像素精灵元素GLSL - 35-绘制魔术环（the magician）

绘制魔术环

示例代码

#ifdef GL_ES
precision mediump float;
#endif

uniform float u_time;
uniform vec2 u_resolution;
uniform vec2 u_mouse;

float QTR_PI = 0.78539816339;                       // 四分之一PI
float HALF_PI = 1.5707963267948966192313216916398;  // 二分之一PI
float PI = 3.1415926535897932384626433832795;       // PI 
float TWO_PI = 6.2831853071795864769252867665590;  // 2PI
float TAU = 6.2831853071795864769252867665590;  // 2PI
float PHI = 1.618033988749894848204586834;  // 黄金分割率
float EPSILON = 0.0000001;

/** 绘制线条
* @param {float } x 坐标点
* @param {float } s 划线的位置
* @param {float } w 现对与屏幕宽度的线宽
*/
float stroke(float x, float s, float w){
    float d = step(s, x + w * 0.5) - step(s, x - w * 0.5);
    return clamp(d, 0.0, 1.0);
}


/** 绘制一个圆
* @param st 坐标点
*/
float circleSDF(vec2 st){
    return length(st-0.5) * 2.0;
}

/**
* @param v 坐标值
* @param pct 十字大小
*/
float flip(float v, float pct){
    return mix(v, 1.0 - v, pct);
}

/**
* @param st 坐标值
* @param s 区域大小
*/
float rectSDF(vec2 st, vec2 s){
    st = st * 2.0 -1.0;
    return max(abs(st.x / s.x), abs(st.y / s.y));
}


vec3 bridge(vec3 c, float d, float s, float w){
    c *= 1.0 - stroke(d, s, w * 2.0);
    return c + stroke(d, s, w);
}


void main(){
    vec2 st = gl_FragCoord.xy / u_resolution;
    st.x *= u_resolution.x/u_resolution.y;
    st.y *= u_resolution.y/u_resolution.x;

    vec3 color = vec3(0.0); 

    st.x = flip(st.x, step(0.5, st.y));
    vec2 offset = vec2(0.15, 0.0);
    float left = circleSDF(st + offset);
    float right = circleSDF(st - offset);
    color += stroke(left, 0.4, 0.075);
    color = bridge(color, right, 0.4, 0.075);

    gl_FragColor = vec4(color, 1.0);
}

代码效果

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