HTML Canvas: basic operations, canvas basic operations

Source: Internet
Author: User
Tags crop image

HTML Canvas: basic operations, canvas basic operations

  • HTML5 CANVAS ELEMENTHtml5 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');
  • SHAPESDraw 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();
  • STYLESFill
    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 FORMATSString
    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)';
  • PATHSBegin 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);
    Begiscurve
    context.bezierCurveTo(cx1, cy1, cx2, cy2, x, y);
    Close Path
    context.closePath();
  • IMAGESDraw 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';
  • TEXTFill 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;
  • TRANSFORMSTranslate
    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 STACKPush State onto Stack
    context.save();
    Pop State off of Stack
    context.restore();
  • CLIPPINGClip
    // draw path herecontext.clip();
  • IMAGE processing et 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 URLSGet 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;
  • COMPOSITESComposite 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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