HTML5画布上的文本和动画

Text and animation together on HTML5 canvas

本文关键字：文本 动画 HTML5      更新时间：2024-04-27

我有一个基于动画的画布，它在mouseover上为雨滴设置动画，在mouseout上停止动画。我有一个文本框，在提交时应该在画布上显示文本。然而，当我移动并再次鼠标悬停时，此文本将消失。我知道画布是在鼠标悬停时重新绘制的，但我不知道如何使文本保持原样。谢谢！

我已根据此处提供的解决方案调整了代码=>画布上像雨一样落下的随机图像（Javascript）

Javascript

var ctx;
var imgBg;
var imgDrops;
var x = 0;
var y = 0;
var noOfDrops = 7;
var fallingDrops = [];
var intV;
imgBg = new Image();
imgBg.src = "image.jpg";
var canvas = document.getElementById('canvasRegn');
ctx = canvas.getContext('2d');
ctx.drawImage(imgBg,0,0,600,450); //Background
function draw() {
    ctx.drawImage(imgBg, 0, 0,600,450); //Background
    for (var i=0; i< noOfDrops; i++)
    {
    ctx.drawImage (fallingDrops[i].image, fallingDrops[i].x, fallingDrops[i].y); //The rain drop
    fallingDrops[i].y += fallingDrops[i].speed;
    fallingDrops[i+4].x += fallingDrops[i].speed-1;//Set the falling speed
    if (fallingDrops[i].y > 450) {  //Repeat the raindrop when it falls out of view
    fallingDrops[i].y = -120; //Account for the image size
    fallingDrops[i].x = Math.random() * 600;    //Make it appear randomly along the width    
    }
    }
}
function setup() {
    intV = setInterval(function(){draw()}, 36);
    for (var i = 0; i < noOfDrops; i++) {
        var fallingDr = new Object();
        fallingDr["image"] =  new Image();
        fallingDr.image.src = "Rain.svg";       
        fallingDr["x"] = Math.random() * 600;
        fallingDr["y"] = Math.random() * 5;
        fallingDr["speed"] = 3 + Math.random() * 5;
        fallingDrops.push(fallingDr);
        }
}
function start(){
setup();
}
function stop(){
    clearInterval(intV);
}
function clicked(){
    var x=document.getElementById("form_val");
    ctx.clearRect(0,0,600,400);
    ctx.font="36px Verdana";
    ctx.fillStyle="yellow";
    ctx.strokeStyle="green";
    ctx.lineWidth=2;
    ctx.strokeText(x.value,200,200);
    ctx.fillText(x.value,200,200);
}

HTML

<canvas id="canvasRegn" width="600" height="450"style="margin:10px;" onmouseover="start()" onmouseout="stop()">
</canvas>
<br>
<input type="text" name="fname" size="50" id="form_val">
<button id="submit" onclick="clicked()">Submit</button>

每次你重新绘制画布时，你都需要重新绘制文本框，我会亲自重命名"clicked（）"，并从内部将其称为"draw（）"（在拖放之前或之后，取决于你想让它出现在上面还是下面）

你还必须从"clicked（）"中删除ctx.clearRect（），否则它会覆盖雨水（如果你把它放在上面）

然后你需要编辑它的调用方式，clicked（）函数可以设置一个布尔变量，该变量在draw函数中被选中（如果为true，则绘制文本框）

伪代码示例：

var text = false
draw(){
    drawRain()
    if(text == true){drawText()}
}
clicked(){
    text = true
}

然后，如果您希望文本框是可编辑的，您可以在drawText（）中使用变量而不是固定值，例如

绘图外文本（）

fontVar = "36px Verdana";
fillColour = "yellow";
strokeColour = "green";

绘图内部文本（）

ctx.font=fontVar;
ctx.fillStyle=fillColour;
ctx.strokeStyle=strokeColour;

这个问题的答案在于铺设两个画布层。第一个画布层将具有背景图像和动画效果。它上面的第二层将绘制文本。注：感谢@DBS找到解决方案。

JavaScript：

script type="text/javascript">
var ctx;
var ctx2
var imgBg;
var imgDrops;
var x = 0;
var y = 0;
var noOfDrops = 20;
var fallingDrops = [];
var intV;
fontVar ="36px Verdana";
fillColour="yellow";
strokeColour="green";
imgBg = new Image();
imgBg.src = "image.jpg";
var canvas = document.getElementById('myCanvas');
ctx = canvas.getContext('2d');
ctx.drawImage(imgBg,0,0,600,400); //Background
var canvas2 = document.getElementById('drawText');
ctx2 = canvas2.getContext('2d');
function drawing(){
ctx.drawImage(imgBg,0,0,600,400); //Background
}
function draw() {
    ctx.drawImage(imgBg, 0, 0,600,400); //Background    
    for (var i=0; i< noOfDrops; i++)
    {
    ctx.drawImage (fallingDrops[i].image, fallingDrops[i].x, fallingDrops[i].y,35,35); //The rain drop
    fallingDrops[i].y += fallingDrops[i].speed;
    fallingDrops[i+7].x += fallingDrops[i].speed-1;//Set the falling speed
    if (fallingDrops[i].y > 400) {  //Repeat the raindrop when it falls out of view
        fallingDrops[i].y = -120; //Account for the image size
        fallingDrops[i].x = Math.random() * 600;    //Make it appear randomly along the width    
        }
    }       
}

function setup() {
    intV = setInterval(function(){draw()}, 36);
    for (var i = 0; i < noOfDrops; i++) {
        var fallingDr = new Object();
        fallingDr["image"] =  new Image();
        fallingDr.image.src = "Rain.svg";       
        fallingDr["x"] = Math.random() * 600;
        fallingDr["y"] = Math.random() * 5;
        fallingDr["speed"] = 3 + Math.random() * 5;
        fallingDrops.push(fallingDr);
        }
}
function start(){
setup();
}
function stop(){
    clearInterval(intV);
}
function clicked(){
    z=document.getElementById("form_val");
    ctx2.clearRect(0,0,600,400);
    ctx2.font=fontVar;
    ctx2.fillStyle=fillColour;
    ctx2.strokeStyle=strokeColour;
    ctx2.lineWidth=2;
    ctx2.strokeText(z.value,200,200);
    ctx2.fillText(z.value,200,200);
}
</script>

HTML

<div class="wrapper">
<canvas id="myCanvas" width="600" height="400" style="margin:1px;"></canvas>
<canvas id="drawText" width="600" height="400" onmouseover="start()" onmouseout="stop()</canvas>
</div>
<br>
Greeting Message: <input type="text" name="fname" size="50" id="form_val">
<button id="submit" onclick="clicked()">Add this message</button>
</div>

CSS

如何将两块大小相同的画布叠放在一起？

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