SOURCE

let x=135;
let y=10;

function setup(){
createCanvas(500,500);
colorMode(HSB,250,330,180);
}
function draw(){
if(keyIsPressed){
if(key=='q'){
x-=1;
}
else if(key=='w'){
x+=1;
}
else if(key=='a'){
y-=0.2;
}
else if(key=='s'){
y+=0.2;
}
}

if(mouseIsPressed){
stroke(x,100,100);
strokeWeight(y);
line(mouseX,mouseY,pmouseX,pmouseY);
}
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.1.9/p5.min.js"></script>