Canvas

HTML-5 Canvas

Agenda Where it has started What change can it bring? Understanding the lingo Basic usage Drawing shapes Using images Applying styles and colors Transformations Compositing Basic animations

History

Canvas vs SVG

High performance Everything is a pixel. Save the resulting image

as a .png or .jpg. For generating raster

graphics where pixel-level manipulation is needed.

Resolution independence Elements can be animated

using a declarative syntax, or via JavaScript.

Full control over each element

Lingo

What it is not

First kicks

<canvas id="stockGraph" width="150" height="150">

You browser doesn't support canvas.</canvas>

var canvas = document.getElementById('tutorial');if (canvas.getContext){

var ctx = canvas.getContext('2d');}

Basic shapes

Rectangle :fillRect(x,y,width,height)

strokeRect(x,y,width,height) clearRect(x,y,width,height)

Circle:arc(x, y, radius, startAngle,

endAngle, anticlockwise)

Paths

beginPath()closePath()stroke()Fill()moveTo(x, y)lineTo(x, y)

Exercise - 1

Solution

ctx.beginPath();ctx.arc(75,75,50,0,Math.PI*2,true); //

Outer circlectx.moveTo(110,75);ctx.arc(75,75,35,0,Math.PI,false); //

Mouth(clockwise)ctx.moveTo(40,75);ctx.lineTo(110,75);

ctx.moveTo(65,65);ctx.arc(60,65,5,0,Math.PI*2,true); // Left

eyectx.moveTo(95,65);ctx.arc(90,65,5,0,Math.PI*2,true); // Right

eyectx.stroke();

Beziere curves

quadraticCurveTo(cp1x, cp1y, x, y) bezierCurveTo(cp1x, cp1y, cp2x,

cp2y, x, y)

Styling

lineWidth = valuelineCap = typelineJoin = typemiterLimit = value

fillStyle = colorstrokeStyle = color

ctx.globalAlpha = 0...1;

createLinearGradient(x1,y1,x2,y2)createRadialGradient(x1,y1,r1,x2,y2,r2)addColorStop(position, color)

var ptrn =ctx.createPattern(img,'repeat');ctx.fillStyle = ptrn;

Images

var img = new Image(); img.src = 'myImage.png'; // Set source path

OR

Img = 'data:image/gif;base64,R0lGO......'

drawImage(image, sx, sy, sWidth, sHeight, dx, dy, dWidth, dHeight)

Transformations

translate(x, y)

rotate(alpha)

Compositing

globalCompositeOperation = [type]

ctx.beginPath();drawAPath(); ctx.clip();

Animate

Clear the canvas Save the canvas state Draw animated shapes Restore the canvas state

setInterval(animateShape,500);setTimeout(animateShape,500);

Canvas vs Flash