飞花特效

```
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>动态散花背景</title>
<meta name="description" content="Change OR Die" />

</head>

<body>

<canvas id="sakura"></canvas>

<script id="sakura_point_vsh" type="x-shader/x_vertex">
uniform mat4 uProjection;
uniform mat4 uModelview;
uniform vec3 uResolution;
uniform vec3 uOffset;
uniform vec3 uDOF;  //x:focus distance, y:focus radius, z:max radius
uniform vec3 uFade; //x:start distance, y:half distance, z:near fade start

attribute vec3 aPosition;
attribute vec3 aEuler;
attribute vec2 aMisc; //x:size, y:fade

varying vec3 pposition;
varying float psize;
varying float palpha;
varying float pdist;

//varying mat3 rotMat;
varying vec3 normX;
varying vec3 normY;
varying vec3 normZ;
varying vec3 normal;

varying float diffuse;
varying float specular;
varying float rstop;
varying float distancefade;

void main(void) {
    // Projection is based on vertical angle
    vec4 pos = uModelview * vec4(aPosition + uOffset, 1.0);
    gl_Position = uProjection * pos;
    gl_PointSize = aMisc.x * uProjection[1][1] / -pos.z * uResolution.y * 0.5;

pposition = pos.xyz;
    psize = aMisc.x;
    pdist = length(pos.xyz);
    palpha = smoothstep(0.0, 1.0, (pdist - 0.1) / uFade.z);

vec3 elrsn = sin(aEuler);
    vec3 elrcs = cos(aEuler);
    mat3 rotx = mat3(
        1.0, 0.0, 0.0,
        0.0, elrcs.x, elrsn.x,
        0.0, -elrsn.x, elrcs.x
    );
    mat3 roty = mat3(
        elrcs.y, 0.0, -elrsn.y,
        0.0, 1.0, 0.0,
        elrsn.y, 0.0, elrcs.y
    );
    mat3 rotz = mat3(
        elrcs.z, elrsn.z, 0.0, 
        -elrsn.z, elrcs.z, 0.0,
        0.0, 0.0, 1.0
    );
    mat3 rotmat = rotx * roty * rotz;
    normal = rotmat[2];

mat3 trrotm = mat3(
        rotmat[0][0], rotmat[1][0], rotmat[2][0],
        rotmat[0][1], rotmat[1][1], rotmat[2][1],
        rotmat[0][2], rotmat[1][2], rotmat[2][2]
    );
    normX = trrotm[0];
    normY = trrotm[1];
    normZ = trrotm[2];

const vec3 lit = vec3(0.6917144638660746, 0.6917144638660746, -0.20751433915982237);

float tmpdfs = dot(lit, normal);
    if(tmpdfs < 0.0) {
        normal = -normal;
        tmpdfs = dot(lit, normal);
    }
    diffuse = 0.4 + tmpdfs;

vec3 eyev = normalize(-pos.xyz);
    if(dot(eyev, normal) > 0.0) {
        vec3 hv = normalize(eyev + lit);
        specular = pow(max(dot(hv, normal), 0.0), 20.0);
    }
    else {
        specular = 0.0;
    }

rstop = clamp((abs(pdist - uDOF.x) - uDOF.y) / uDOF.z, 0.0, 1.0);
    rstop = pow(rstop, 0.5);
    //-0.69315 = ln(0.5)
    distancefade = min(1.0, exp((uFade.x - pdist) * 0.69315 / uFade.y));
}
</script>
<script id="sakura_point_fsh" type="x-shader/x_fragment">
#ifdef GL_ES
//precision mediump float;
precision highp float;
#endif

uniform vec3 uDOF;  //x:focus distance, y:focus radius, z:max radius
uniform vec3 uFade; //x:start distance, y:half distance, z:near fade start

const vec3 fadeCol = vec3(0.08, 0.03, 0.06);

varying vec3 pposition;
varying float psize;
varying float palpha;
varying float pdist;

//varying mat3 rotMat;
varying vec3 normX;
varying vec3 normY;
varying vec3 normZ;
varying vec3 normal;

varying float diffuse;
varying float specular;
varying float rstop;
varying float distancefade;

float ellipse(vec2 p, vec2 o, vec2 r) {
    vec2 lp = (p - o) / r;
    return length(lp) - 1.0;
}

void main(void) {
    vec3 p = vec3(gl_PointCoord - vec2(0.5, 0.5), 0.0) * 2.0;
    vec3 d = vec3(0.0, 0.0, -1.0);
    float nd = normZ.z; //dot(-normZ, d);
    if(abs(nd) < 0.0001) discard;

float np = dot(normZ, p);
    vec3 tp = p + d * np / nd;
    vec2 coord = vec2(dot(normX, tp), dot(normY, tp));

//angle = 15 degree
    const float flwrsn = 0.258819045102521;
    const float flwrcs = 0.965925826289068;
    mat2 flwrm = mat2(flwrcs, -flwrsn, flwrsn, flwrcs);
    vec2 flwrp = vec2(abs(coord.x), coord.y) * flwrm;

float r;
    if(flwrp.x < 0.0) {
        r = ellipse(flwrp, vec2(0.065, 0.024) * 0.5, vec2(0.36, 0.96) * 0.5);
    }
    else {
        r = ellipse(flwrp, vec2(0.065, 0.024) * 0.5, vec2(0.58, 0.96) * 0.5);
    }

if(r > rstop) discard;

vec3 col = mix(vec3(1.0, 0.8, 0.75), vec3(1.0, 0.9, 0.87), r);
    float grady = mix(0.0, 1.0, pow(coord.y * 0.5 + 0.5, 0.35));
    col *= vec3(1.0, grady, grady);
    col *= mix(0.8, 1.0, pow(abs(coord.x), 0.3));
    col = col * diffuse + specular;

col = mix(fadeCol, col, distancefade);

float alpha = (rstop > 0.001)? (0.5 - r / (rstop * 2.0)) : 1.0;
    alpha = smoothstep(0.0, 1.0, alpha) * palpha;

gl_FragColor = vec4(col * 0.5, alpha);
}
</script>

<script id="fx_common_vsh" type="x-shader/x_vertex">
uniform vec3 uResolution;
attribute vec2 aPosition;