如果稍微向下滚动,在 canvas 上拖动文本时出现问题
Issue when dragging text on canvas if slightly scrolled down
当我在 canvas 上稍微向下滚动时,它根本不允许我拖动文本。示例 (这些是 GIF) -
https://gyazo.com/e60d2efd924ced758c2c6441391804db
GIF 解释:所以当我在页面顶部但当我稍微向下滚动时,您看到拖动正在工作。它完全停止工作。我在周围添加了一些 console.logs,我知道 canvas 的点击事件侦听器正在工作,但是当我在页面上稍微向下滚动时它没有检测到文本。
我的拖动代码来自:http://jsfiddle.net/m1erickson/9xAGa/ |您可以看到,如果您将 canvas 尺寸更改为宽度:667 和高度:800,当您稍微向下滚动时,您将遇到与我相同的问题。
HTML代码:
<div id="middle_container">
<div class="center_container">
<canvas id="canvas" width="667px" height="800px"></canvas>
</div>
</div>
JavaScript代码:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var BB=canvas.getBoundingClientRect();
var offsetX = BB.left;
var offsetY = BB.top;
var mx;
var my;
var texts = [];
var images = [];
var dragF = -1;
var mode = "none";
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for(const { text, x, y, width, height } of texts) {
ctx.fillText(text, x, y);
}
}
function addNewText(string_text) {
var y = texts.length * 20 + 20;
var text = {
text: string_text,
x: 20,
y: y
};
ctx.font = "32px verdana";
ctx.textBaseline = "top";
text.width = ctx.measureText(text.text).width;
text.height = 32;
texts.push(text);
draw();
}
function hitDrag(x,y,textIndex) {
var r=texts[textIndex];
return (x>r.x && x<r.x+r.width && y>r.y && y<r.y+r.height);
}
function myDrag(a,e) {
if (a == "down") {
e.preventDefault();
e.stopPropagation();
mx=parseInt(e.clientX-offsetX);
my=parseInt(e.clientY-offsetY);
for(var i=0;i<texts.length;i++){
if(hitDrag(mx,my,i)){
console.log("found");
dragF = i;
}
}
}
}
addNewText("Hello World")
$("#canvas").mousedown(function(e) {
myDrag("down", e);
});
问题是这行代码:
var BB=canvas.getBoundingClientRect();
它只在您的脚本开始时填充 一次。 .getBoundingClientRect()
方法 returns HTML 元素的位置 相对于 视口。
好吧,如果您滚动 window,视口移动 - 作为 canvas 元素 - 但 BB
对象在启动时仍然保持 canvas 的位置.
修复相当简单 - 您需要通过在鼠标按下和移动时再次调用 .getBoundingClientRect()
来使用 canvas 元素的实际位置。
我根据您的代码和您链接的 fiddle 准备了一个小示例:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var BB = canvas.getBoundingClientRect();
var offsetX = BB.left;
var offsetY = BB.top;
var mx;
var my;
var texts = [];
var images = [];
var dragF = -1;
var mode = "none";
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for (const {
text,
x,
y,
width,
height
} of texts) {
ctx.fillText(text, x, y);
}
}
function addNewText(string_text) {
var y = texts.length * 20 + 20;
var text = {
text: string_text,
x: 20,
y: y
};
ctx.font = "32px verdana";
ctx.textBaseline = "top";
text.width = ctx.measureText(text.text).width;
text.height = 32;
texts.push(text);
draw();
}
function myDrag(a, e) {
if (a == "down") {
e.preventDefault();
e.stopPropagation();
let rect = canvas.getBoundingClientRect();
mx = parseInt(e.clientX - rect.left);
my = parseInt(e.clientY - rect.top);
for (var i = 0; i < texts.length; i++) {
if (hitDrag(mx, my, i)) {
// console.log("found");
dragF = i;
}
}
}
}
function hitDrag(x, y, textIndex) {
var r = texts[textIndex];
return (x > r.x && x < r.x + r.width && y > r.y && y < r.y + r.height);
}
function handleMouseMove(e) {
if (dragF < 0) {
return;
}
e.preventDefault();
let rect = canvas.getBoundingClientRect();
mouseX = parseInt(e.clientX - rect.left);
mouseY = parseInt(e.clientY - rect.top);
var dx = mouseX - mx;
var dy = mouseY - my;
mx = mouseX;
my = mouseY;
var text = texts[dragF];
text.x += dx;
text.y += dy;
draw();
}
function handleMouseUp(e) {
e.preventDefault();
dragF = -1;
}
addNewText("Hello World")
$("#canvas").mousedown(function(e) {
myDrag("down", e);
});
$("#canvas").mousemove(function(e) {
handleMouseMove(e);
});
$("#canvas").mouseup(function(e) {
handleMouseUp(e);
});
body {
background-color: ivory;
}
#canvas {
border: 1px solid red;
}
#theText {
width: 10em;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="middle_container">
<div class="center_container">
<canvas id="canvas" width="667px" height="800px"></canvas>
</div>
</div>
<br><br><br><br><br><br><br><br><br><br>
<br><br><br><br><br><br><br><br><br><br>
当我在 canvas 上稍微向下滚动时,它根本不允许我拖动文本。示例 (这些是 GIF) -
https://gyazo.com/e60d2efd924ced758c2c6441391804db
GIF 解释:所以当我在页面顶部但当我稍微向下滚动时,您看到拖动正在工作。它完全停止工作。我在周围添加了一些 console.logs,我知道 canvas 的点击事件侦听器正在工作,但是当我在页面上稍微向下滚动时它没有检测到文本。
我的拖动代码来自:http://jsfiddle.net/m1erickson/9xAGa/ |您可以看到,如果您将 canvas 尺寸更改为宽度:667 和高度:800,当您稍微向下滚动时,您将遇到与我相同的问题。
HTML代码:
<div id="middle_container">
<div class="center_container">
<canvas id="canvas" width="667px" height="800px"></canvas>
</div>
</div>
JavaScript代码:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var BB=canvas.getBoundingClientRect();
var offsetX = BB.left;
var offsetY = BB.top;
var mx;
var my;
var texts = [];
var images = [];
var dragF = -1;
var mode = "none";
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for(const { text, x, y, width, height } of texts) {
ctx.fillText(text, x, y);
}
}
function addNewText(string_text) {
var y = texts.length * 20 + 20;
var text = {
text: string_text,
x: 20,
y: y
};
ctx.font = "32px verdana";
ctx.textBaseline = "top";
text.width = ctx.measureText(text.text).width;
text.height = 32;
texts.push(text);
draw();
}
function hitDrag(x,y,textIndex) {
var r=texts[textIndex];
return (x>r.x && x<r.x+r.width && y>r.y && y<r.y+r.height);
}
function myDrag(a,e) {
if (a == "down") {
e.preventDefault();
e.stopPropagation();
mx=parseInt(e.clientX-offsetX);
my=parseInt(e.clientY-offsetY);
for(var i=0;i<texts.length;i++){
if(hitDrag(mx,my,i)){
console.log("found");
dragF = i;
}
}
}
}
addNewText("Hello World")
$("#canvas").mousedown(function(e) {
myDrag("down", e);
});
问题是这行代码:
var BB=canvas.getBoundingClientRect();
它只在您的脚本开始时填充 一次。 .getBoundingClientRect()
方法 returns HTML 元素的位置 相对于 视口。
好吧,如果您滚动 window,视口移动 - 作为 canvas 元素 - 但 BB
对象在启动时仍然保持 canvas 的位置.
修复相当简单 - 您需要通过在鼠标按下和移动时再次调用 .getBoundingClientRect()
来使用 canvas 元素的实际位置。
我根据您的代码和您链接的 fiddle 准备了一个小示例:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var BB = canvas.getBoundingClientRect();
var offsetX = BB.left;
var offsetY = BB.top;
var mx;
var my;
var texts = [];
var images = [];
var dragF = -1;
var mode = "none";
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for (const {
text,
x,
y,
width,
height
} of texts) {
ctx.fillText(text, x, y);
}
}
function addNewText(string_text) {
var y = texts.length * 20 + 20;
var text = {
text: string_text,
x: 20,
y: y
};
ctx.font = "32px verdana";
ctx.textBaseline = "top";
text.width = ctx.measureText(text.text).width;
text.height = 32;
texts.push(text);
draw();
}
function myDrag(a, e) {
if (a == "down") {
e.preventDefault();
e.stopPropagation();
let rect = canvas.getBoundingClientRect();
mx = parseInt(e.clientX - rect.left);
my = parseInt(e.clientY - rect.top);
for (var i = 0; i < texts.length; i++) {
if (hitDrag(mx, my, i)) {
// console.log("found");
dragF = i;
}
}
}
}
function hitDrag(x, y, textIndex) {
var r = texts[textIndex];
return (x > r.x && x < r.x + r.width && y > r.y && y < r.y + r.height);
}
function handleMouseMove(e) {
if (dragF < 0) {
return;
}
e.preventDefault();
let rect = canvas.getBoundingClientRect();
mouseX = parseInt(e.clientX - rect.left);
mouseY = parseInt(e.clientY - rect.top);
var dx = mouseX - mx;
var dy = mouseY - my;
mx = mouseX;
my = mouseY;
var text = texts[dragF];
text.x += dx;
text.y += dy;
draw();
}
function handleMouseUp(e) {
e.preventDefault();
dragF = -1;
}
addNewText("Hello World")
$("#canvas").mousedown(function(e) {
myDrag("down", e);
});
$("#canvas").mousemove(function(e) {
handleMouseMove(e);
});
$("#canvas").mouseup(function(e) {
handleMouseUp(e);
});
body {
background-color: ivory;
}
#canvas {
border: 1px solid red;
}
#theText {
width: 10em;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="middle_container">
<div class="center_container">
<canvas id="canvas" width="667px" height="800px"></canvas>
</div>
</div>
<br><br><br><br><br><br><br><br><br><br>
<br><br><br><br><br><br><br><br><br><br>