canvas - Backface removal for Perspective Projection -


i'm working on 3d exercise, , have implemented backface removal technique works orthographic projection , need change support other projections well.

what did far :

  1. for each polygon loop vertices
  2. perform transitions , projections calculations
  3. calculate surface normal newell's method
  4. draw polygon if vector direction < 0

as said works orthographic projection , i'm struggling other projections. please great

by way have seen explanation here somewhere didn't understand : "..the usual approach, used in actual 3d hardware, first of transformation (including projection), check whether resulting 2d triangle counterclockwise or clockwise wound, , keep or discard based on condition". maybe how can explain resulting 2d triangle ?

i'm using html5 canvas , js.

this approach in 3d hardware calls graphic pipeline. doesn't matter type of projections use, transformed 2d triangle , backface culling test performed.

function triangle (a, b, c) {     this.pointa = a;     this.pointb = b;     this.pointc = c; }  triangle.prototype.isbackface = function () {     var ax = this.pointa.getprojectedx() - this.pointb.getprojectedx();     var ay = this.pointa.getprojectedy() - this.pointb.getprojectedy();     var bx = this.pointa.getprojectedx() - this.pointc.getprojectedx();     var = this.pointa.getprojectedy() - this.pointc.getprojectedy();     var cz = ax * - ay * bx;     return cz < 0; };  // before drawing triangle call isbackface method. method check // either triangle counterclockwise or clockwise after  // projections. triangle.prototype.draw = function (context) {     if (this.isbackface()) {         return;     }     this._draw(); };

Comments

Post a Comment

Popular posts from this blog

javascript - jQuery: Add class depending on URL in the best way -

i have html progress meter: <div class="col-md-3" style="margin-left: -20px;"> <div class="progress-pos active" id="progess-1"> <div class="progress-pos-inner"> login </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-2"> <div class="progress-pos-inner"> scan items </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-3"> <div class="progress-pos-inner"> confirm address </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-4"> <div class="progress-pos-in
Read more

caching - How to check if a url path exists in the service worker cache -

i need check if particular url path exists in service worker cache. example, suppose url is: /myserviceworker/service?a=110&b=70 this url exists in cache, there many of them different values of , b. now, suppose want refresh of these urls, how can that? i want know how access key values service worker cache. if know key, plan follows: var url = new url(key); if(url.pathname === "\/myserviceworker/service") refetch key but not sure how cache key , in format is. mean, string or url? cache api has match() method returns promise resolving in response object if match or undefined if no match exists. second parameter object can specify ignoresearch not take account url parameters. the ignoresearch option supported firefox ( chrome status here ). in other hand, retrieve cache entries, can use keys() method.
Read more

Redirect to a HTTPS version using .htaccess -

i need modify .htaccess file redirect urls https version without "www". http://example.com --> https://example.com http://www.example.com --> https://example.com https://www.example.com --> https://example.com this how .htaccess file looks like: rewriteengine on rewritecond %{request_filename} !-d rewritecond %{request_filename} !-f rewriterule ^(.*)$ redirect.php?id=$1&page=$2 [qsa,l] what modifications need make .htaccess in order forward https without "www"? it depends on doing current code. looks file called redirect trying display php page seo friendly url. think might confusing people. anyway, need , force https without www, need 1 more rule above. also second rule needs two capture groups in rewriterule test string because wanting 2 different values using $1 , $2 references. rewriteengine on #rediect www non www and/or http https --- combinations. rewritecond %{http_host} !^example\.com [nc,or] rewritecond %{https} !^
Read more