OVERVIEW Plain bitmap for the web Cross platform graphic manipulations High performance Mouse, touch & gamepad support Low energy consumpting animations
USAGE < ! D O C T Y P E h t m l > < h t m l > < h e a d > < t i t l e > C a n v a s ! < / t i t l e > < / h e a d > < b o d y > < c a n v a s > < / c a n v a s > < / b o d y > < / h t m l >
FALLBACK < ! D O C T Y P E h t m l > < h t m l > < h e a d > < t i t l e > C a n v a s ! < / t i t l e > < / h e a d > < b o d y > < c a n v a s > T h i s t e x t i s s h o w n , w h e n a b r o w s e r d o e s n o t s u p p o r t c a n v a s . < / c a n v a s > < / b o d y > < / h t m l >
CONTEXTS 2D context: CanvasRenderingContext2D v a r c o n t e x t = c a n v a s . g e t C o n t e x t ( ' 2 d ' ) ; WebGL context: WebGLRenderingContext v a r c o n t e x t = c a n v a s . g e t C o n t e x t ( ' w e b g l ' ) ;
API DRAWING v o i d f i l l R e c t ( x , y , w i d t h , h e i g h t ) ; v o i d s t r o k e R e c t ( x , y , w i d t h , h e i g h t ) ; v o i d c l e a r R e c t ( x , y , w i d t h , h e i g h t ) ; v o i d f i l l T e x t ( t e x t , x , y [ , m a x W i d t h ] ) ; v o i d s t r o k e T e x t ( t e x t , x , y [ , m a x W i d t h ] ) ; MDN: CanvasRenderingContext2D
API PATHS v o i d b e g i n P a t h ( ) ; v o i d c l o s e P a t h ( ) ; v o i d m o v e T o ( x , y ) ; v o i d l i n e T o ( x , y ) ; v o i d b e z i e r C u r v e T o ( c p 1 x , c p 1 y , c p 2 x , c p 2 y , x , y ) ; v o i d r e c t ( x , y , w i d t h , h e i g h t ) ; v o i d f i l l ( ) ; v o i d s t r o k e ( ) ; MDN: CanvasRenderingContext2D
API PIXEL MANIPULATION I m a g e D a t a c r e a t e I m a g e D a t a ( w i d t h , h e i g h t ) ; I m a g e D a t a g e t I m a g e D a t a ( s x , s y , s w , s h ) ; v o i d p u t I m a g e D a t a ( i m a g e d a t a , d x , d y ) ; MDN: CanvasRenderingContext2D
RETINA - HOW TO f u n c t i o n a d j u s t F o r R e t i n a ( ) { i f ( ! w i n d o w . d e v i c e P i x e l R a t i o | | w i n d o w . d e v i c e P i x e l R a t i o < = 1 ) { r e t u r n ; } v a r w i d t h = c a n v a s . w i d t h ; v a r h e i g h t = c a n v a s . h e i g h t ; c a n v a s . s t y l e . w i d t h = w i d t h + ' p x ' ; c a n v a s . s t y l e . h e i g h t = h e i g h t + ' p x ' ; c a n v a s . w i d t h = w i d t h * w i n d o w . d e v i c e P i x e l R a t i o ; c a n v a s . h e i g h t = h e i g h t * w i n d o w . d e v i c e P i x e l R a t i o ; c o n t e x t . s c a l e ( w i n d o w . d e v i c e P i x e l R a t i o , w i n d o w . d e v i c e P i x e l R a t i o ) ; }
ANIMATIONS THE OLD WAY setTimeout f u n c t i o n d r a w ( ) { / / d r a w r o u t i n e s e t T i m e o u t ( d r a w , 1 0 0 0 / 6 0 ) ; } setInterval s e t I n t e r v a l ( f u n c t i o n ( ) { / / d r a w r o u t i n e } , 1 0 0 0 / 6 0 ) ;
ANIMATIONS THE MODERN WAY requestAnimationFrame v a r a n i m a t i o n F r a m e ; f u n c t i o n s t a r t A n i m a t i o n ( ) { v a r s t e p = f u n c t i o n ( ) { / / d r a w r o u t i n e a n i m a t i o n F r a m e = w i n d o w . r e q u e s t A n i m a t i o n F r a m e ( s t e p ) ; } a n i m a t i o n F r a m e = w i n d o w . r e q u e s t A n i m a t i o n F r a m e ( s t e p ) ; } f u n c t i o n s t o p A n i m a t i o n ( ) { w i n d o w . c a n c e l A n i m a t i o n F r a m e ( a n i m a t i o n F r a m e ) ; } MDN: , requestAnimationFrame cancelAnimationFrame
ANIMATIONS PROBLEMS WITH "OLD" TECHNIQUES If the callback function takes longer than the timer will call it, the callback function gets queued. Could lead quickly to an "infinite" amount of queued callback functions. Timers continue to work in background tabs, the browser will render invisible animations (wastage of CPU and battery life). Especially bad for mobile devices. From https://dev.opera.com/articles/better-performance-with-requestanimationframe/
ANIMATIONS WHAT REQUESTANIMATIONFRAME DOES Only executed when visible to the user (will stop in background tabs!). No wastage of CPU and battery life. Frame is only drawn when browser is ready and no other frame waits for drawing. No "infinite" amount of queued callback functions. From https://dev.opera.com/articles/better-performance-with-requestanimationframe/
ANIMATIONS WHAT REQUESTANIMATIONFRAME DOESN'T DO As the name suggests: Only one frame is requested. r e q u e s t A n i m a t i o n F r a m e has to be called within the callback to get an animation loop. You don't know, when the callback will be executed. Animations on the same page, where one is in the visible area and one not, will not run synchronously since the hidden one's r e q u e s t A n i m a t i o n F r a m e will not be called. From https://dev.opera.com/articles/better-performance-with-requestanimationframe/
INTERACTION KEYBOARD & MOUSE SUPPORT Canvas supports all keyboard & mouse events like k e y d o w n , k e y u p , m o u s e d o w n or m o u s e m o v e . c a n v a s . a d d E v e n t L i s t e n e r ( ' m o u s e m o v e ' , f u n c t i o n ( m o u s e E v e n t ) { / / m o u s e e v e n t r o u t i n e } ) ; c a n v a s . a d d E v e n t L i s t e n e r ( ' k e y d o w n ' , f u n c t i o n ( k e y E v e n t ) { / / k e y d o w n e v e n t r o u t i n e } ) ; MDN: , MouseEvent KeyboardEvent
INTERACTION TOUCH Canvas supports all touch events like t o u c h s t a r t , t o u c h m o v e , t o u c h e n d . Consider using a library for recognizing gestures like . HammerJS c a n v a s . a d d E v e n t L i s t e n e r ( ' t o u c h m o v e ' , f u n c t i o n ( t o u c h E v e n t ) { / / t o u c h m o v e e v e n t r o u t i n e } ) ; MDN: , Touch events TouchEvent
EXAMPLES WITHIN GITHUB REPOSITORY 1. Basic circle 2. Circle with gradient 3. Retina support 4. requestAnimationFrame 5. Time-based animations 6. Mouse Move 7. Touch Move 8. Manipulating a rectangle with HammerJS
EXAMPLES WITHIN THE WEB Gesture recognition: Video explosion: Zen Photon Garden: Zoom Charts: Many more examples @ http://revealjs.herokuapp.com/ http://www.craftymind.com/factory/html5video/CanvasVideo http://zenphoton.com/ https://zoomcharts.com/developers/en/net- chart/examples/items/link-items.html http://www.canvasdemos.com/
SUMMARY Cross platform high-performance graphic manipulation 2D & 3D Hardware acceleration Supported by all major browsers Touch-enabled, gamepad-enabled