How do I create a canvas circle with a image on it?

Question

So, I followed a tutorial to make a game. Obviously, that isn't the best way to learn to code so I began to modify it. Currently the game has enemies that slowly move towards the player, but these enemies are colored circles and nothing else. I'd like to add a picture that I can put on the enemies, but I have no Idea how. Here's some code that you might like to know:

The enemy class (update is called every frame):

class Enemy {
    constructor(x, y, radius, color, velocity) {
        this.x = x;
        this.y = y;
        this.radius = radius;
        this.color = color;
        this.velocity = velocity;
    }

    draw() {
        ctx.beginPath();
        ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
        ctx.fillStyle = this.color;
        ctx.fill();
    }

    update() {
        this.draw();
        this.x = this.x + this.velocity.x;
        this.y = this.y + this.velocity.y;
    }
}

The function for creating enemies:

function spawnEnemies() {
    setInterval(() => {
        const radius = Math.random() * (30 - 4) + 4;
        let x;
        let y;
        if (Math.random() < 0.5) {
            x = Math.random() < 0.5 ? 0 - radius : canvas.width + radius;
            y = Math.random() * canvas.height;
        } else {
            y = Math.random() < 0.5 ? 0 - radius : canvas.height + radius;
            x = Math.random() * canvas.width;
        }
        const color = `hsl(${Math.random() * 360}, 50%, 50%)`;
        const angle = Math.atan2(canvas.height / 2 - y, canvas.width / 2 - x);
    const velocity = {
        x: Math.cos(angle),
        y: Math.sin(angle)
    }
        enemies.push(new Enemy(x, y, radius, color, velocity));
    }, 1000)
}

This code is ran in the animate function:

enemies.forEach((enemy, index) => {
        enemy.update();
        const dist = Math.hypot(player.x - enemy.x, player.y - enemy.y);
        
        if (isHacking) {
            if (dist - enemy.radius - player.radius < 11) {
                setTimeout(() => {
                for (let i = 0; i < enemy.radius * 2; i++) {
                    particles.push(new Particle(enemy.x, enemy.y, Math.random() * 2, enemy.color, {
                        x: (Math.random() - 0.5) * (Math.random() * 8),
                        y: (Math.random() - 0.5) * (Math.random() * 8)}
                    ));
                }}, 0)
                score += 25;
                scoreEl.innerHTML = score;
                setTimeout(() => {
                    enemies.splice(index, 1);
                    projectiles.splice(proIndex, 1);
                }, 0)
            }         
        } else if (dist - enemy.radius - player.radius < 1) {
            cancelAnimationFrame(animationId);
            modal.style.display = 'flex';
            modalScore.innerHTML = score;
        }

Also, this is my first time posting on stack overflow, so if there's something I should've done that I didn't, or vice versa, please let me know!

Where are you stuck adding these images, exactly? If you haven't made any attempt yet, maybe take a look at [How to add image to canvas](https://stackoverflow.com/questions/6011378/how-to-add-image-to-canvas) or [draw image on canvas](https://stackoverflow.com/questions/15333256/draw-image-on-canvas) — ggorlen, Mar 21 '22 at 16:28
I get stuck attempting to make an image appear ONLY in the circle. So, if I upload a rectangular picture, I want to do a border-radius sort of thing. — GreatGoldenGoat, Mar 21 '22 at 19:29
I would pre-crop the image to be a circular png with transparency if possible -- better performance. But if you want to do it in canvas, is [canvas clip image in a circle](https://stackoverflow.com/questions/15566253/canvas-clip-image-in-a-circle) what you need? (use `context.arc()` rather than `quadraticCurveTo`) — ggorlen, Mar 21 '22 at 19:32

score 1 · Answer 1 · answered Mar 21 '22 at 21:49

There are many ways to do what you want. Circle with image.

From what I can guess from your question and comments you want a dynamic circle that shows a loaded image.

Create a pattern using the image.

const imgPat = ctx.createPattern(image, "no-repeat");

Use the image size to workout the max radius you can have without going outside the image.

const minRadius = Math.min(image.width, image.height) / 2;

To draw the circle at any radius you will need to use the 2D context setTransform function. The following function will do that

function drawImageCircle(imgPat, minRadius, x, y, radius) {

     // get scale of circle image
     const scale = radius / minRadius;

     // transform to put origin at top left of bounding rectangle scaling to fit image pattern
     ctx.setTransform(scale, 0, 0, scale, x - radius, y - radius);
     ctx.fillStyle = imgPat;
     ctx.beginPath();
     ctx.arc(minRadius, minRadius, minRadius, 0, Math.PI * 2);  
     ctx.fill();

     // reset the default transform 
     ctx.setTransform(1, 0, 0, 1, 0, 0);

}

Demo

Demo loads an image. Then gets its size creates a pattern from it and animates it changing the radius and putting a 4 pixel outline around it.

const image = new Image;
image.src = "https://i.stack.imgur.com/C7qq2.png?s=256&g=1";
image.addEventListener("load", imageReady);
const ctx = canvas.getContext("2d");
var w = canvas.width, h = canvas.height, cw = w / 2, ch = h / 2;
var imgPat, minRadius;

function imageReady() {
    imgPat = ctx.createPattern(image, "no-repeat");
    minRadius = Math.min(image.width, image.height) / 2;
    requestAnimationFrame(renderLoop);
}

function drawImageCircle(imgPat, minRadius, x, y, radius) {
     const scale = radius / minRadius;
     ctx.setTransform(scale, 0, 0, scale, x - radius, y - radius);
     ctx.strokeStyle = "#F00";
     ctx.lineWidth = 8 / scale;
     ctx.fillStyle = imgPat;
     ctx.beginPath();
     ctx.arc(minRadius, minRadius, minRadius, 0, Math.PI * 2); 
     ctx.stroke();
     ctx.fill();
     ctx.setTransform(1, 0, 0, 1, 0, 0);
}

function renderLoop(time) {
    ctx.setTransform(1,0,0,1,0,0);
    ctx.clearRect(0, 0, w, h);
    var x = Math.cos(time / 500) * (cw - 80) + cw;
    var y = Math.sin(time / 600) * (ch - 80) + ch;
    var rad = Math.sin(time / 333) * 10 + 30;
    drawImageCircle(imgPat, minRadius, x, y, rad);
    requestAnimationFrame(renderLoop);
}

canvas {
   background: #888;
   border: 2px solid black;
}

<canvas id="canvas" width="256" height="256"></canvas>

ggorlen · Accepted Answer · 2022-03-21T21:49:35.593

If supportable by your use case, I suggest using a png with pre-cropped circular transparency to improve performance and avoid having to code this.

But let's carry on and answer your question from the comment. I felt this was different enough from Canvas clip image with two quadraticCurves to add a new answer, but that thread shows the general approach: use context.clip() after a path with a context.arc, then finish with context.drawImage.

Since you're drawing other things as well, wrap your clip with context.save() and context.restore() to prevent your clip from affecting everything you draw afterwards.

Here's a minimal example:

const canvas = document.createElement("canvas");
canvas.height = canvas.width = 100;
const {width: w, height: h} = canvas;
document.body.appendChild(canvas);
const ctx = canvas.getContext("2d");
const img = new Image();
img.onload = function () {
  ctx.fillRect(10, 0, 20, 20); // normal drawing before save()  
  ctx.save();
  ctx.beginPath();
  ctx.arc(w / 2, h / 2, w / 2, 0, Math.PI * 2);
  ctx.clip();
  ctx.drawImage(this, 0, 0);
  ctx.restore();
  ctx.fillRect(0, 10, 20, 20); // back to normal drawing after restore()
};
img.src = `http://placekitten.com/${w}/${h}`;

If you have multiple images, I suggest using promises as described in Images onload in one function.

How do I create a canvas circle with a image on it?

2 Answers2

Demo