别的变量都还好，就iMouse得值搞不对，我翻译过来效果也不对
const float tau = 3.14159265 * 2.;
float sqr(float x) { return x*x; }
float saw(float x) { return 2.*abs(fract(x-.5)-.5); }
// David Hoskins’ Hash without Sine https://www.shadertoy.com/view/4djSRW
//----------------------------------------------------------------------------------------
// 4 out, 2 in…
vec4 hash42(vec2 p)
{
vec4 p4 = fract(vec4(p.xyxy) * vec4(.1031, .1030, .0973, .1099));
p4 += dot(p4, p4.wzxy+33.33);
return fract((p4.xxyz+p4.yzzw)*p4.zywx);
}
//----------------------------------------------------------------------------------------
// 2 out, 1 in…
vec2 hash21(float p)
{
vec3 p3 = fract(vec3§ * vec3(.1031, .1030, .0973));
p3 += dot(p3, p3.yzx + 33.33);
return fract((p3.xx+p3.yz)*p3.zy);
}
vec4 renderSnowLayer(vec2 uv, int layer, float time, float dx)
{
vec4 col = vec4(0);
float fi = float(layer)*.25;
float tileSize = fi;
dx *= tileSize;
float fallRate = .7 / fi;
float windRate = .7 / fi;
// establish a grid, try to remove any hint of correlation between layers
vec2 tileSpace = (uv + hash21(fi) + vec2(windRate, fallRate)*time) * tileSize;
vec2 tileId = floor(tileSpace);
vec2 tileUV = fract(tileSpace);
// 4 random numbers that are constant for each snowflake & unique per layer
vec4 rnd = hash42(tileId + fi*vec2(-3.3, 5.7));
// give the snowflake a pendulum swaying motion as it falls
float flakeT = 2.*time*(.25 + .75*rnd.x) + rnd.y*tau;
flakeT = sin(flakeT)*tau/4. + tau/2.;
vec2 flakePos = .25 + .5*rnd.zw + .15*vec2(sin(flakeT),cos(flakeT));
float flakeRad = .1;
float d = distance(tileUV, flakePos) - flakeRad;
// bail early if there's nothing to do. 2*dx because fwidth needs to be defined
// up to dx, so we need an extra dx on top
//if (d > dx+dx) return col;
// put the streetlight just out of view
vec2 lightPos = vec2(1.1, 1.1);
float falloff = smoothstep(1.3, .0, sqr(distance(uv, lightPos)));
float focus = pow(dot(normalize(uv - lightPos), vec2(0,-1)),9.);
float light = mix(0.02, 1., focus * falloff);
// use a texture for the snowflake
// make sure the texture space is constant
vec2 txuv = tileUV - flakePos;
// convert to polar
float txuvr = length(txuv);
float txuva = atan(txuv.y, txuv.x);
// give it a hexagonal shape + rotating + unique angle
txuva = saw(6.*(txuva/tau+time*(rnd.x-.5)))*.5 + rnd.y*tau;
// convert back to cartesian & add an offset
//txuv = txuvr * vec2(cos(txuva),sin(txuva)) + rnd.zw*1.;
// keep the tex lookup independent of texture res
float tres = float( textureSize(iChannel0, 0).x );
// falloff radially; aim for some hexagonal edges,
// blurry foreground flakes, at least a little subtlety
float tx = smoothstep(0., sqr(txuvr*30.), texture(iChannel0, txuv*(50./tres)).x);
// accumulate
col += smoothstep(+dx, -dx, d) * vec4(light) * tx;
return col;
}
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
vec2 uv = fragCoord/iResolution.yy;
float dx = 1.*length(fwidth(uv));
float time = iTime + iMouse.x/100.;
// time of day
float t = cos(tau*time/120.)*.5+.5;
// cool night, warm day
//fragColor = vec4(.1+.7*t, .1+.65*t, .15+.55*t, 1.);
// add snow
for (int i = 1; i < 64; i++) {
fragColor += renderSnowLayer(uv, i, time, dx);
}
// fade in
if (iTime < 10.) fragColor *= smoothstep(1., 10., iTime);
fragColor.xyz = fragColor.xyz * 0.7 + texture(iChannel2, fragCoord.xy / iResolution.xy).xyz;
fragColor.xyz += step(10.,iTime) * smoothstep(.3, .1, uv.y);
fragColor.xyz += step(.6,fragColor.x) * fragColor.x;
}
