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HTML5 Examples drawing on canvas (paths, text, video), mouse events, timed events, objects, semantic elements, etc.

Google tools for webmasters

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Page 1: Google tools for webmasters

HTML5 Examplesdrawing on canvas (paths, text, video), mouse events, timed events, objects,

semantic elements, etc.

Page 2: Google tools for webmasters

Overview• Background• Show and explain 4 examples, focus on

o drawing paths (lines & arcs), rectangles & text on canvaso semantic elements o use of CSS for font families, decoration, color of texto translate, scale coordinate systemo object oriented programming to produce stub application for dragging of

'objects' using mouse eventso change of cursor icono video elements and drawing video on canvaso timed eventso structured way for sequence of drawings

Page 3: Google tools for webmasters

Background• HTML5 is next new thing...still in development

o canvas, video, semantic elements, events, etc.• Browser support mixed

o Firefox, Safari, Chrome, Opera ahead of IEo Firefox NOT always ahead, but it does have Error Console

• Formal W3C document is not easy to decipher...but/and many on-line sources, including you!

• My background: early career at IBM Research in robotics and manufacturing, now in academia, teaching math/cs, new media and also general education courses. I like programming!

Page 4: Google tools for webmasters

Examples• HTML5 logo, with scaling and use of CSS formatted footer

http://faculty.purchase.edu/jeanine.meyer/html5/html5logoscale.html• Application stub: drawing rectangles and ovals, drag and

drop http://faculty.purchase.edu/jeanine.meyer/html5/build1.html• Bouncing video masked to be a circle 

http://faculty.purchase.edu/jeanine.meyer/html5/videobounce.html • Origami

http://faculty.purchase.edu/jeanine.meyer/html5/origamifrog.htmlhttp://faculty.purchase.edu/jeanine.meyer/html5/origamifish.html

Page 5: Google tools for webmasters

NOTE on these and other HTML5 examplesYou always can look at the source using the View source option in the browser.

Complex examples may have separate and multiple files, especially for CSS and JavaScript.

Most people are open to comments. I sometimes write tutorials...

Page 6: Google tools for webmasters

HTML5 logo • use beginPath, moveTo, lineTo, fill to draw shield

• built on other work (they had  the x,y positions for the shield, but no HTML) and this motivated a use of translate

• added slider (new input type) -- use of another coordinate transformation: scale

• used drawing text on canvas and [regular] text

• used article and footer (CSS formatting)

Page 7: Google tools for webmasters

Organization of dologo

text (HTML)

5 sided orange background right hand, lighter orange part of background light gray, left hand side part of the 5:  2 paths white, right hand side of the 5: 2 paths

Page 8: Google tools for webmasters

Code snippets for logo<input id="slide" type="range" min="0" max="100" value="100" onChange="changescale(this.value)" step="10"/> function changescale(val) {factorvalue = val / 100;dologo(); } function dologo() {    var offsety = 80 ;    ctx.restore();    ctx.save();    ctx.clearRect(0,0,600,400);    ctx.scale(factorvalue,factorvalue);    ctx.fillText("HTML", 31,60);    ctx.translate(0,offsety);            ...                                        

Page 9: Google tools for webmasters

dologo, cont.

ctx.fillStyle = "#E34C26";   // given in W3C specctx.beginPath(); ctx.moveTo(39, 250); ctx.lineTo(17, 0); ctx.lineTo(262, 0); ctx.lineTo(239, 250); ctx.lineTo(139, 278); ctx.closePath(); ctx.fill(); 

....

Page 10: Google tools for webmasters

CSS for footer, article<style> footer {display:block; border-top: 1px solid orange; margin: 10px; font-family: "Trebuchet MS", Arial, Helvetica, sans-serif; font-weight: bold; }  article {display:block; font-family: Georgia, "Times New Roman", Times, serif; margin: 5px;} </style>

NOTES The border-top puts an orange line before footer. The two font-family directives provide back-up. The display:block directives provide the line breaks.

Page 11: Google tools for webmasters

Building and moving shapes (stub for application)• Use object style of

programming + display listo Rect and Ovalo constructor, draw,

move, check-for-collision methods

• Using mouse events requires access to accurate mouse position

• Changed cursor icon

 

Page 12: Google tools for webmasters

init (invoked by onLoad in <body> )

function init() {  canvas1 = document.getElementById('canvas');  canvas1.onmousedown = function () { return false; };       canvas1.addEventListener('mousedown',startdragging,false);  ctx = canvas1.getContext("2d"); 

 var r1 = new Rect(10,10,100,200,"red");  var s1 = new Rect(30,200, 50,50,"blue");  var oval1 = new Oval(200,350,60,2.0,1.0, "teal");  var cir1 = new Oval(300,200,100,1.0,1.0,"brown"); 

 stuff.push(r1);  stuff.push(s1);  stuff.push(oval1);  stuff.push(cir1);  drawstuff(); } 

Page 13: Google tools for webmasters

drawstuff function

function drawstuff() {        ctx.clearRect(0,0,600,500);        for (var i=0;i<stuff.length;i++) {             stuff[i].draw();        }   } 

Code expects that each element of step will have a draw method...

Page 14: Google tools for webmasters

Constructor function for ovals 

function Oval(x,y,r,hor,ver,c) {    this.x = x;    this.y = y;    this.r = r;    this.hor = hor;    this.ver = ver;    this.move = move;    this.draw = drawoval;    this.color = c;    this.overcheck = checkoval;}

Page 15: Google tools for webmasters

draw method for oval shapesfunction drawoval() {   ctx.save();   ctx.translate(this.x,this.y);   ctx.scale(this.hor,this.ver);    ctx.fillStyle = this.color;    ctx.beginPath();    ctx.arc(0,0,this.r,0,2*Math.PI,true);   ctx.closePath();   ctx.fill();   ctx.restore();  }

Page 16: Google tools for webmasters

definition of [what will be] overcheck methodfunction checkoval(mx,my) {//computes positions in translated &scaled coordinate systemvar x1 = 0;  //this is this.x - this.xvar y1 = 0;var x2 = (mx-this.x)/this.hor;var y2 = (my-this.y)/this.ver;if (distsq(x1,y1,x2,y2)<=(this.r*this.r) ){   return true} else {   return false }}

Page 17: Google tools for webmasters

Video bouncing in a box• Current situation for native

support of video requires 3 video files for distinct codecs

• Use setIntervalo video captured at

different frames• drawImage to put video

on canvas with a shape (filled in paths) moving in sync to be a mask

• mask with hole works in Firefox, Opera but need two-paths for Chrome

see props

 

Page 18: Google tools for webmasters

setup including animaitonfunction init(){   ctx = document.getElementById('canvas').getContext('2d');   v = document.getElementById("vid");   v.addEventListener("ended",restart,false);     // because loop doesn't work on FF 

  v.width = v.videoWidth/3;   v.height = v.videoHeight/3;   videow = v.width;   videoh = v.height;   maskrad = .4*Math.min(videow,videoh);   ctx.lineWidth = ballrad;   ctx.strokeStyle ="rgb(200,0,50)";   ctx.fillStyle="white";   v.play();   setInterval(drawscene,50);  } 

Page 19: Google tools for webmasters

Code/markup for videoIn body element<video id="vid" loop="loop" preload="auto"> <source src="joshuahomerun.mp4" type='video/mp4; codecs="avc1.42E01E, mp4a.40.2"'> <source src="joshuahomerun.webmvp8.webm" type='video/webm; codec="vp8, vorbis"'>  <source src="joshuahomerun.theora.ogv" type='video/ogg; codecs="theora, vorbis"'> Your browser does not accept the video tag.  </video>

In script element, in init function...v = document.getElementById("vid"); 

In script element, in drawscene, strategy is  erase canvas  draw video ctx.drawImage(v,ballx+boxx, bally+box, v.width,v.height);  draw (white) filled in path to be the mask

Page 20: Google tools for webmasters

ctx.beginPath(); ctx.moveTo(ballx+boxx,bally+boxy); ctx.lineTo(ballx+boxx+v.width,bally+boxy); ctx.lineTo(ballx+boxx+v.width,bally+boxy+.5*v.height); ctx.lineTo(ballx+boxx+.5*v.width+maskrad, bally+boxy+.5*v.height); ctx.arc(ballx+boxx+.5*v.width,bally+boxy+.5*v.height,maskrad,0,     Math.PI,true); ctx.lineTo(ballx+boxx,bally+boxy+.5*v.height); ctx.lineTo(ballx+boxx,bally+boxy); ctx.fill(); ctx.moveTo(ballx+boxx,bally+boxy+.5*v.height); ctx.lineTo(ballx+boxx,bally+boxy+v.height); ctx.lineTo(ballx+boxx+v.width,bally+boxy+v.height); ctx.lineTo(ballx+boxx+v.width,bally+boxy+.5*v.height); ctx.lineTo(ballx+boxx+.5*v.width+maskrad,bally+boxy+.5*v.height); ctx.arc(ballx+boxx+.5*v.width,bally+boxy+.5*v.height,maskrad,    0,Math.PI,false); ctx.lineTo(ballx+boxx,bally+boxy+.5*v.height); ctx.fill();

Page 21: Google tools for webmasters

Origami 

• General system for origami directions o mountain fold lineo valley fold lineo other utility functions 

• Use array to hold steps, a step being a function that draws and a text string

• Geometry, trig & algebra to determine coordinates

• Use mainly paths on canvas plus a photograph & videos

• My hobby but/and great example of mathematics AND programming!

 

Page 22: Google tools for webmasters

Organize steps

• Use steps array• Each element is itself an array, consisting of the name of a

function that produces the drawing (or the photo or the video) and a piece of text.

var steps = [    [directions,"Diagram conventions"],    [showkami,"Make quarter turn."],    [diamond1,"Fold top point to bottom point."],    [triangleM,"Divide line into thirds and make valley folds and unfold "],   [thirds,"Fold in half to the left."],  ...

• I developed these step by step, including going back and inserting new steps demonstration of iterative design.

Page 23: Google tools for webmasters

thirds() 

function thirds() {   triangle();   skinnyline(ex,ey,gx,gy);   skinnyline(fx,fy,hx,hy);   curvedarrow(cx,cy,ax,ay,0,-20);   valley(jx,jy,dx,dy,"orange"); } 

Page 24: Google tools for webmasters

The donext (step) function

function donext() {   if (nextstep>=steps.length) {      nextstep=steps.length-1;   }  v.pause();  v.style.display = "none";  //erases last video played  canvas1.height = 480;  //restore height  ctx.clearRect(0,0,cwidth,cheight);  ctx.lineWidth = origwidth;  steps[nextstep][0]();   //invokes the function  ta.innerHTML = steps[nextstep][1];  nextstep++;}  

Page 25: Google tools for webmasters

                                    Thank you!