From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Alp Aker Newsgroups: gmane.emacs.devel Subject: Re: Image transformations Date: Thu, 13 Jun 2019 11:57:34 -0400 Message-ID: References: <9A21DE14-BB5F-426E-BBB2-19C87930E733@gnu.org> <20190611200233.GA80199@breton.holly.idiocy.org> <83imta95z0.fsf@gnu.org> <20190612220746.GA89208@breton.holly.idiocy.org> <835zpa11qp.fsf@gnu.org> <83pnnhzlcp.fsf@gnu.org> Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="0000000000004a1128058b369723" Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="269798"; mail-complaints-to="usenet@blaine.gmane.org" Cc: Alan Third , Emacs devel To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Jun 13 19:47:05 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1hbToV-0017v2-S5 for ged-emacs-devel@m.gmane.org; Thu, 13 Jun 2019 19:47:03 +0200 Original-Received: from localhost ([::1]:42764 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hbToU-0000w9-5u for ged-emacs-devel@m.gmane.org; Thu, 13 Jun 2019 13:47:02 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:41286) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hbS73-0003Sz-0h for emacs-devel@gnu.org; Thu, 13 Jun 2019 11:58:06 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hbS70-0000nC-WE for emacs-devel@gnu.org; Thu, 13 Jun 2019 11:58:04 -0400 Original-Received: from mail-vk1-xa2d.google.com ([2607:f8b0:4864:20::a2d]:34937) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1hbS6r-0000JT-DM; Thu, 13 Jun 2019 11:57:53 -0400 Original-Received: by mail-vk1-xa2d.google.com with SMTP id k1so2057109vkb.2; Thu, 13 Jun 2019 08:57:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=p5LZhFcU/1OKcWIT+68JCpgwbY0FpA6W79XAvKY/AQc=; b=mTjkjdeCOlJqH5Hk5bEtOfqIwC+8GrvzT7+L+0i1jiO4g9KW3ZTinFRaYV6xma3M7u HzTuGZtLeAzbePB+KiY3x0Cp837m0kW61l4ztKujui0tgSnP5rPdffNYVO5at9bj3xM4 jaIhPRAwtZHnFvwSIMGbRRj6fPAR1jQbMb0VQo6ZwQlkKYvsWeumyoK4XZKNYUjAWvRK 16GEP/0WNv6vPyyoGHJZZsL3eF+jZyfFIrAFBcnSAPrPHZ6uRZ+2Ad5155bgBn/yb28y EM4m+fC/t0pPrl8CguBVvBPhWCEZzzugVjceFmNPbLjpMWfrDz8P3VTKyXpkX4lIW+cv jR5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=p5LZhFcU/1OKcWIT+68JCpgwbY0FpA6W79XAvKY/AQc=; b=a9sDD7MvfrUXhqBKbB1oURr2lqnehoyMfrtR0mL7lYWvFOTvSwOqms2fu8SWkY/FPs PI0HfyyofwK6g5Aows+alf/++R9fe3MFsqXhVHDS/OeE1i69q2gQ3WeaTFDLu0ugVaW7 9bakSOTbjPybF+UWk698NQEmiZQ2ReBnlIfxXIFt5nllrhOwSsGC/umTexVbMZZP1DHL 6caWVq1OoQ0Q2xzXtVK96bdBoK4HQSkHTWloz0hApjg6b82eH6d+btm2ykHO1frkV60J xs3j1xC7z8E4s/k5EHGC1c+/0kybCLy/Z5Z05GVuXtmmAH53X5slAqL9EHa/RUi/B12h j3FA== X-Gm-Message-State: APjAAAWSy+p5auzDAb/+J2zb10hXpNHVhL3h1ElxeWNcB/PMFeC+FBpc XvkIDYWkIWnXMugyJ3AfZtQROmfe6YJd1/QSYcnUkGJf X-Google-Smtp-Source: APXvYqwbVvE8in/EYbTobdP5dqPTLS1xPe1S89kjuQ7Rf4PwE/PTZLd409BMA3Un1/Y7t2XGMXqEooAx7t9BlPCEIIo= X-Received: by 2002:a1f:2a46:: with SMTP id q67mr20378068vkq.39.1560441466260; Thu, 13 Jun 2019 08:57:46 -0700 (PDT) In-Reply-To: <83pnnhzlcp.fsf@gnu.org> X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::a2d X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:237528 Archived-At: --0000000000004a1128058b369723 Content-Type: text/plain; charset="UTF-8" On Thu, Jun 13, 2019 at 9:05 AM Eli Zaretskii wrote: > > That's right, but this is exactly what I was trying to describe. When > I wrote "translation along the X axis", I meant the original X axis, > which is unaffected by the rotation. Are you saying that my > expectations are incorrect in that interpretation of "X axis"? > [...] > Maybe that's the problem: if the rotation is counter-clockwise, then > the translation should indeed be along the Y axis. The translation doesn't depend on the rotation in any way. The general form of an affine transformation is F(x) + b, where F is a linear transformation (rotation, shear, scaling) and addition by b is translation. In the example we're discussing, F is rotation by 90 degrees and b is (0, 232) in some coordinates. F does not act on b; the rotation does not affect what the translation does; whether F is clockwise or counter-clockwise rotation, the function displaces the result of the rotation along the (original) y axis. (The single-matrix form used by the transformation code in image.c is a computational convenience; the function it expresses still has the form F(x) + b.) --0000000000004a1128058b369723 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Thu, Jun 13, 2019 at 9:05 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> That&#= 39;s right, but this is exactly what I was trying to describe.=C2=A0 When> I wrote "translation along the X axis", I meant the origin= al X axis,
> which is unaffected by the rotation.=C2=A0 Are you sayin= g that my
> expectations are incorrect in that interpretation of &quo= t;X axis"?
> [...]
> Maybe that's the problem: if the = rotation is counter-clockwise, then
> the translation should indeed b= e along the Y axis.

The translation doesn't depend on the rotati= on in any way.=C2=A0 The general form of
an affine transformation is F(x= ) + b, where F is a linear transformation
(rotation, shear, scaling) and= addition by b is translation. In the example
we're discussing, F is= rotation by 90 degrees and b is (0, 232) in some
coordinates.=C2=A0 F d= oes not act on b; the rotation does not affect what the
translation does= ; whether F is clockwise or counter-clockwise rotation, the
function dis= places the result of the rotation along the (original) y axis. =C2=A0(Thesingle-matrix form used by the transformation code in image.c is a comput= ational
convenience; the function it expresses still has the form F(x) += b.)
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