在 canvas 上绘制的形状在拖放事件时移动得太远
Shapes drawn on canvas moves too far when drag and drop event
我在拖动矩形时遇到了一个问题,如果我移动它只是一点点,它就会重新绘制到离当前新鼠标位置太远的地方。
如何更正距离计算?
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<head>
</head>
<body>
<canvas id="face-canvas" style="border:1px solid #000000;"></canvas>
<script type="module">
(() => {
let canvas = document.getElementById("face-canvas");
canvas.height = 300;
canvas.width = 300;
let cnt = canvas.getContext("2d");
let isDragging = false;
let offsetX = canvas.getBoundingClientRect().left;
let offsetY = canvas.getBoundingClientRect().top;
let startX = 0, startY = 0;
let selectedObjIndex = 0;
let drawn_obj = [];
drawn_obj.push({...drawBox(20, 15, 50, 50, "#1df"), index: 1})
drawn_obj.push({...drawBox(80, 40, 50, 50, "#a33"), index: 2})
document.addEventListener("mousedown", (event) => onMouseDown(event));
document.addEventListener("mousemove", (event) => onMouseMove(event));
document.addEventListener("mouseup", (event) => onMouseUp(event));
function onMouseDown(event) {
event.preventDefault();
event.stopPropagation();
startX = Math.abs(parseInt(event.clientX - offsetX));
startY = Math.abs(parseInt(event.clientY - offsetY));
selectedObjIndex = selectedObj(startX, startY);
if(selectedObjIndex > 0) {
isDragging = true;
console.log("ffffffff")
}
}
function onMouseMove(event) {
if(isDragging && selectedObjIndex > 0) {
let moveX = parseInt(event.clientX - offsetX);
let moveY = parseInt(event.clientY - offsetY);
let newX = parseInt(moveX - startX);
let newY = parseInt(moveY - startY);
drawn_obj[selectedObjIndex - 1].x += newX;
drawn_obj[selectedObjIndex - 1].y += newY;
console.log("newX, newY", newX, newY)
redrawAll();
}
}
function onMouseUp() {
event.preventDefault();
event.stopPropagation();
isDragging = false;
}
function selectedObj(x, y) {
for(let i = 0; i < drawn_obj.length; ++i) {
if(x >= drawn_obj[i].x && x <= (drawn_obj[i].x + drawn_obj[i].w) &&
y >= drawn_obj[i].y && y <= (drawn_obj[i].y + drawn_obj[i].h)) {
return drawn_obj[i].index;
}
}
return 0;
}
function redrawAll() {
cnt.clearRect(0, 0, canvas.width, canvas.height);
for(let i = 0; i < drawn_obj.length; ++i) {
drawBox(drawn_obj[i].x, drawn_obj[i].y, drawn_obj[i].w, drawn_obj[i].h, drawn_obj[i].color);
}
}
function drawBox(x, y, w, h, color) {
cnt.fillStyle = color;
cnt.fillRect(x, y, w, h);
return {x: x, y: y, w: w, h: h, color: color}
}
})();
</script>
</body>
</html>
您可以执行以下操作:
- 在顶层函数中添加两个变量作为偏移在对象中:
let objectOffsetX = 0;
let objectOffsetY = 0;
- 在收到点击事件时计算它们:
function onMouseDown(event) {
event.preventDefault();
event.stopPropagation();
startX = event.clientX - offsetX;
startY = event.clientY - offsetY;
selectedObjIndex = selectedObj(startX, startY);
objectOffsetX = startX - drawn_obj[selectedObjIndex - 1].x;
objectOffsetY = startY - drawn_obj[selectedObjIndex - 1].y;
if(selectedObjIndex > 0) {
isDragging = true;
console.log("ffffffff")
}
}
- 当鼠标移动时使用canvas偏移计算新的对象位置,对象偏移:
function onMouseMove(event) {
if(isDragging && selectedObjIndex > 0) {
let newX = event.clientX - offsetX - objectOffsetX;
let newY = event.layerY - offsetY - objectOffsetY;
drawn_obj[selectedObjIndex - 1].x = newX;
drawn_obj[selectedObjIndex - 1].y = newY;
console.log("newX, newY", newX, newY)
redrawAll();
}
}
您可能会注意到我简化了一些代码,您实际上不需要使用 parseInt
,您已经获得了(整数)数字而非字符串的所有内容。
您可以在 codepen
上看到整个过程
我在拖动矩形时遇到了一个问题,如果我移动它只是一点点,它就会重新绘制到离当前新鼠标位置太远的地方。 如何更正距离计算?
<!DOCTYPE html>
<html>
<meta charset="utf-8">
<head>
</head>
<body>
<canvas id="face-canvas" style="border:1px solid #000000;"></canvas>
<script type="module">
(() => {
let canvas = document.getElementById("face-canvas");
canvas.height = 300;
canvas.width = 300;
let cnt = canvas.getContext("2d");
let isDragging = false;
let offsetX = canvas.getBoundingClientRect().left;
let offsetY = canvas.getBoundingClientRect().top;
let startX = 0, startY = 0;
let selectedObjIndex = 0;
let drawn_obj = [];
drawn_obj.push({...drawBox(20, 15, 50, 50, "#1df"), index: 1})
drawn_obj.push({...drawBox(80, 40, 50, 50, "#a33"), index: 2})
document.addEventListener("mousedown", (event) => onMouseDown(event));
document.addEventListener("mousemove", (event) => onMouseMove(event));
document.addEventListener("mouseup", (event) => onMouseUp(event));
function onMouseDown(event) {
event.preventDefault();
event.stopPropagation();
startX = Math.abs(parseInt(event.clientX - offsetX));
startY = Math.abs(parseInt(event.clientY - offsetY));
selectedObjIndex = selectedObj(startX, startY);
if(selectedObjIndex > 0) {
isDragging = true;
console.log("ffffffff")
}
}
function onMouseMove(event) {
if(isDragging && selectedObjIndex > 0) {
let moveX = parseInt(event.clientX - offsetX);
let moveY = parseInt(event.clientY - offsetY);
let newX = parseInt(moveX - startX);
let newY = parseInt(moveY - startY);
drawn_obj[selectedObjIndex - 1].x += newX;
drawn_obj[selectedObjIndex - 1].y += newY;
console.log("newX, newY", newX, newY)
redrawAll();
}
}
function onMouseUp() {
event.preventDefault();
event.stopPropagation();
isDragging = false;
}
function selectedObj(x, y) {
for(let i = 0; i < drawn_obj.length; ++i) {
if(x >= drawn_obj[i].x && x <= (drawn_obj[i].x + drawn_obj[i].w) &&
y >= drawn_obj[i].y && y <= (drawn_obj[i].y + drawn_obj[i].h)) {
return drawn_obj[i].index;
}
}
return 0;
}
function redrawAll() {
cnt.clearRect(0, 0, canvas.width, canvas.height);
for(let i = 0; i < drawn_obj.length; ++i) {
drawBox(drawn_obj[i].x, drawn_obj[i].y, drawn_obj[i].w, drawn_obj[i].h, drawn_obj[i].color);
}
}
function drawBox(x, y, w, h, color) {
cnt.fillStyle = color;
cnt.fillRect(x, y, w, h);
return {x: x, y: y, w: w, h: h, color: color}
}
})();
</script>
</body>
</html>
您可以执行以下操作:
- 在顶层函数中添加两个变量作为偏移在对象中:
let objectOffsetX = 0;
let objectOffsetY = 0;
- 在收到点击事件时计算它们:
function onMouseDown(event) {
event.preventDefault();
event.stopPropagation();
startX = event.clientX - offsetX;
startY = event.clientY - offsetY;
selectedObjIndex = selectedObj(startX, startY);
objectOffsetX = startX - drawn_obj[selectedObjIndex - 1].x;
objectOffsetY = startY - drawn_obj[selectedObjIndex - 1].y;
if(selectedObjIndex > 0) {
isDragging = true;
console.log("ffffffff")
}
}
- 当鼠标移动时使用canvas偏移计算新的对象位置,对象偏移:
function onMouseMove(event) {
if(isDragging && selectedObjIndex > 0) {
let newX = event.clientX - offsetX - objectOffsetX;
let newY = event.layerY - offsetY - objectOffsetY;
drawn_obj[selectedObjIndex - 1].x = newX;
drawn_obj[selectedObjIndex - 1].y = newY;
console.log("newX, newY", newX, newY)
redrawAll();
}
}
您可能会注意到我简化了一些代码,您实际上不需要使用 parseInt
,您已经获得了(整数)数字而非字符串的所有内容。
您可以在 codepen
上看到整个过程