Say I have a triangle made with 3 points.
makeTriangle(x1, y1, x2, y2, x3, y3);
How do I check if said triangle contains the a certain set of points?
I'm trying to make an interactive UI with P5.js that includes an arrow that allows you to resize the object. The wireframe code is:
let Size, x, y, moving;
//runs once at the start of the program
function setup() {
createCanvas(400, 400);
Size = 100;
x = 10;
y = 10;
moving = false;
}
//runs once every frame
function draw() {
background(220);
handleMouse();
fill("grey");
noStroke();
square(x, y, Size, 5);
fill("black");
triangle( x + Size * 0.9, y + Size * 0.9,
x + Size * 0.7, y + Size * 0.9,
x + Size * 0.9, y + Size * 0.7 );
}
function handleMouse(){
if(mouseInTriangle(/* x1, y1, x2, y2, x3, y3 */) && mouseIsPressed || mouseIsPressed && moving){
moving = true;
} else {
moving = false;
}
if(moving){
Size = max((mouseX + mouseY)/2 + x + y, 50);
}
}
function mouseInTriangle(x1, y1, x2, y2, x3, y3){
//Is mouse in triangle?
return true;
}<script src="https://cdn.jsdelivr.net/npm/p5@1.4.1/lib/p5.js"></script>Is there a dynamic way to tell if a point is within a triangle?
I suggest to use an algorithm that compares the areas of triangles. See Check whether a given point lies inside a triangle or not.If the point is in a triangle, that point divides the triangle into 3 smaller triangles. Calculate the sum of the areas of these 3 triangles and compare it to the area of the originally triangle:
function getArea(a, b, c) {
return abs((a[0]*(b[1]-c[1]) + b[0]*(c[1]-a[1])+ c[0]*(a[1]-b[1]))/2);
}
function mouseInTriangle(x1, y1, x2, y2, x3, y3){
let point = [mouseX, mouseY];
let area = getArea([x1, y1], [x2, y2], [x3, y3]);
let areaA = getArea([x1, y1], [x2, y2], point);
let areaB = getArea(point, [x2, y2], [x3, y3]);
let areaC = getArea([x1, y1], point, [x3, y3]);
return abs(areaA + areaB + areaC - area) < 0.001;
}
let x1, y1, x2, y2, x3, y3;
let Size, x, y, moving;
//runs once at the start of the program
function setup() {
createCanvas(400, 400);
Size = 100;
x = 10;
y = 10;
moving = false;
}
//runs once every frame
function draw() {
background(220);
handleMouse();
fill("grey");
noStroke();
square(x, y, Size, 5);
fill("black");
x1 = x + Size * 0.9;
y1 = y + Size * 0.9;
x2 = x + Size * 0.7;
y2 = y + Size * 0.9;
x3 = x + Size * 0.9;
y3 = y + Size * 0.7;
triangle(x1, y1, x2, y2, x3, y3);
}
function handleMouse(){
if(mouseIsPressed && (moving || mouseInTriangle(x1, y1, x2, y2, x3, y3))) {
moving = true;
Size = max((mouseX + mouseY)/2 + x + y, 50);
} else {
moving = false;
}
}
function getArea(a, b, c) {
return abs((a[0]*(b[1]-c[1]) + b[0]*(c[1]-a[1])+ c[0]*(a[1]-b[1]))/2);
}
function mouseInTriangle(x1, y1, x2, y2, x3, y3){
let point = [mouseX, mouseY];
let area = getArea([x1, y1], [x2, y2], [x3, y3]);
let areaA = getArea([x1, y1], [x2, y2], point);
let areaB = getArea(point, [x2, y2], [x3, y3]);
let areaC = getArea([x1, y1], point, [x3, y3]);
return abs(areaA + areaB + areaC - area) < 0.001;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.4.1/p5.min.js"></script>