\nuniform sampler2D u_screen;\nuniform float u_opacity;\n\nvarying vec2 v_tex_pos;\n\nvoid main() {\n    vec4 color = texture2D(u_screen, 1.0 - v_tex_pos);\n    // a hack to guarantee opacity fade out even with a value close to 1.0\n    gl_FragColor = vec4(floor(255.0 * color * u_opacity) / 255.0);\n}\n";
 
-var updateFrag = "precision highp float;\n\nuniform sampler2D u_particles;\nuniform sampler2D u_wind;\nuniform vec2 u_wind_res;\nuniform vec2 u_wind_min;\nuniform vec2 u_wind_max;\nuniform float u_rand_seed;\nuniform float u_speed_factor;\nuniform float u_drop_rate;\nuniform float u_drop_rate_bump;\n\nvarying vec2 v_tex_pos;\n\n// pseudo-random generator\nconst vec3 rand_constants = vec3(12.9898, 78.233, 4375.85453);\nfloat rand(const vec2 co) {\n    float t = dot(rand_constants.xy, co);\n    return fract(sin(t) * (rand_constants.z + t));\n}\n\n// wind speed lookup; use manual bilinear filtering based on 4 adjacent pixels for smooth interpolation\nvec2 lookup_wind(const vec2 uv) {\n    // return texture2D(u_wind, uv).rg; // lower-res hardware filtering\n    vec2 px = 1.0 / u_wind_res;\n    vec2 vc = (floor(uv * u_wind_res)) * px;\n    vec2 f = fract(uv * u_wind_res);\n    vec2 tl = texture2D(u_wind, vc).rg;\n    vec2 tr = texture2D(u_wind, vc + vec2(px.x, 0)).rg;\n    vec2 bl = texture2D(u_wind, vc + vec2(0, px.y)).rg;\n    vec2 br = texture2D(u_wind, vc + px).rg;\n    return mix(mix(tl, tr, f.x), mix(bl, br, f.x), f.y);\n}\n\nvoid main() {\n    vec4 color = texture2D(u_particles, v_tex_pos);\n    vec2 pos = vec2(\n        color.r / 255.0 + color.b,\n        color.g / 255.0 + color.a); // decode particle position from pixel RGBA\n\n    vec2 velocity = mix(u_wind_min, u_wind_max, lookup_wind(pos));\n    float speed_t = length(velocity) / length(u_wind_max);\n\n    // take EPSG:4236 distortion into account for calculating where the particle moved\n    float distortion = max(0.1, cos(radians(pos.y * 180.0 - 90.0)));\n    vec2 offset = vec2(velocity.x / distortion, -velocity.y) * 0.0001 * u_speed_factor;\n\n    // a random seed to use for the particle drop\n    vec2 seed = (pos + v_tex_pos) * u_rand_seed;\n\n    // drop rate is a chance a particle will restart at random position, to avoid degeneration\n    float dropRate = u_drop_rate + speed_t * u_drop_rate_bump;\n    float drop = step(1.0 - dropRate, rand(seed));\n    pos = mix(fract(1.0 + pos + offset), vec2(rand(seed + 1.3), rand(seed + 2.1)), drop);\n\n    // encode the new particle position back into RGBA\n    gl_FragColor = vec4(\n        fract(pos * 255.0),\n        floor(pos * 255.0) / 255.0);\n}\n";
+var updateFrag = "precision highp float;\n\nuniform sampler2D u_particles;\nuniform sampler2D u_wind;\nuniform vec2 u_wind_res;\nuniform vec2 u_wind_min;\nuniform vec2 u_wind_max;\nuniform float u_rand_seed;\nuniform float u_speed_factor;\nuniform float u_drop_rate;\nuniform float u_drop_rate_bump;\n\nvarying vec2 v_tex_pos;\n\n// pseudo-random generator\nconst vec3 rand_constants = vec3(12.9898, 78.233, 4375.85453);\nfloat rand(const vec2 co) {\n    float t = dot(rand_constants.xy, co);\n    return fract(sin(t) * (rand_constants.z + t));\n}\n\n// wind speed lookup; use manual bilinear filtering based on 4 adjacent pixels for smooth interpolation\nvec2 lookup_wind(const vec2 uv) {\n    // return texture2D(u_wind, uv).rg; // lower-res hardware filtering\n    vec2 px = 1.0 / u_wind_res;\n    vec2 vc = (floor(uv * u_wind_res)) * px;\n    vec2 f = fract(uv * u_wind_res);\n    vec2 tl = texture2D(u_wind, vc).rg;\n    vec2 tr = texture2D(u_wind, vc + vec2(px.x, 0)).rg;\n    vec2 bl = texture2D(u_wind, vc + vec2(0, px.y)).rg;\n    vec2 br = texture2D(u_wind, vc + px).rg;\n    return mix(mix(tl, tr, f.x), mix(bl, br, f.x), f.y);\n}\n\nvoid main() {\n    vec4 color = texture2D(u_particles, v_tex_pos);\n    vec2 pos = vec2(\n        color.r / 255.0 + color.b,\n        color.g / 255.0 + color.a); // decode particle position from pixel RGBA\n\n    vec2 velocity = mix(u_wind_min, u_wind_max, lookup_wind(pos));\n    float speed_t = length(velocity) / length(u_wind_max);\n\n    // take EPSG:4236 distortion into account for calculating where the particle moved\n    float distortion = cos(radians(pos.y * 180.0 - 90.0));\n    vec2 offset = vec2(velocity.x / distortion, -velocity.y) * 0.0001 * u_speed_factor;\n\n    // update particle position, wrapping around the date line\n    pos = fract(1.0 + pos + offset);\n\n    // a random seed to use for the particle drop\n    vec2 seed = (pos + v_tex_pos) * u_rand_seed;\n\n    // drop rate is a chance a particle will restart at random position, to avoid degeneration\n    float drop_rate = u_drop_rate + speed_t * u_drop_rate_bump;\n    float drop = step(1.0 - drop_rate, rand(seed));\n\n    vec2 random_pos = vec2(\n        rand(seed + 1.3),\n        rand(seed + 2.1));\n    pos = mix(pos, random_pos, drop);\n\n    // encode the new particle position back into RGBA\n    gl_FragColor = vec4(\n        fract(pos * 255.0),\n        floor(pos * 255.0) / 255.0);\n}\n";
 
 var defaultRampColors = {
     0.0: '#3288bd',

src/shaders/update.frag.glsl

@@ -42,16 +42,23 @@ void main() {
     float speed_t = length(velocity) / length(u_wind_max);
 
     // take EPSG:4236 distortion into account for calculating where the particle moved
-    float distortion = max(0.1, cos(radians(pos.y * 180.0 - 90.0)));
+    float distortion = cos(radians(pos.y * 180.0 - 90.0));
     vec2 offset = vec2(velocity.x / distortion, -velocity.y) * 0.0001 * u_speed_factor;
 
+    // update particle position, wrapping around the date line
+    pos = fract(1.0 + pos + offset);
+
     // a random seed to use for the particle drop
     vec2 seed = (pos + v_tex_pos) * u_rand_seed;
 
     // drop rate is a chance a particle will restart at random position, to avoid degeneration
-    float dropRate = u_drop_rate + speed_t * u_drop_rate_bump;
-    float drop = step(1.0 - dropRate, rand(seed));
-    pos = mix(fract(1.0 + pos + offset), vec2(rand(seed + 1.3), rand(seed + 2.1)), drop);
+    float drop_rate = u_drop_rate + speed_t * u_drop_rate_bump;
+    float drop = step(1.0 - drop_rate, rand(seed));
+
+    vec2 random_pos = vec2(
+        rand(seed + 1.3),
+        rand(seed + 2.1));
+    pos = mix(pos, random_pos, drop);
 
     // encode the new particle position back into RGBA
     gl_FragColor = vec4(