javascript - Html 5 canvas trouble -


i'm trying practice html5 canvas drawing came this. should result in yellow star overlapped green silhouette of bust (the head , shoulders of person).

however if drawstar() line un-commented, green silhouette not drawn. working code not important explanation of happening.

http://jsfiddle.net/xiondark2008/lyfhj/2/

html:

<!doctype html> <html> <head>     <style>     h6{         -webkit-margin-before: .5em;         -webkit-margin-after: 0;     }     label{         margin-left: 1em;     }     </style>  </head> <body>      <canvas id="mycanvas" width="19" height="19"          style="border:1px solid d3d3d3;">         browser not support html5 canvas tag.</canvas> </body> </html>

javascript:

function drawprofile(ctx,x,y,width,height) {     this.flp = false;     this.x = function(r){ return math.floor(width*(this.flp?1-r:r)); }     this.y = function(r){ return math.floor(height*r); }      ctx.save();      ctx.translate( x, y );     ctx.fillstyle="#40ff00";      ctx.beginpath();     ctx.moveto( this.x(0), this.y(1) );     ctx.beziercurveto(         this.x(0),      this.y(125/190),         this.x(70/190), this.y(170/190),         this.x(75/190), this.y(120/190)     );     ctx.lineto( this.x(95/190), this.y(130/190) );     ctx.beziercurveto(         this.x(40/190), this.y(130/190),         this.x(30/190), this.y(0),          this.x(95/190), this.y(0)     );      this.flp = true;      ctx.beziercurveto(         this.x(30/190), this.y(0),         this.x(40/190), this.y(130/190),          this.x(95/190), this.y(130/190)     );     ctx.lineto( this.x(75/190), this.y(120/190) );     ctx.beziercurveto(         this.x(70/190), this.y(170/190),         this.x(0), this.y(125/190),         this.x(0), this.y(1)     );     ctx.fill();      this.flp = false;      ctx.restore(); }  function drawstar(ctx,x,y,height) {      var pnts = 5,         rad = height/(1-math.cos(0.8*math.pi));      this.x = function(p,dst){         return dst * math.sin( (p/pnts)*2*math.pi );     }     this.y = function(p,dst){         return dst * math.cos( (p/pnts)*2*math.pi ) * -1;     }     this.movepct = function(a,b,pct){         var f = (function(x){                 var m = (b.y-a.y)/(b.x-a.x);                 return m*x+(a.y-(a.x*m));             }).bind(),             r = b.x - a.x,             point = {};          point.x = a.x+(r*pct);         point.y = f(point.x);          return point;     }     this.transpoints = function(s,p,e,pct){         var sp = this.movepct(s,p,pct),             ep = this.movepct(e,p,pct);          return [sp,ep];     }      ctx.save();      ctx.translate( x+rad, y+rad );     ctx.fillstyle = "#ffff00";      ctx.beginpath();      for(var i=0;i<pnts;i++){         var dst = rad/2,             s = { x: this.x( i+0.5, dst ),                   y: this.y( i+0.5, dst ) },             p = { x: this.x( i+1, rad ),                   y: this.y( i+1, rad ) },             e = { x: this.x( i+1.5, dst ),                   y: this.y( i+1.5, dst ) },             t = this.transpoints(s,p,e,.75);          if(i==0){ ctx.moveto( s.x, s.y ); }          ctx.lineto(t[0].x, t[0].y);         ctx.quadraticcurveto(p.x, p.y, t[1].x, t[1].y);         ctx.lineto(e.x, e.y);     }     ctx.fill();      ctx.restore();  }  function draw(c) {      var ctx = c.getcontext("2d");      this.x = function(r){ return c.width*r; }     this.y = function(r){ return c.height*r; }      ctx.shadowblur=this.y(1/19);     ctx.shadowcolor="black";      //drawstar( ctx, this.x(-3/19), this.y(-1/19), this.y(20/19) );     drawprofile( ctx, this.x(6/19), this.y(1/19), this.x(18/19), this.y(18/19) );       if(0){         ctx.clearrect( this.x(1), this.y(0), this.x(1), this.y(1) );         ctx.clearrect( this.x(0), this.y(1), this.x(1), this.y(1) );     }  }  draw( document.getelementbyid("mycanvas") );

you're using this in functions. in context here, this bound window (there lots of resources out there how use this, , you're doing incorrectly).

in each function use this, is bound same thing (window) over-write each other's variables. (this because of way you're using functions. if newed them different story).

so

  1. your draw() method sets this.x, window.x,
  2. then passes drawstar() argument
  3. the drawstar() function method changes value of this.x (which window.x) , returns draw()
  4. then draw() calls drawprofile() this.x (which window.x), except time value function rather float value wanted be.
  5. drawprofile expected argument float, it's function

(for x read x , y)

you can closures , variables. remove thises , program work. probably.


Comments

Post a Comment

Popular posts from this blog

html - How to style widget with post count different than without post count -

i have border below li elements in wordpress widget types appropriate. element inside set block gives them nice easy click full width. the problem, when choose option "show post count" when adding widget such categories or archives displays post count plain text after tag , because tag block pushes post number text line below. whether choose show post count or not show post count still gives exact same element identifyer example "widget_categories". how style post count not on next line still keep links non post count list items full width? here's example on sidebar www.bbmthemes.com/themes/modular/blog-standard/ in order solve problem need remove display:block; for ul.widgets ul a , add in it's place line-height: 33px; what going achieve have same visual effect. what going lose doing links going work on text , not on "box". the other way out of find post count coming , make changes this. example change text count i
Read more

How to remove text and logo OR add Overflow on Android ActionBar using AppCompat on API 8? -

have researched death , cannot find answer. i have actionbar using appcompat. supporting api v7 (api v8 do). actionbar works api v11. api < v11 has problem of removing icon (and feature) actionbar without supplying overflow. big picture have app logo, app title, , 3 icons squidging same actionbar on low end phone. trying make room! i happy 1 of 2 solutions. either: a method of getting overflow functionality can retrieved pull down. (preferred) method of removing icon , text actionbar below current xml api 11+: <resources> <!-- base application theme api 11+. theme replaces appbasetheme res/values/styles.xml on api 11+ devices. --> <style name="appbasetheme" parent="theme.appcompat.light.darkactionbar"> <item name="android:actionbarstyle">@style/liteactionbarstyle</item> <item name="actionbarstyle">@style/liteactionbarstyle</item> </st
Read more

javascript - storing input from prompt in array and displaying the array -

i want take the inputs user prompt, store input in array, , display it. want take 10 inputs user using for loop. have tried do-while shown below. var givennames = new array(); var pattern = /[\w\d]{1,}/ig; do{ var name = prompt("enter names. letters , digits accepted!\nentering empty field stops asking",""); if(name && name.match(pattern)){givennames.push(name);} } while(name != ""); function displaynames(){ if(givennames.length > 0){ document.getelementbyid("list").innerhtml = "<span style='color:navy;font- weight:bold;'>given names are:<\/span><br><br>" + givennames.join("<br><br>"); } else { document.getelementbyid("list").innerhtml = "<span style='color:navy;font-weight:bold;'>nothing has been given!<\/span>"; } } how replace for loop? var givennames = new array();
Read more