#define TUTORIAL 2

#define PI 3.14159265359

#if TUTORIAL == 1

float linearstep(float edge0, float edge1, float x) {

    float t = (x - edge0)/(edge1 - edge0);

    return clamp(t, 0.0, 1.0);

}

float smootherstep(float edge0, float edge1, float x) {

    float t = (x - edge0)/(edge1 - edge0);

    float t1 = t*t*t*(t*(t*. - .) + .);

    return clamp(t1, 0.0, 1.0);

}

void mainImage( out vec4 fragColor, in vec2 fragCoord )

{

    vec2 r =  2.0*vec2(fragCoord.xy - 0.5*iResolution.xy)/iResolution.y;

    vec3 bgcol = vec3(1.0,0.3,0.5);//bg color

    vec3 col1 = vec3(0.4,0.2,0.5);//circle

    vec2 center1 = vec2(-1.35,);

    vec2 center2 = vec2(-0.45,);

    vec2 center3 = vec2(0.45,);

    vec2 center4 = vec2(1.35,);

    vec3 pixel = bgcol;

    float m=0.4;

    pixel = bgcol; 

    //circle 0

    //未经任何处理

    /*

    if(r.x<-0.9){

        if(length(r-center1)<m){

            pixel = col1;

        }

    }

    */

    //circle 1

    //step处理，等同于未经任何处理的circle 0

    if(r.x<-0.9){

        m =  step(m,length(r-center1));

        pixel = mix(col1,bgcol,m);

    } 

    //circle 2

    //linearstep处理

    else if(r.x<-0.0){

        m =  linearstep(m-0.005,m+0.005,length(r-center2));

        pixel = mix(col1,bgcol,m);

    }

    //circle 3

    //smoothstep处理

    else if(r.x<0.9){

           m =  smoothstep(m-0.005,m+0.005,length(r-center3));

        pixel = mix(col1,bgcol,m);

    }

    //circle 4

    //自定义smootherstep处理

    else if(r.x<1.8){

           m =  smootherstep(m-0.005,m+0.005,length(r-center4));

        pixel = mix(col1,bgcol,m);

    }

    //区域分解线

    for(float i=-0.9;i<2.0;i += 0.9){

        if(r.x<i&&r.x>i-0.005)

            pixel = vec3(1.0);

    }

    fragColor = vec4(pixel,1.0);

}

#elif TUTORIAL == 2

//绘制网格

float coordinateGrid(vec2 r) {

    float ret = 0.0;

    const float tickWidth = 0.1;

    for(float i=-2.0; i<2.0; i+=tickWidth) {

        // "i" is the line coordinate.

        ret += .-smoothstep(0.0, 0.008, abs(r.x-i));

        ret += .-smoothstep(0.0, 0.008, abs(r.y-i));

    }

    return ret;

}

//绘制长方形

float rectangle(vec2 r, vec2 topLeft, vec2 bottomRight) {

    float ret;

    float d = 0.005;

    ret = smoothstep(topLeft.x-d, topLeft.x+d, r.x);

    ret *= smoothstep(topLeft.y-d, topLeft.y+d, r.y);

    ret *= 1.0 - smoothstep(bottomRight.y-d, bottomRight.y+d, r.y);

    ret *= 1.0 - smoothstep(bottomRight.x-d, bottomRight.x+d, r.x);

    return ret;

}

//旋转函数

vec2 rotate(vec2 r, float angle){

    vec2 q;

    q.x =   cos(angle)*r.x + sin(angle)*r.y;

    q.y = - sin(angle)*r.x + cos(angle)*r.y;

    return q;

}

void mainImage( out vec4 fragColor, in vec2 fragCoord )

{

    vec2 r =  2.0*vec2(fragCoord.xy - 0.5*iResolution.xy)/iResolution.y;

    vec3 bgcol = vec3(1.0,0.5,0.5);//bg color

    vec3 col1 = vec3(0.4,0.6,0.6);//circle1

    vec3 col2 = vec3(0.4,0.2,0.5);//circle2

    vec3 pixel;

    vec2 q;

    float angle;

    angle = 0.2*PI;//旋转角度

    //左半边正常，右半边旋转

    if(r.x>0.0)

        pixel = mix(col1,bgcol,coordinateGrid(rotate(r,angle)));

    else

        pixel = mix(col1,bgcol,coordinateGrid(r));

    //绘制长方形

    pixel = mix(pixel, col2, rectangle(r, vec2(-., 0.0), vec2(-0.5, 0.5)) );

    //用rotate函数旋转方块

    pixel = mix(pixel, col2, rectangle(rotate(r,angle), vec2(0.5, -0.5), vec2(., .)) );

    fragColor = vec4(pixel,1.0);

}

#endif