Draw Square

#ifdef GL_ES
precision mediump float;
#define GLSLIFY 1
#endif

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

#define GLSLIFY 1
#define M_SQRT_2 1.41421356
float heart(vec2 P, float size){
    float x = M_SQRT_2/2. * (P.x - P.y);
    float y = M_SQRT_2/2. * (P.x + P.y);
    float r1 = max(abs(x),abs(y))-size/3.5;
    float r2 = length(M_SQRT_2/2.*vec2(1.,-1.)-size/3.5);
    
    float r3 = length(M_SQRT_2/2.*vec2(-1.,-1.)-size/3.5);
    
    return min(min(r1,r2),r3);
}

float glow(float d, float str, float thickness){
    return thickness / pow(d, str);
}

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    // st.x *= u_resolution.x/u_resolution.y;
    st= st*2.0-1.0;
    
    // vec2 pin=vec2(st.x, -0.212*sin(st.x*20.0));//控制頻率與振幅
    // float dist=length(st-pin);
    
    st.y *= -1.;// 翻轉
    float dist=heart(st,0.796);

    vec3 color = vec3(0.);
    //1st method
    color = vec3(smoothstep(0.0,0.1,dist));
    //2nd method
    color = vec3(glow(dist, 1.0, 0.04));
    //3rd method
    color = vec3(exp(-dist*10.0));
    
    // color *= vec3(0.491,0.132,0.650);

    gl_FragColor = vec4(color,1.0);
}