Question

我正在尝试创建一个在Canvas标记内绘制矩形的简单应用。我已经将Canvas调整为全屏，但每当我调整视口大小时，Canvas都会清除。我试图阻止它清除，只是保留其中的内容。有什么想法吗？

http://mediajux.com/experiments/canvas/drawing/

谢谢！

      /*
      * This is the primary class used for the application
      * @author Alvin Crespo
      */
      var app = (function(){

        var domBod          = document.body;
        var canvas          = null;
        var canvasWidth     = null;
        var canvasHeight     = null;

        return {

          //Runs after the DOM has achieved an onreadystatechange of "complete"
          initApplication: function()
          {
            //setup envrionment variables
            canvas = document.getElementById('canvas') || null;

            //we need to resize the canvas at the start of the app to be the full window
            this.windowResized();

            //only set the canvas height and width if it is not false/null
            if(canvas)
            {
              canvasWidth = canvas.offsetWidth;
              canvasHeight = canvas.offsetHeight;        
            }

            //add window events
            window.onresize = this.windowResized;   

            circles.canvas = canvas;
            circles.canvasWidth = canvasWidth;
            circles.canvasHeight = canvasHeight;
            circles.generateCircles(10);  

            setInterval(function(){
                circles.animateCircles();
            }, 50);   
          },

          /**
          * Executes Resizing procedures on the canvas element
          */
          windowResized: function()
          {
            (this.domBod === null) ? 'true' : 'false';
            try{
              console.log(canvas);
              canvas.setAttribute('width', document.body.clientWidth);
              canvas.setAttribute('height', document.body.clientHeight);        
            }catch(e) {
              console.log(e.name + " :: " + e.message);
            }
          },

          /**
          * Returns the canvas element 
          * @returns canvas
          */
          getCanvas: function()
          {
            return canvas;
          }

        };
      })();

Answer 1

设置画布宽度属性将清除画布。如果您调整样式宽度（例如canvas.style.visibility），它将缩放（通常不会以这种漂亮的方式）。如果你想让画布更大但是将元素保持原样，我建议将画布存储为图像 - 例如调用toDataURL方法获取图像，然后使用drawImage（）将其绘制到调整大小的画布。

Answer 2

以下是我使用JS3解决此问题的方法。

在内部，我将主画布和上下文分别存储为_canvas和_context。

function resize(w, h){
// create a temporary canvas obj to cache the pixel data //
    var temp_cnvs = document.createElement('canvas');
    var temp_cntx = temp_cnvs.getContext('2d');
// set it to the new width & height and draw the current canvas data into it // 
    temp_cnvs.width = w; 
    temp_cnvs.height = h;
    temp_cntx.fillStyle = _background;  // the original canvas's background color
    temp_cntx.fillRect(0, 0, w, h);
    temp_cntx.drawImage(_canvas, 0, 0);
// resize & clear the original canvas and copy back in the cached pixel data //
    _canvas.width = w; 
    _canvas.height = h;
    _context.drawImage(temp_cnvs, 0, 0);
}

JS3还提供autoSize标记，该标记会自动将画布调整为浏览器窗口或其父div的尺寸。

Answer 3

使用样式（css）设置画布大小，不要更改属性。

调整大小后全屏

Canvas将调整大小并且不会被清除，但会缩放，而不是防止缩放 - 调整大小后需要重新缩放，这里是数学：

var oldWidth    =  $("canvas").css("width").replace("px", "");
var oldHeight   = $("canvas").css("height").replace("px", "");  

$("canvas").css({ 
            "width" : window.innerWidth, 
            "height": window.innerHeight
        }); 



var ratio1 =  oldWidth/window.innerWidth;
var ratio2 =  oldHeight/window.innerHeight;



canvas.ctx.scale(ratio1, ratio2);

请注意，我从我的代码中复制粘贴并使用ids和vars名称进行一些更改，因此可能会有一些小错误，如“canvas.ctx”或dom调用。

Answer 4

我相信你已经为屏幕调整大小实现了一个监听器，并在该监听器触发时重绘了画布内容。

Answer 5

我解决这个问题的一种方法是：

const canvas = document.getElementById('ctx')
const ctx = canvas.getContext('2d')
var W = canvas.width, H = canvas.height
function resize() {
    let temp = ctx.getImageData(0,0,W,H)
    ctx.canvas.width = window.innerWidth - 99;
    ctx.canvas.height = window.innerHeight - 99;
    W = canvas.width, H = canvas.height
    ctx.putImageData(temp,0,0)
}

唯一的问题是缩小时会丢失画布之外的数据

Answer 6

我在画布上遇到了相同的问题，并且已经解决了该问题。请参考下面的代码。希望您能使用此解决问题。

注意：在参数中设置alwaysDraw: true

HTML

<div id="top-wraper">
        <div id="canvas"></div>
    </div>

    <!-- div used to create our plane -->
    <div class="plane" data-vs-id="plane-vs" data-fs-id="plane-fs">
        <!-- image that will be used as a texture by our plane -->
        <img src="texture-img.png" alt="Leo Music - Music from the heart of a Lion"/>
    </div>

JS

<script>

    function loadAnimation() {
        // set up our WebGL context and append the canvas to our wrapper
        var webGLCurtain = new Curtains("canvas");
        webGLCurtain.width = 50;
        // if there's any error during init, we're going to catch it here
        webGLCurtain.onError(function () {
            // we will add a class to the document body to display original images
            document.body.classList.add("no-curtains");
        });
        // get our plane element
        var planeElement = document.getElementsByClassName("plane")[0];
        // set our initial parameters (basic uniforms)
        var params = {
            vertexShaderID: "plane-vs", // our vertex shader ID
            fragmentShaderID: "plane-fs", // our framgent shader ID
            alwaysDraw: true,
            //crossOrigin: "", // codepen specific
            uniforms: {
                time: {
                    name: "uTime", // uniform name that will be passed to our shaders
                    type: "1f", // this means our uniform is a float
                    value: 0,
                },
            }
        }

        // create our plane mesh
        var plane = webGLCurtain.addPlane(planeElement, params);
        // if our plane has been successfully created
        // we use the onRender method of our plane fired at each requestAnimationFrame call
        plane && plane.onRender(function () {
            plane.uniforms.time.value++; // update our time uniform value
        });
    }

    window.onload = function () {
        loadAnimation();
    }


</script>

<script id="plane-vs" type="x-shader/x-vertex">
    #ifdef GL_ES
    precision mediump float;
    #endif

    // those are the mandatory attributes that the lib sets
    attribute vec3 aVertexPosition;
    attribute vec2 aTextureCoord;

    // those are mandatory uniforms that the lib sets and that contain our model view and projection matrix
    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;     
    // our texture matrix uniform (this is the lib default name, but it could be changed)
    uniform mat4 uTextureMatrix0;

    // if you want to pass your vertex and texture coords to the fragment shader
    varying vec3 vVertexPosition;
    varying vec2 vTextureCoord;

    void main() {
    vec3 vertexPosition = aVertexPosition;

    gl_Position = uPMatrix * uMVMatrix * vec4(vertexPosition, 1.0);

    // set the varyings
    // thanks to the texture matrix we will be able to calculate accurate texture coords
    // so that our texture will always fit our plane without being distorted
    vTextureCoord = (uTextureMatrix0 * vec4(aTextureCoord, 0.0, 1.0)).xy;
    vVertexPosition = vertexPosition;
    }
</script>

<script id="plane-fs" type="x-shader/x-fragment">
    #ifdef GL_ES
    precision mediump float;
    #endif

    // get our varyings
    varying vec3 vVertexPosition;
    varying vec2 vTextureCoord;
    // the uniform we declared inside our javascript
    uniform float uTime;
    // our texture sampler (default name, to use a different name please refer to the documentation)
    uniform sampler2D uSampler0;
    void main() {
    // get our texture coords
    vec2 textureCoord = vTextureCoord;
    // displace our pixels along both axis based on our time uniform and texture UVs
    // this will create a kind of water surface effect
    // try to comment a line or change the constants to see how it changes the effect
    // reminder : textures coords are ranging from 0.0 to 1.0 on both axis
    //    const float PI = 3.141592;
    const float PI = 2.0;
    textureCoord.x += (
    sin(textureCoord.x * 10.0 + ((uTime * (PI / 3.0)) * 0.031))
    + sin(textureCoord.y * 10.0 + ((uTime * (PI / 2.489)) * 0.017))
    ) * 0.0075;
    textureCoord.y += (
    sin(textureCoord.y * 20.0 + ((uTime * (PI / 2.023)) * 0.00))
    + sin(textureCoord.x * 20.0 + ((uTime * (PI / 3.1254)) * 0.0))
    ) * 0.0125;
    gl_FragColor = texture2D(uSampler0, textureCoord);
    }
</script>

<script src="https://www.curtainsjs.com/build/curtains.min.js" ></script>

调整窗口大小时防止画布清除

6 个答案: