Week3HW1

// Author: Jeremy Rotsztain
//Editor: Ziqi Guo
// Title: Week3 HW1
// Course: ShaderArt (DIGF-3011, Winter 2022)

#ifdef GL_ES
precision mediump float;
#endif

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

// calculate a circle:
// 1.0 is inside of circle (true); 0.0 is outside of circle (false)

float drawCircle(vec2 st, vec2 pos, float size){
    float d = distance(st, pos);
    // step shows values > argument 1, and we want the opposite
    // so we invert the results by subtraction 1.0 - the value
    return 1.0-smoothstep(size-(size*0.858),
                         size+(size*-0.142),
                         dot(d,d)*3.984); 
}

void main() {
    
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    st.x *= u_resolution.x/u_resolution.y;
    float change = abs(sin(u_time));//the change is from thebookofshaders 
	 vec2 mouseXY = u_mouse / u_resolution;

    // calculate layers as circles
    float layer1 = drawCircle( st, vec2(0.190,0.740-mouseXY.x), 0.260);
    float layer2 = drawCircle( st, vec2(0.5-mouseXY.x, 0.5), 0.3);
    float layer3 = drawCircle( st, vec2(0.75-mouseXY.y, 0.5), 0.3);
    
    // is is our fragment color/background color
    vec3 color = vec3(0.030,0.023,0.030);
    
    // draw 3 circles on top of one another
    color = mix( color, vec3(1.0-st.x, 0.576, change), layer1);
    color = mix( color, vec3(1.000,change,1.746-st.x), layer2);
    color = mix( color, vec3(0.0, 1.120-st.y, change), layer3);
    // color = mix( color, vec3(0.0, 0.0, 2.0), layer4);

    // debug: look at the raw data
    // disable the code below to view
    // color = vec3(layer1);
    
    // try multiplying circle2 & circle3 to create a transparent overlay

    gl_FragColor = vec4(color,1.0);
}