<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Canvas拖动方块</title>
</head>
<body>
<canvas id="canvas" width="500" height="500" style="border:1px solid red;"></canvas>
<script>
const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
let startX, startY;
let isDrawing = false;
const rects = [];
let selectedSquare = null;
let offsetX, offsetY;
function findSquare(x, y) {
for (let i = rects.length - 1; i >= 0; i--) {
const square = rects[i];
if (x >= square.x && x <= square.x + square.w &&
y >= square.y && y <= square.y + square.h) {
return square;
}
}
return null;
}
canvas.addEventListener('mousedown', (e) => {
const mouseX = e.clientX - canvas.getBoundingClientRect().left;
const mouseY = e.clientY - canvas.getBoundingClientRect().top;
selectedSquare = findSquare(mouseX, mouseY);
if (selectedSquare) {
console.log("drag start");
offsetX = mouseX - selectedSquare.x;
offsetY = mouseY - selectedSquare.y;
}else{
startX = e.offsetX;
startY = e.offsetY;
isDrawing = true;
}
});
canvas.addEventListener('mousemove', (e) => {
if (selectedSquare) {
console.log("drag");
const mouseX = e.clientX - canvas.getBoundingClientRect().left;
const mouseY = e.clientY - canvas.getBoundingClientRect().top;
selectedSquare.x = mouseX - offsetX;
selectedSquare.y = mouseY - offsetY;
}else{
if(!isDrawing) return;
const x = e.offsetX;
const y = e.offsetY;
const w = x - startX;
const h = y - startY;
drawRect(startX, startY, w, h);
}
});
canvas.addEventListener('mouseup', (e) => {
if(selectedSquare){
selectedSquare = null;
}else{
isDrawing = false;
rects.push({
x: startX,
y: startY,
w: e.offsetX - startX,
h: e.offsetY - startY
});
}
});
function drawRect(x, y, w, h) {
ctx.beginPath();
ctx.rect(x, y, w, h);
ctx.fill();
}
function update() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for(let rect of rects) {
drawRect(rect.x, rect.y, rect.w, rect.h);
}
requestAnimationFrame(update);
}
update();
</script>
</body>
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