220 19169 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Point class Date: Wed, 22 Jul 2015 14:24:06 -0400 Lines: 53 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1437589469 31223 80.91.229.3 (22 Jul 2015 18:24:29 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 22 Jul 2015 18:24:29 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBUF7X6WQKGQECRBHMUQ@isocpp.org Wed Jul 22 20:24:20 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f199.google.com ([209.85.217.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZHygj-00087E-P1 for gclcip-std-proposals@m.gmane.org; Wed, 22 Jul 2015 20:24:17 +0200 Original-Received: by lbcjf8 with SMTP id jf8sf59741986lbc.0 for ; Wed, 22 Jul 2015 11:24:17 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:content-type:user-agent:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=eGzLcvQM/sML0KpJvD9V6aU9kbgQExm6SvRh64ygr4Q=; b=ArD6BJ7OdB5qiHoPH0yEK1i01KQTasZFeZYJbnR0KpRq7FIuwU8sBd/nzL4E6YrNho HvFiSQU2XpiXj8DHBlmOcFihoHrEX6Zr9m2NCyfNUomPZPidBftvVTu5vn8LmJLqKIuO IT5IDuSiwnZxzqtKZiNGlkSvOHpGbc1CGOKFae0NDveZ5dHTKKcyO9SRtXOUjwWrLo51 soYhJVSYkO5p9+YffywjnkEGDo3UpTkm6ugq4SIwWIXovIA5Zxi5zim+50e5738g0v3q 4D+HULT7PnVdfGesgt3JMaY/tv/ZI+KLGuH1ratmHl9Ws+V6xJi63zvRMc6+S2ccXvw7 X-Gm-Message-State: ALoCoQlnqBN/AQsAyKOW+6ZuZITs25RumP0g3FPduWYLkKnYEJmS6VK4h8QMRwA1jrKTVcmzOyqa X-Received: by 10.180.106.10 with SMTP id gq10mr12120615wib.0.1437589457088; Wed, 22 Jul 2015 11:24:17 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.28.100 with SMTP id a4ls141195lah.52.gmail; Wed, 22 Jul 2015 11:24:15 -0700 (PDT) X-Received: by 10.152.21.103 with SMTP id u7mr3543564lae.49.1437589455171; Wed, 22 Jul 2015 11:24:15 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id rc5si1837152lac.166.2015.07.22.11.24.15 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 22 Jul 2015 11:24:15 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZHyge-00085v-36 for std-proposals@isocpp.org; Wed, 22 Jul 2015 20:24:12 +0200 Original-Received: from tripoint.kitware.com ([66.194.253.20]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 22 Jul 2015 20:24:12 +0200 Original-Received: from mwoehlke.floss by tripoint.kitware.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 22 Jul 2015 20:24:12 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 44 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: tripoint.kitware.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org; dmarc=fail (p=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:19169 Archived-At: On 2015-07-22 13:46, David Haim wrote: > yes, every vector can be built from the origin to some point, thus any > point can represent a vector (starting from the origin) and vice-versa. > a point is definitely not a vector, and a vector is not a point. saying > that one is redundant is not mathematically right. Maybe not, but from a programming standpoint this is a *semantic* difference. You will find many instances of geometry libraries that have a "vector" type that is used interchangeably for both entities. GLSL, to name a big one. (That said, I bet I could find mathematicians that would say that a point *is* a vector... at least in a linear algebra sense, if not a geometry sense.) > plus, let's say in the future we want to implement a "Rectangle" or > "Circle" shape, I don't see how mathematically speaking a rectangle is > composed from 4 vectors. It is composed from 4 points. I have a CAD suite I've been working on (off and on) for ages that uses Eigen for the low level geometry classes. All point locations are given as Eigen::Vector3D. I don't even have typedefs to semantically separate "actual" vectors from points. > but if you insist that a point is a vector , you are recognizing the vast > utilities a Point can have: the entire linear algebra and the virtual > graphics use it as key feature. this is exactly why C++ has to standardize > it. I think you meant "utilities a Vector can have", but yes, that's exactly my point; a well-featured vector type can do everything a point type can, plus a LOT more. Really, what you want isn't a point type, it's an N-dimensional array of numbers that supports various linear algebra operations. And really, that's all a "vector" is in the linear algebra sense; it's usage in a geometry context that supplies more specific semantics. That's going to be far more widely useful than something restricted to the semantics of a geometry "point". Oh, and, it should also be a subclass of std::array :-). -- Matthew -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .