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HTML Canvas:基本操作,canvas基本操作

HTML Canvas:基本操作,canvas基本操作 HTML5 CANVAS ELEMENT Html5 canvas element <canvas id="myCanvas" width...

HTML Canvas:基本操作,canvas基本操作

  • HTML5 CANVAS ELEMENT

    Html5 canvas element

    <canvas id="myCanvas" width="500" height="300">
    

    Html5 canvas element with fallback content

    <canvas id="myCanvas" width="500" height="300">
      your browser doesn‘t support canvas!
    </canvas>
    

    2d context

    var context = canvas.getContext(‘2d‘);
    

    Webgl context (3d)

    var context = canvas.getContext(‘webgl‘);
    
  • SHAPES

    Draw rectangle

    context.rect(x, y, width, height);
    context.fill();
    context.stroke();
    

    Fill rectangle shorthand

    context.fillRect(x, y, width, height);
    

    Stroke rectangle shorthand

    context.strokeRect(x, y, width, height);
    

    Draw circle

    context.arc(x, y, radius, 0, Math.PI * 2);
    context.fill();
    context.stroke();
    
  • STYLES

    Fill

    context.fillStyle = ‘red‘;
    context.fill();
    

    Stroke

    context.strokeStyle = ‘red‘;
    context.stroke();
    

    Linear gradient

    var grd = context.createLinearGradient(x1, y1, x2, y2);
    grd.addColorStop(0, ‘red‘);   
    grd.addColorStop(1, ‘blue‘);
    context.fillStyle = grd;
    context.fill();
    

    Radial gradient

    var grd = context.createRadialGradient(x1, y1, radius1, x2, y2, radius2);
    grd.addColorStop(0, ‘red‘);
    grd.addColorStop(1, ‘blue‘);
    context.fillStyle = grd;
    context.fill();
    

    Pattern

    var imageObj = new Image();
    imageObj.onload = function() {
      var pattern = context.createPattern(imageObj, ‘repeat‘);
      context.fillStyle = pattern;
      context.fill();
    };
    imageObj.src = ‘path/to/my/image.jpg‘;
    

    Line Join

    context.lineJoin = ‘miter|round|bevel‘;
    

    Line Cap

    context.lineCap = ‘butt|round|square‘;
    

    Shadow

    context.shadowColor = ‘black‘;
    context.shadowBlur = 20;
    context.shadowOffsetX = 10;
    context.shadowOffsetY = 10;
    

    Alpha (Opacity)

    context.globalAlpha = 0.5; // between 0 and 1
    
  • COLOR FORMATS

    String

    context.fillStyle = ‘red‘;
    

    Hex Long

    context.fillStyle = ‘#ff0000‘;
    

    Hex Short

    context.fillStyle = ‘#f00‘;
    

    RGB

    context.fillStyle = ‘rgb(255,0,0)‘;
    

    RGBA

    context.fillStyle = ‘rgba(255,0,0,1)‘;
    
  • PATHS

    Begin Path

    context.beginPath();
    

    Line

    context.lineTo(x, y);
    

    Arc

    context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
    

    Quadratic curve

    context.quadraticCurveTo(cx, cy, x, y);
    

    Bezier curve

    context.bezierCurveTo(cx1, cy1, cx2, cy2, x, y);
    

    Close Path

    context.closePath();
    
  • IMAGES

    Draw Image with default size

    var imageObj = new Image();
    imageObj.onload = function() {
      context.drawImage(imageObj, x, y);
    };
    imageObj.src = ‘path/to/my/image.jpg‘;
    

    Draw image and set size

    var imageObj = new Image();
    imageObj.onload = function() {
      context.drawImage(imageObj, x, y, width, height);
    };
    imageObj.src = ‘path/to/my/image.jpg‘;
    

    Crop image

    var imageObj = new Image();
    imageObj.onload = function() {
      context.drawImage(imageObj, sx, sy, sw, sh, dx, dy, dw, dh);
    };
    imageObj.src = ‘path/to/my/image.jpg‘;
    
  • TEXT

    Fill Text

    context.font = ‘40px Arial‘;
    context.fillStyle = ‘red‘;
    context.fillText(‘Hello World!‘, x, y);
    

    Stroke Text

    context.font = ‘40pt Arial‘;
    context.strokeStyle = ‘red‘;
    context.strokeText(‘Hello World!‘, x, y);
    

    Bold Text

    context.font = ‘bold 40px Arial‘;
    

    Italic Text

    context.font = ‘italic 40px Arial‘;
    

    Text Align

    context.textAlign = ‘start|end|left|center|right‘;
    

    Text Baseline

    context.textBaseline = ‘top|hanging|middle|alphabetic|ideographic
    |bottom‘;
    

    Get Text Width

    var width = context.measureText(‘Hello world‘).width;
    
  • TRANSFORMS

    Translate

    context.translate(x, y);
    

    Scale

    context.scale(x, y);
    

    Rotate

    context.rotate(radians);
    

    Flip Horizontally

    context.scale(-1, 1);
    

    Flip Vertically

    context.scale(1, -1);
    

    Custom Transform

    context.transform(a, b, c, d ,e, f);
    

    Set Transform

    context.setTransform(a, b, c, d ,e, f);
    

    Shear

    context.transform(1, sy, sx, 1, 0, 0);
    

    Reset

    context.setTransform(1, 0, 0, 1, 0, 0);
    
  • STATE STACK

    Push State onto Stack

    context.save();
    

    Pop State off of Stack

    context.restore();
    
  • CLIPPING

    Clip

    // draw path here
    context.clip();
    
  • IMAGE DATA

    Get Image Data

    var imageData = context.getImageData(x, y, width, height);
    var data = imageData.data;
    

    Loop Through Image Pixels

    var imageData = context.getImageData(x, y, width, height);
    var data = imageData.data;
    var len = data.length;
    var i, red, green, blue, alpha;
    
    for(i = 0; i < len; i += 4) {
      red = data[i];
      green = data[i + 1];
      blue = data[i + 2];
      alpha = data[i + 3];
    }
    

    Loop Through Image Pixels With Coordinates

    var imageData = context.getImageData(x, y, width, height);
    var data = imageData.data;
    var x, y, red, green, blue, alpha;
    
    for(y = 0; y < imageHeight; y++) {
      for(x = 0; x < imageWidth; x++) {
        red = data[((imageWidth * y) + x) * 4];
        green = data[((imageWidth * y) + x) * 4 + 1];
        blue = data[((imageWidth * y) + x) * 4 + 2];
        alpha = data[((imageWidth * y) + x) * 4 + 3];
      }
    }
    

    Set Image Data

    context.putImageData(imageData, x, y);
    
  • DATA URLS

    Get Data URL

    var dataURL = canvas.toDataURL();
    

    Render Canvas with Data URL

    var imageObj = new Image();
    imageObj.onload = function() {
      context.drawImage(imageObj, 0, 0);
    };
    
    imageObj.src = dataURL;
    
  • COMPOSITES

    Composite Operations

    context.globalCompositeOperation = ‘source-atop|source-in|source-out|source-over|destination-atop|destination-in|destination-out|destination-over|lighter|xor|copy‘;

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