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HTML5 Canvas - The Future of Graphics on the Web
The document discusses the HTML5 Canvas, highlighting its role as a 2D drawing platform in web browsers that utilizes JavaScript and HTML without the need for plugins. It covers the differences between bitmap (canvas) and vector (SVG) systems, explaining its capabilities for data visualization, animations, web applications, and games. The document also outlines how to start using canvas, draw shapes, manage complex paths, and hints at its future potential against Flash, emphasizing the importance of frameworks for animation and development.
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HTML5 Canvas - The Future of Graphics on the Web
- 1. HTML5 Canvas The Future of Graphics on the Web
- 2. Rob Hawkes @robhawkes for you social media folk rawkes.com if you want to see more The place to be Yes, that’s me looking horrible AKA. Layabout Guess my middle name
- 3. “Canvas is myfavourite part of HTML5, alongside its video and audio support” Myself, at some point
- 4. So what iscanvas?
- 5. An overview ofcanvas ✽ 2D drawing platform within the browser ✽ Uses nothing more than JavaScript and HTML – no plugins ✽ Extensible through a JavaScript API ✽ Created by Apple for dashboard widgets ✽ Now openly developed as a W3C spec
- 6. Bitmap vs. vector ✽ Canvas is a bitmap system • Everything is drawn as a single, flat, picture • Changes require the whole picture to be redrawn ✽ SVG is a vector system • Elements to be drawn are separate DOM objects • They can be manipulated individually ✽ SVG isn’t part of HTML5 • Future isn’t as rosy as canvas’
- 7. Browser support ✽ Most modern browsers • Safari • Chrome • Firefox • Opera ✽ No Internet Explorer support by default • However, there are hacks to get it working
- 8. What is itfor?
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- 13. Here’s something Imade earlier
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- 15. Created using thenew HTML5 tag <canvas height=”600” width=”800”></canvas> Height and width need to be set explicitly
- 16. (0,0) x y Uses the standard screen-based coordinate system
- 17. Everything is drawnonto the 2D rendering context (ctx) 2D rendering context Canvas
- 18. Use getContext() toaccess the 2D rendering context var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); This is your friend
- 19. ctx.fillStyle = 'rgb(255,0, 0)'; ctx.strokeStyle = 'rgba(0, 255, 0, 0.5)'; Use RGBA for alpha transparency fillStyle() and strokeStyle() define the style of shapes to be drawn
- 20. Simple shapes Method Action fillRect(x, y, w, h) Draws a rectangle using the current fill style strokeRect(x, y, w, h) Draws the outline of a rectangle using the current stroke style clearRect(x, y, w, h) Clears all pixels within the given rectangle Simple shapes are drawn without effecting the current path
- 21. ctx.fillStyle = ‘rgb(65,60, 50)’; ctx.fillRect(25, 50, 100, 100); ctx.strokeStyle = ‘rgb(65, 60, 50)’; ctx.strokeRect(130, 500, 40, 70); 500 130
- 22. Complex shapes &paths ✽ Paths are a list of subpaths ✽ Subpaths are one or more points connected by straight or curved lines ✽ Rendering context always has a current path ✽ A new path should be created for each individual shape
- 23. Complex shapes &paths Method Action beginPath() Resets the current path closePath() Closes the current subpath and starts a new one moveTo(x, y) Creates a new subpath at the given point fill() Fills the subpaths with the current fill style stroke() Outlines the subpaths with the current stroke style
- 24. Complex shapes &paths Method Action lineTo(x, y) Draws a straight line from the previous point rect(x, y, w, h) Adds a new closed rectangular subpath arc(x, y, radius, startAngle, Adds a subpath along the circumference of endAngle, anticlockwise) the described circle, within the angles defines arcTo(x1, y1, x2, y2, radius) Adds a subpath connecting two points by an arc of the defined radius bezierCurveTo(cp1x, cp1y, Adds a cubic Bézier curve with the given cp2x, cp2y, x, y) control points quadraticCurveTo(cpx, Adds a quadratic Bézier curve with the given cpy, x, y) control points
- 25. ctx.strokeStyle = ‘rgb(65,60, 50)’; ctx.beginPath(); ctx.moveTo(50, 50); ctx.lineTo(100, 100); ctx.stroke(); 50 50 100 100
- 26. ctx.fillStyle = ‘rgb(65,60, 50)’; ctx.beginPath(); ctx.arc(100, 100, 30, 0, Math.PI*2, true); ctx.fill(); 100 100 30
- 27. ctx.strokeStyle = ‘rgb(65,60, 50)’; ctx.beginPath(); ctx.moveTo(50, 100); ctx.bezierCurveTo(70, 50, 130, 150, 150, 100); ctx.stroke(); cp1 100 50 cp2
- 28. Other cool stuff ✽ Text ✽ Shadows & blurring ✽ Line styles; width, cap, etc. ✽ Saving state of drawing context ✽ Transformations
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- 30. Images can bedrawn onto the canvas ctx.drawImage(image, dx, dy); ctx.drawImage(image, dx, dy, dw, dh); ctx.drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh); sy sx sh dy sw dx Canvas dh dw Source image
- 31. Individual pixel valuescan be retrieved ctx.getImageData(sx, sy, sw, sh); sy sx Returns an array sh of pixel values sw
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- 34. Harnessing the power ✽ Remember all the shapes on the canvas ✽ Move them, transform them, and make them interact ✽ Redraw the all the shapes in their new positions ✽ Rinse and repeat, really quickly
- 35. My workflow ✽ Treat each shape as a JavaScript object ✽ Each shape object has position values ✽ Store the shape objects in an array ✽ Run a timeout function every 40 ms ✽ Clear the canvas ✽ Make any changes to the shape objects ✽ Loop through and redraw every shape
- 36. The future ofcanvas
- 37. The future ofcanvas ✽ OOP programming allows much to be achieved through canvas ✽ It’s flexible and powerful • Animation engines • Pseudo 3D graphics ✽ Reading pixel values opens a lot of doors ✽ Integration with other HTML5 elements is a killer feature
- 38. Is it aFlash killer?
- 39. Canvas vs. Flash ✽ Canvas will flourish with future development of frameworks ✽ Its animation capabilities are only just being realised ✽ Flash has tight integration with the offline world, but HTML5 is changing that ✽ There is a gap in the market for a GUI for developing canvas applications
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