HTML5 Canvas Essentials
Steve Fulton & Jeff Fulton
Something Cool The Canvas Can Do
Demo
Easily takes a hidden video from
the HTML page, displays it
multiple times, moves each copy
Independently it around
the screen, while playing it.
Who Are We?
• Steve and Jeff Fulton (twins)
• Web developers since 1995
• Worked for Mattel Toys until 2010/2011 on all of their web
properties (Barbie, Hot Wheels, etc.) including games apps. MMOs
• Have Built over 200 games in Flash, HTML5, Mobile
• Authored of The Essential Guide To Flash Games book in 2010
• Authored of HTML 5 Canvas in 2011
• Now both working in independently on mobile, web, multi-player
HTML5, Flash, Corona games and apps
Why Move From Flash to The Canvas?
Our Story
• Finished Essential guide To Flash Games in
March 2010
• Steve Jobs refused Flash on the iOS just days
later
• Wanted to find a technology that would be
truly multi-platform and not be subject to
whims of CEOs
Why Move From Flash to The Canvas?
Our Story
• Easy Tools: a web browser, text editor and
JavaScript was all that was required.
• The HTML5 Canvas allowed for a bitmapped
graphics, much Flash’s bitmapped canvas.
• Our specific Type Of Game Development
translates well (tile sheets, bitmaps)
What is the HTML5 Canvas?
• The HTML5 Canvas is an Immediate Mode bitmapped area of the screen that can be
manipulated with JavaScript and CSS.
What Is Immediate Mode?
• Immediate Mode refers to the way the canvas
renders pixels on the screen. The HTML5
Canvas completely redraws the bitmapped
screen on every frame using Canvas API calls
from JavaScript. As a programmer, your job is
to set-up the screen display before each frame
is rendered.
What Is Retained Mode?
• Flash, Silverlight, and DOM <div>
manipulation techniques use Retained Mode.
In Retained Mode a list of individual display
objects is stored and manipulated.
HTML5 Canvas Support
• Support for the Canvas is growing. Right now we
think the best browser support goes in this order:
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–
Chrome
Safari (Mac and iOS 5)
I.E. 9 (surprised?)
Firefox
Opera
HTML5 Canvas Support : Mobile
• Support and performance has increased in 2011
• iOS 5 improved performance greatly
• Current Android performance is poor to good
depending on the device
• Windows 8/Metro is supposedly built to handle
HTML5 Canvas, and we believe that is the reason
I.E. 9 ranks so highly right now
Canvas And The DOM
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DOM : Document Object Model
Canvas is a DOM Object
Accessible via the 2D Canvas context
Has both it’s own properties and CSS
properties
What Can The Canvas Be Used for?
• Nearly anything that Flash notorious for:
– Banner Ads
– Animated Landing Pages
– Web Games
– Video
Canvas Banner Ad
• Demo
• Should be put in an <iframe>
• PNG sequence but could easily be dynamically
generated Canvas text
Animated Landing Pages
• Demo
Web Advergame
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Demo
Targets all HTML5 devices
Mobile/Web
Touch Controls Only
Video
• Demo
• Video played
Directly on Canvas
• Can Create frame counter
To trigger events
What Is It Not Good For?
• Some of Flash’s core competencies :
– Heavy, time-line based key-frame animation
– Vector motion graphics
– Secure, monetizable video
– Code/asset encapsulation
– Advanced Audio applications
– Hard Core Games (at the moment)
Why Canvas Instead Of <div>?
• Not an either/or situation
• Use the best of all the “HTML5” technologies
• For Flash AS3 developers, many algorithms translates
easily to JavaScript + Canvas
• We have already seen Canvas performance improve as
browsers improve (iOS5)
• GPUs are made to accelerate the display of the bitmaps
and 3D images (WebGL) the Canvas can create
A Quick Guide To Canvas Development
• Next we will describe the Canvas element, its’
properties and methods, then show how to
create a simple Canvas application
HTML5 Canvas Properties
Canvas Has Three Properties:
• width
• height
• id
Width and height read/write which means you
can resize the Canvas on the fly
HTML5 Canvas Methods
• getContext() : You need the context to
draw anything on the Canvas. We will see this
shortly
• toDataUrl() : Outputs the bitmapped
data of the Canvas to a string (can be used to
create a screenshot)
HTML5 Canvas And CSS
• CSS can be used in conjunction with Canvas
object itself. However, individual drawings on the
Canvas cannot be manipulated with CSS
• Example: you can scale the Canvas using CSS
style=”width: 400px; height:400px”
• Does not resize but instead scales (like setting
width ad height for a Flash embed)
Basic HTML5 Page
• Simplified greatly from HTML4
<!doctype html>
<html lang="en">
Basics HTML5 Page
CH1EX1 – Basic HTML Page
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Ch1Ex1: Basic Hello World HTML Page</title>
</head>
<body>
Hello World!
</body>
</html>
CH1EX1.html
Canvas Hello World
• Demo
Canvas Hello World
In the <body> section of the HTML page, you
add a <canvas> tag using code like the following:
<canvas id="canvasOne" width="500"
height="300">
Your browser does not support the
HTML 5 Canvas.
</canvas>
Canvas Hello World
• Setting up your Canvas app structure is very
important to get started.
• The next section is code heavy, but we believe
it is important to get a code structure down
that you can use for your apps
• Our structure is not the only way to do it
Canvas Hello World
In the <HEAD> of your HTML page, start adding JavaScript
<head>
<script type="text/javascript">
//Canvas Code Goes Here
</script>
</head>
Canvas Hello World
Testing for the Canvas Support
• We use modernizr.js to test for the Canvas support.
• Get it here: http://www.modernizr.com/
<script src="modernizr.js"></script>
<script type="text/javascript">
function canvasSupport () {
return Modernizr.canvas;
}
</script>
Canvas Hello World
We need to wait For the Browser Window To Finish
Loading so we can be sure all of the JavaScript is
available.
window.addEventListener("load",
eventWindowLoaded, false);
Canvas Hello World
After window loads, call start application:
Encapsulate Canvas code in it’s own function
object:
function eventWindowLoaded () {
canvasApp();
}
Basic Structure of Canvas Object
• Test For Canvas Support
• Get a reference to the Canvas object on the
HTML page
• Get reference to the Canvas 2D context from
the Canvas object
• Create a stub function used to draw onto the
Canvas
Canvas Hello World
Basic Structure Of Canvas App
function canvasApp () {
if (!canvasSupport()) {
return;
}
var theCanvas = document.getElementById("canvasOne");
var context = theCanvas.getContext("2d");
function draw() {
//all the cool drawing stuff goes here
}
draw()
}
Canvas Hello World
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Draw filled box as the background
Draw “stroke” box as the border
We need the Canvas context to draw anything
Since we are drawing in immediate mode, we
set Canvas context properties one at a time to
draw different objects.
Canvas Hello World
Background: yellow box, black outline
context.fillStyle = "#ffffaa";
context.fillRect(0, 0, 500, 300);
context.strokeStyle = "#000000";
context.strokeRect(5, 5, 490, 290);
Canvas Hello World
• The background is drawn first.
• Since there is no concept of a “display list” in
immediate mode, we need to make sure to draw
things in the order we want them stacked (i.e.
background first, text second)
• Advanced: globalCompositeOperation
property of the context can be manipulated for
layering purposes
Canvas Hello World
Adding Text: After drawing the boxes,
context.fillStyle is updated with a new
color. Think of this like a hand (context) with a
crayon. There is only one hand to draw with, so you
swap out the crayon (fillStyle) and draw the text.
context.fillStyle
= "#000000";
context.font
= "20px _sans";
context.fillText("Hello world!",195,80 );
Canvas Hello World
• Adding an image:
• Use JavaScript Image() object to load and
reference an image
• Use context.drawImage(imageRef, x,y)
to draw it on the Canvas
Canvas Hello World
Adding An Image:
var helloWorldImage = new Image();
helloWorldImage.onload = function () {
context.drawImage(helloWorldImage, 160, 130);
}
helloWorldImage.src = "helloworld.gif";
Canvas Hello World Redux
• Demo (again)
Text Mangler
How It Works: Interacting with HTML
• Standard HTML <form> elements
• JavaScript “change” events to call functions
• Draw() function called to re-render
Text Mangler
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Demo (apply to more than text)
Text : context.font = “64px italic bold _sans”
Resize : (canvas.width, canvas.height)
Scale : style=”width:xxx; height:xxx;” (warning!)
Alpha : (context.globalAlpha)
Gradient Fills (context.createLinearGradient())
Shadows : (context.shadowColor )
Screen Shot: canvas.toDataUrl()
Simple Animation
• To animate you need to call a function on an
interval to update the Canvas
• Drawing objects (circle, boxes), bitmapped
images, and video all need to be updated on
every frame to animate/play
Simple Animation
• Let’s use a tile sheet of a tank and animate it
driving across the screen.
• This uses a PNG file set as a tile sheet, and
interval, and some code change the position
of the tank on the Canvas
Simple Animation
• Let’s use a tile sheet of a tank and animate it
driving across the screen.
• This uses a PNG file set as a tile sheet, and
interval, and some code change the position
of the tank on the Canvas
Simple Animation
• The Tile Sheet looks like this
Simple Animation
Demo
Simple Animation
Steps:
1. First we load in the tile sheet
var tileSheet=new Image();
tileSheet.addEventListener('load', eventShipLoaded false);
tileSheet.src="tanks_sheet.png";
2. Next we set up an array of fames from the tile sheet for the tank track
var animationFrames=[1,2,3,4,5,6,7,8];
3. We create an index to use to specify which frame we are to draw
var frameIndex=0;
Simple Animation
4. We set up the rotation, x,y, dx, and dy properties for the tank
var rotation=90;
var x=50;
var y=50;
var dx=1;
var dy=0;
5. We create a listener function for the tile sheet load
function eventShipLoaded() {
startUp();
}
Simple Animation
6. The startUp() function will set up an interval to call the draw function every 100
milliseconds
function startUp(){
setInterval(drawScreen, 100 );
}
7. The draw() is code heavy. It will re-draw the background, then it will update the x
and y coordinates of the tank based on the dx and y values. Next, it will then save
the current context, draw the current frame of the tank and restore the current
context. Finally, it will update the frameIndex for the tank display.
We are rotating the tank 90 degrees, so we will also be adding in a rotation and
translation transformation.
Simple Animation
function drawScreen() {
x=x+dx;
y=y+dy;
//draw a background so we can wee the Canvas edges
context.fillStyle="#aaaaaa";
context.fillRect(0,0,500,500);
context.save();
context.setTransform(1,0,0,1,0,0)
var angleInRadians =rotation * Math.PI / 180;
context.translate(x+16, y+16)
context.rotate(angleInRadians);
Simple Animation
var sourceX=Math.floor(animationFrames[frameIndex] % 8) *32;
var sourceY=Math.floor(animationFrames[frameIndex] / 8) *32;
context.drawImage(tileSheet, sourceX, sourceY,32,32,-16,16,32,32);
context.restore();
frameIndex++;
if (frameIndex ==animationFrames.length) {
frameIndex=0;
}
}
Simple Animation Demo Again
Demo
Draw With Paths
• The easiest method to draw on the Canvas is
to create a series of paths (like vector drawing)
to depict our shapes.
• We will use the beginPath(), moveTo(),
lineTo(), stroke(), and closePath() methods to
create our shapes.
Draw With Paths
context.strokeStyle="#ff0000";
context.beginPath();
context.moveTo(100,100);
context.lineTo(150,100);
context.lineTo(150,150);
context.lineTo(100,150);
context.lineTo(100,100);
context.stroke();
context.closePath();
Draw With Paths
Demo
Rotation Transformation (Jeff)
• We can easily rotate the drawn path by applying a simple
rotation transformation.
• First we reset the Canvas transformation matrix it s “identity”
or reset value:
context.setTransform(1,0,0,1,0,0);
• Next, we set the angle we want the next path to be drawn in
with a radian value:
context.rotate(45* Math.PI / 180);
A Bit More Advanced
• Because the Canvas is an immediate mode
drawing surface, some things are vastly more
complicated than creating them in something
like Flash
• Example : Rotating an object on the Canvas
Canvas State
• The current contents of the Canvas can be
stored in a stack.
• Context.save() will save the current state
• Context.restore() will restore the previous
Canvas state.
Why?
Rotation Transformation
• We can easily rotate the drawn path by applying a simple
rotation transformation.
• First we reset the Canvas transformation matrix it s “identity”
or reset value:
context.setTransform(1,0,0,1,0,0);
• Next, we set the angle we want the next path to be drawn in
with a radian value:
context.rotate(45* Math.PI / 180);
Rotation Transformation
context.setTransform(1,0,0,1,0,0);
context.rotate(45* Math.PI / 180);
context.strokeStyle="#ff0000";
context.beginPath();
context.moveTo(100,100);
context.lineTo(150,100);
context.lineTo(150,150);
context.lineTo(100,150);
context.lineTo(100,100);
context.stroke();
context.closePath();
Rotation Transformation
Demo
What happened? The square was rotated, but the top left corner
of the Canvas was used at the origin for the rotation. Let’s fix that
with a translation transformation.
Rotation Transformation
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To rotate an object around its own center point, we must:
Translate the Canvas to the center of our object.
Draw our object 0,0 is it’s current top left corner.
If we want a 50 x 50 square that starts at 100,100, then we
must do this translation:
context.translate(125,125)
Rotation Transformation
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•
•
•
To rotate an object around its own center point, we must:
Translate the Canvas to the center of our object.
Draw our object at 0,0 as is now the current top left corner.
If we want a 50 x 50 square that starts at 100,100, then we
must do this translation:
context.translate(125,125)
Rotation Transformation
context.setTransform(1,0,0,1,0,0);
context.translate(125,125)
context.rotate(45* Math.PI / 180);
context.strokeStyle="#ff0000";
context.beginPath();
context.moveTo(0,0);
context.lineTo(50,0);
context.lineTo(50,50);
context.lineTo(0,50);
context.lineTo(0,0);
context.stroke();
context.closePath();
Rotation Transformation
Demo
What happened? We rotated the object around it’s center rather
than the top-left corner of the canvas.
Canvas State
• The current Canvas state (transformation
Matrix and Clipping region and style
attributes) can be saved with
context.save() and retrieved with
context.restore().
• The current path and current bitmap data on
the Canvas are not saved.
Canvas State
• This is useful with transformations (especially
the translations seen previously). Because a
translation effects the entire coordinate
system of the Canvas, simply resetting to the
identity (default) might not always get the
results you want. The best option is to save()
before the operation and restore() after.
Canvas State
This allows us to set the coordinate systems, all
translations, all stoke and fill attributes, etc
back to what they were before the save()
operation.
Here is an example:
Canvas State Example
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Set the fillStyle to gray
Draw a filled box
Add an image
Save state
Draw a rotated red square
Restore
Draw a yellow box that is not rotated
Canvas State
context.fillStyle="#dddddd";
context.fillRect(0,0,500,500);
var helloWorldImage = new Image();
helloWorldImage.onload = function () {
context.drawImage(helloWorldImage, 160,
130);
}
helloWorldImage.src = "helloworld.gif";
context.strokeStyle="#ffff00";
Canvas State (Jeff)
context.save()
context.translate(125,125)
context.rotate(45* Math.PI / 180);
context.strokeStyle="#ff0000";
context.beginPath();
context.moveTo(0,0);
context.lineTo(50,0);
context.lineTo(50,50);
context.lineTo(0,50);
context.lineTo(0,0);
context.stroke();
context.closePath();
context.restore();
Canvas State
context.save()
context.translate(125,125)
context.rotate(45* Math.PI / 180);
context.strokeStyle="#ff0000";
context.beginPath();
context.moveTo(0,0);
context.lineTo(50,0);
context.lineTo(50,50);
context.lineTo(0,50);
context.lineTo(0,0);
context.stroke();
context.closePath();
context.restore();
Canvas State
//new path
context.beginPath();
context.moveTo(50,50);
context.lineTo(100,50);
context.lineTo(100,100);
context.lineTo(50,100);
context.lineTo(50,50);
context.stroke();
context.closePath();
Canvas State
`
What About Adobe?
• Adobe Edge does not use Canvas (yet)
• phoneGap purchase should lead to packaging
of mobile apps with Adobe tools
• Abandoning Flash on mobile leaves the door
open for another bitmapped technology (i.e
Canvas) to be the focus
• Flash-like tool for Canvas would be ideal
Future Of Flash vs. Canvas?
• SWF format’s days are probably numbered
• Flash IDE is still an unrivaled animation tool
• Flash .flv is still best option for secure video
streams
• Air Packager is the future for games and apps
created with Flash IDE and Flex.
• Within two years, HTML5 + Canvas will most
likely rule the web page
Contact Us
• http://www.8bitrocket.com
• info@8bitrocket.com
• Twitter@8bitrocket
Power Of The Canvas
Steve Fulton & Jeff Fulton
Application Demos
• Most (but not all) of the things that Flash was
once used for can now be done on the Canvas.
• We specialize in retro style games, so these
demos are heavily geared in that direction,
but that does not mean they are the only
types of apps and games you can make
Video Puzzle
• Demo
• Slicing Up A Video
Source
Video Puzzle
• Add video to Canvas
videoElement = document.createElement("video");
videoElement.setAttribute("src",
"muirbeach.webm");
videoElement.setAttribute("loop", "true");
Video Puzzle
• To cut a part of a video element and place it on
the Canvas you would use code like this
function draw() {
…
context.drawImage(videoElement, imageX, imageY,
partWidth, partHeight, placeX, placeY,
partWidth, partHeight);
…
}
Games : Ball Battle
• Demo
• Pool Ball Physics
• Took book demo
and tried explore it as
a game
• Could be done with
Box2d Physics library
Ball Battle
• Pool Ball Physics
• Code adapted almost directly from a Flash project
• Difference is that with Flash when you set x,y
properties, the objects are instantly updated
(retained mode). With the Canvas you still need
to draw them so code needed to be adapted to
accommodate for it.
• Code is lengthy (will only show it)
Ball Battle
•
function collideBalls(ball1,ball2) {
var dx = ball1.nextx - ball2.nextx;
var dy = ball1.nexty - ball2.nexty;
var collisionAngle = Math.atan2(dy, dx);
var speed1 = Math.sqrt(ball1.velocityx * ball1.velocityx + ball1.velocityy * ball1.velocityy);
var speed2 = Math.sqrt(ball2.velocityx * ball2.velocityx + ball2.velocityy * ball2.velocityy);
var direction1 = Math.atan2(ball1.velocityy, ball1.velocityx);
var direction2 = Math.atan2(ball2.velocityy, ball2.velocityx);
var velocityx_1 = speed1 * Math.cos(direction1 - collisionAngle);
var velocityy_1 = speed1 * Math.sin(direction1 - collisionAngle);
var velocityx_2 = speed2 * Math.cos(direction2 - collisionAngle);
var velocityy_2 = speed2 * Math.sin(direction2 - collisionAngle);
var final_velocityx_1 = ((ball1.mass - ball2.mass) * velocityx_1 + (ball2.mass + ball2.mass) * velocityx_2)/(ball1.mass + ball2.mass);
var final_velocityx_2 = ((ball1.mass + ball1.mass) * velocityx_1 + (ball2.mass - ball1.mass) * velocityx_2)/(ball1.mass + ball2.mass);
var final_velocityy_1 = velocityy_1;
var final_velocityy_2 = velocityy_2
ball1.velocityx = Math.cos(collisionAngle) * final_velocityx_1 + Math.cos(collisionAngle + Math.PI/2) * final_velocityy_1;
ball1.velocityy = Math.sin(collisionAngle) * final_velocityx_1 + Math.sin(collisionAngle + Math.PI/2) * final_velocityy_1;
ball2.velocityx = Math.cos(collisionAngle) * final_velocityx_2 + Math.cos(collisionAngle + Math.PI/2) * final_velocityy_2;
ball2.velocityy = Math.sin(collisionAngle) * final_velocityx_2 + Math.sin(collisionAngle + Math.PI/2) * final_velocityy_2;
ball1.nextx = (ball1.nextx += ball1.velocityx);
ball1.nexty = (ball1.nexty += ball1.velocityy);
ball2.nextx = (ball2.nextx += ball2.velocityx);
ball2.nexty = (ball2.nexty += ball2.velocityy);
}
Ball Battle
• Uses Circle To Circle Collision detection
• Requires that each ball object be set with x, y,
radius, and preset nextX, nextY properties so
we can test before balls overlap.
Ball Battle
Circle To Circle Collision Detection
function hitTestCircle(ball1,ball2) {
var retval = false;
var dx = ball1.nextx - ball2.nextx;
var dy = ball1.nexty - ball2.nexty;
var distance = Math.sqrt(dx * dx + dy * dy);
if (distance <= (ball1.radius + ball2.radius)) {
retval = true;
}
return retval;
}
Atari 2600 Fireworks
• Demo
• Particle pool
• Pool keeps the
Numbers of active
Object minimizes to
Save memory
Fireworks Particle Pool
• Create an array to hold the particles and one
to hold an unused pool of particle object
var particlePool = new Array();
var particles = new Array();
var MAX_POOL_SIZE = 100;
Fireworks Particle Pool
Take object from Pool or create a new one
if (particlePool.length
var tempParticle
tempParticle.x =
tempParticle.y =
> 0) {
= particlePool.pop();
x;
y;
…
…
} else {
particles.push({x:x,y:y,xunits:xunits,yunits:yunits,
life:life,color:color,width:width,height:height,gravity:gr
av,moves:0,alpha:1, maxLife:life});
}
•
Fireworks Particle Pool
Add object back into pool
if (particles[i].life <= 0 ) {
if (particlePool.length < MAX_POOL_SIZE) {
particlePool.push(particles.splice(i,1));
} else {
particles.splice(i,1);
}
}
Games: Brick Basher
• Demo
• Graphics switch (g)
• A test with Gradient Fills,
Shadows on many objects
• Performance issues with
Un-optimized code
• Be sure to test in multiple
Browsers : Firefox Demo
Drag And Drop
• Demo
• Canvas CSS
Drag And Drop
Listen for Canvas “mousemove” event:
theCanvas.addEventListener("mousemove",onMou
seMove, false);
Drag And Drop
Test To see if the mouse is over any of the objects:
for (i=0; i< clickBlocks.length; i++) {
var tp = clickBlocks[i];
if ( (mouseY >= tp.y) && (mouseY <=
tp.y+tp.height) && (mouseX >= tp.x)
&& (mouseX <= tp.x+tp.width) ) {
…
}
}
Drag And Drop
Change Cursor Depending On What Mouse Is Over
theCanvas.setAttribute("style", "cursor:
pointer”);
theCanvas.setAttribute("style",
"cursor:default" );
1945
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Demo
Use images are particles
Scrolling on multiple
Layers
Multiple object pools
Spritelib Ari Feldman
http://www.widgetworx.com
Music from musopen.org
1945
(ugly) hitTest() Bounding Box. Objects need x,y, width, height
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function hitTest(image1,image2) {
r1left = image1.x;
r1top = image1.y;
r1right = image1.x + image1.width;
r1bottom = image1.y + image1.height;
r2left = image2.x;
r2top = image2.y;
r2right = image2.x + image2.width;
r2bottom = image2.y + image2.height;
retval = false;
if ( (r1left > r2right) || (r1right < r2left) || (r1bottom < r2top) || (r1top > r2bottom) ) {
retval = false;
} else {
retval = true;
}
return retval;
}
Color Drop
• Demo
• Replaced a similar a Flash game
• Since these are not DOM
Objects I found that I needed to
Create my own EventListener
class
to make this work Like Flash
• Works almost identically on
Mobile (besides sound issues)
Match 3
• Demo
• Color Drop iteration
Duck Game
• Cross Platform Web/Mobile Game
• Touch controls/mouse controls
• Replacement for Flash
Duck Game
•Created to replace a Flash game and work on
all devices.
•We add in particle effects and control that
Would work across platforms.
When doing touch (slide of finger rather than
Click, we use two separate functions for mouse
coordinate detection that in turn call the same
function for movement:allMoveHandler()
Demo
Duck Game
• Example of mouse v. touch
For Browsers:
function onMouseMove(e) {
mouseX=e.clientX-theCanvas.offsetLeft;
mouseY=e.clientY-theCanvas.offsetTop;
allMoveHandler(mouseX,mouseY);
}
Duck Game
• Example of mouse v. touch
For Mobile:
function onTouchMove(e) {
targetEvent = e.touches.item(0);
touchX=targetEvent.clientX-theCanvas.offsetLeft;
touchY=targetEvent.clientY-theCanvas.offsetTop;
allMoveHandler(touchX,touchY);
e.preventDefault();
}
Flash Header Replacement
Header Replacement
Client asked for a Flash header first, but we
suggested HTML5 so it would work crossplatform.
Flash Demo
Header Replacement
To create the HTML5 version we needed to
export all of the animations and layer the
images in the same manner as the Flash layers
to create a mask-like look to the animation.
HTML5 Version
Header Replacement
The HTML5 Mouse Pointer was simulated by
swapping out the css properties for the
Canvas when we detected the mouse over an
interactive element:
theCanvas.setAttribute("style", "cursor:pointer");
Asteroids
An arcade game like Asteroids can be created by
continually updating the Canvas and all logical objects:
Asteroids
An arcade game like Asteroids can be created
using pure path drawing, or with bitmaps, or
with a combination of both.
Path Example:
Tile Sheet Bitmap Example With Skip Timer:
Asteroids
The basic version uses a regular interval, while
the extended, color, bitmap version uses
particle pools, and a frame skip timer that
attempts to keep the frame rate as fast as
possible on various devices.
Asteroids (frame step counter)
//*** new FrameRateCounter
object prototype
function FrameRateCounter(fps) {
if (fps == undefined){
this.fps=40
}else{
this.fps=fps
}
this.lastFrameCount=0;
var dateTemp =new Date();
this.frameLast=dateTemp.getTime();
delete dateTemp;
this.frameCtr=0;
this.lastTime=dateTemp.getTime();
this.step=1;
}
Asteroids (frame step counter)
FrameRateCounter.prototype.countFrames=function() {
var dateTemp =new Date();
var timeDifference=dateTemp.getTime()-this.lastTime;
this.step=(timeDifference/1000)*this.fps;
this.lastTime=dateTemp.getTime();
this.frameCtr++;
if (dateTemp.getTime() >=this.frameLast+1000) {
this.lastFrameCount=this.frameCtr;
this.frameCtr=0;
this.frameLast=dateTemp.getTime();
}
delete dateTemp;
}
Asteroids (frame step counter)
The frame counter is called one each interval to update
the step value:
frameRateCounter.countFrames();
Individual objects use the step value to update positions:
tempParticle.x+=tempParticle.dx*frameRateCounter.step;
3D with webGL
• 3D Context
• Demo
WebGL
• The API is managed by Kronos, the same
organization that manages OpenGL. In fact,
much of WebGL is similar to programming in
OpenGL.
Some WebGL JS Libraries
•
•
•
•
•
•
Google O3D : http://code.google.com/p/o3d/
GLGE : http://www.glge.org/
C3DL : http://www.c3dl.org/
SpiderGL : http://spidergl.org/
SceneJS : http://scenejs.org/
Copperlicht :
http://www.ambiera.com/copperlicht/
Learn More About WebGL
• The best place to learn about WebGL is the
site http://learningwebgl.com/
Libraries And Tools
• Box2D - http://box2d-js.sourceforge.net/
Translated from the AS3 version
• Cocos 2D - http://cocos2d-javascript.org/about
Can handle phyics, sprites, tile maps, and more
• PhoneGap – Turn a canvas app (or and html4/5 compliant app) into a
mobile app. http://phonegap.com/
• AppMobi – Canvas acceleration using their online tools direct at game
developers http://phonegap.com/
• Impact.js – A game library for rapid game development
http://impactjs.com/
• More and more popping up every day
What’s Next?
• A Flash-like tool (Edge?) for animation
• More devices need GPU support
• Better HTML5 Audio (Zynga Jukebox? Uses
Flash as Fallback)
• Camera/Microphone support
• What would you like to see next?
Contact Us
• http://www.8bitrocket.com
• info@8bitrocket.com
• Twitter@8bitrocket