BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Help with Arc needed          BorlandTalk.com Forum Index -> comp.lang.pascal.delphi.misc View previous topic :: View next topic   Author Message Roy Guest Posted: Tue Jan 27, 2004 1:23 pm    Post subject: Help with Arc needed Hi, I thought I'd posted this before but can find no reference to it. I've gone daft trying to get the TCanvas.Arc proc to draw an arc from 0-360 based on the value of a slider (min=0 max=360) and was really REALLY hoping someone out there could help. The effect I'm looking for is much like those funky car RPM indicators. Any takers? Thanks, Roy. Back to top David C. Ullrich Guest Posted: Tue Jan 27, 2004 2:51 pm    Post subject: Re: Help with Arc needed On Tue, 27 Jan 2004 13:23:15 -0000, "Roy" <roy (AT) mechnet (DOT) liv.ac.uk> wrote: Quote: Hi, I thought I'd posted this before but can find no reference to it. I've gone daft trying to get the TCanvas.Arc proc to draw an arc from 0-360 based on the value of a slider (min=0 max=360) and was really REALLY hoping someone out there could help. Well, you really don't say exactly where you want to draw the arc... This may get you started: procedure DrawArc(Target: TCanvas; centerX, centerY, radius: integer; startangle, endangle: double); //angles are in radians, just to leave you something to figure out... var x1, y1, x2, y2, x3, y3, x4, y4: integer; begin x1:= centerX - radius; y1:= centerY - radius; x2:= centerX + radius; y2:= centerY + radius; x3:= centerX + round(radius*Cos(startangle)); y3:= centerY - round(radius*Sin(startangle)); x4:= centerX + round(radius*Cos(endangle)); y4:= centerY - round(radius*Sin(endangle)); Target.Arc(x1, y1, x2, y2, x3, y3, x4, y4); end; procedure TForm1.Button1Click(Sender: TObject); begin DrawArc(Canvas, 100, 100, 50, Pi/4, Pi); end; Quote: The effect I'm looking for is much like those funky car RPM indicators. Any takers? Thanks, Roy. ************************ David C. Ullrich Back to top Rob Kennedy Guest Posted: Tue Jan 27, 2004 4:36 pm    Post subject: Re: Help with Arc needed Roy wrote: Quote: Hi, I thought I'd posted this before but can find no reference to it. http://groups.google.com/groups?q=arc+author:roy&scoring=d Trouble use TCanvas.Arc http://groups.google.com/groups?th=d0b60e9fa2f442c6 -- Rob Back to top AlanGLLoyd Guest Posted: Tue Jan 27, 2004 4:58 pm    Post subject: Re: Help with Arc needed I gave the following reply on 16 Jan 2004 to a posting entitled "Trouble use TCanvas.Arc" ... = = = = = = = = = = = = = = = = = = = = = = = = = = = = "In article <bu97kd$5j3$1 (AT) news (DOT) liv.ac.uk>, "Roy" <roy (AT) mechnet (DOT) liv.ac.uk> writes: Quote: I want to use the arc procedure to draw an arc from 0 to 360 degrees, say using a simple slider. procedure Arc(X1, Y1, X2, Y2, X3, Y3, X4, Y4: Integer); The first four parameters define the bounding rectangle for the ellipse or circle. If we assume definition from top-left to bottom-right, then X1,Y1 is the top-left point of the rectangle, X2,Y2 is the bottom-right point. For a circle this would define the opposite diagonal corners of a square. A circle will have X2 - X1 == Y2 - Y1, and the circle will be drawn _within_ that square rectangle, touching the sides at their midpoints. Now comes the obscure bit. X3,Y3 and X4,Y4 define points _outside_ the circle. You know where the centre of the circle is in the middle of the square rectangle. Imagine a line drawn from X3,Y3 point to the centre of the circle. Imagine another line drawn from the X4,Y4 point also to the centre of the circle. Note the place where the line from X3, Y3 to the circle's centre, crosses the circle. Call this place A. Note the place where the line from X4, Y4 to the circle's centre, crosses the circle. Call this place B. Starting at place A on the circle, move counter-clockwise (opposite rotation to a clock) towards and up to place B. This is the arc which TCanvas.Arc will draw. So an arc from 12 o'clock to 9 o'clock on a 50 dia circle centred at 200, 100 would have an arc definition (I think <g>) of ... Arc(175, 75, 225, 125, 150, 100, 200, 50); The same (but with slightly more conceptual difficulty) applies to an ellipse. If you want to have a rotating slider then you will have to calculate the positions of X3, Y3 and X4, Y4 using the Sin and Cos of the equivalent (or actual) angle of your slider and a radius greater than that of the circle. When you have mastered this (preferably with a piece of graph paper and a pencil), then move on to TCanvas.Chord and TCanvas.Pie <g>." = = = = = = = = = = = = = = = = = = = = = = = = is it "Good job I keep what I posted" or "No-one reads what I write" <g> Welcome back David C. Ullrich <g>. Alan Lloyd [email]alanglloyd (AT) aol (DOT) com[/email] Back to top Roy Guest Posted: Wed Jan 28, 2004 10:21 am    Post subject: Re: Help with Arc needed Thanks a million guys - not only does the code snippet (now much modified) solve my problem, but with Alan's tutorial it all makes sense too! In case you're interested, the code is part of the instrumentation for this: http://www.jetstream-club.org a rare project! Thanks again. Roy. Back to top David C. Ullrich Guest Posted: Wed Jan 28, 2004 11:48 am    Post subject: Re: Help with Arc needed On 27 Jan 2004 16:58:51 GMT, [email]alanglloyd (AT) aol (DOT) com[/email] (AlanGLLoyd) wrote: Quote: [...] Welcome back David C. Ullrich <g>. Thanks. Won't be staying long, doing other things. Since I got a little help the other day (and may be asking for a little more soon) I thought I should contribute a little, and this seemed like a reasonable place to do that, given my degree in trigonometry and all... Quote: Alan Lloyd [email]alanglloyd (AT) aol (DOT) com[/email] ************************ David C. Ullrich Back to top AlanGLLoyd Guest Posted: Wed Jan 28, 2004 2:55 pm    Post subject: Re: Help with Arc needed In article <bv82f3$98a$1 (AT) news (DOT) liv.ac.uk>, "Roy" <roy (AT) mechnet (DOT) liv.ac.uk> writes: Quote: but with Alan's tutorial it all makes sense too! Perhaps it might be useful on the FAQ (Maarten ?), although I have not seen this question frequently asked. But I must admit to a little head-scratching and pencil-on-paper when I first saw it <g>. Possibly it should be an Annotation for each individual's help file. Perhaps we ought to start an "Explanation" area on the FAQ site where individual chunks of text are available for people to copy and add to their help files as annotations if they wish. Alan Lloyd [email]alanglloyd (AT) aol (DOT) com[/email] Back to top Dodgy Guest Posted: Wed Jan 28, 2004 4:29 pm    Post subject: Re: Help with Arc needed On Wed, 28 Jan 2004 10:21:21 -0000, "Roy" <roy (AT) mechnet (DOT) liv.ac.uk> waffled on about something: Quote: Thanks a million guys - not only does the code snippet (now much modified) solve my problem, but with Alan's tutorial it all makes sense too! In case you're interested, the code is part of the instrumentation for this: http://www.jetstream-club.org a rare project! Very interesting... Just don't forget to connect the throttles! I hope there's going to be a "Powered by Delphi" paint job. ) Dodgy. -- MUSHROOMS ARE THE OPIATE OF THE MOOSES Back to top Dr John Stockton Guest Posted: Wed Jan 28, 2004 8:04 pm    Post subject: Re: Help with Arc needed JRS: In article <20040128095540.07155.00000325 (AT) mb-m06 (DOT) aol.com>, seen in news:comp.lang.pascal.delphi.misc, AlanGLLoyd <alanglloyd (AT) aol (DOT) com> posted at Wed, 28 Jan 2004 14:55:40 :- Quote: Perhaps it might be useful on the FAQ (Maarten ?), although I have not seen this question frequently asked. But I must admit to a little head-scratching and pencil-on-paper when I first saw it <g>. Presumably Arc was chosen as being a powerful primitive in <= TP4 days. I was about to suggest that a Delphi library should be available that builds on Arc to give Ellipse & Circle, etc.; then I saw that TP4 has those, so Delphi should; but what Delphi has differs. There is also Pie & PieSlice. ISTM that it would still be useful to have such a library, with easily- understood names and handy parameters, implemented by the primitives. The body of Circle(X, Y, R) might just be Ellipse(X-R, Y-R, X+R, Y+R) - which is not necessarily obvious to all. There could be Conic for more general shapes, and a Wodge more like Pascal than Delphi. -- © John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Delphi 3 Turnpike 4 © <URL:http://www.bancoems.com/CompLangPascalDelphiMisc-MiniFAQ.htm> clpdmFAQ; <URL:http://www.borland.com/newsgroups/guide.html> news:borland.* Guidelines Back to top Maarten Wiltink Guest Posted: Wed Jan 28, 2004 9:38 pm    Post subject: Re: Help with Arc needed "AlanGLLoyd" <alanglloyd (AT) aol (DOT) com> wrote Quote: In article <bv82f3$98a$1 (AT) news (DOT) liv.ac.uk>, "Roy" <roy (AT) mechnet (DOT) liv.ac.uk writes: Quote: but with Alan's tutorial it all makes sense too! Perhaps it might be useful on the FAQ (Maarten ?), although I have not seen this question frequently asked. But I must admit to a little head-scratching and pencil-on-paper when I first saw it Not a chance. It's not frequently asked and what's more, it's a FAQ and *not* a tutorial collection. It's my stated policy to be strict about that distinction. Quote: Possibly it should be an Annotation for each individual's help file. Perhaps we ought to start an "Explanation" area on the FAQ site where individual chunks of text are available for people to copy and add to their help files as annotations if they wish. A tutorial collection associated with the miniFAQ would be nice to have, because there is demand for it - or rather, supply to which we do want to point people. But it would be rather a lot of work and I'm not about to volunteer for doing an entire collection next to the miniFAQ. I have one or two attempts on my own website and that was quite humbling enough, thank you. Groetjes, Maarten Wiltink / Evil miniFAQ Boss Back to top AlanGLLoyd Guest Posted: Thu Jan 29, 2004 6:15 am    Post subject: Re: Help with Arc needed In article <40182bc3$0$327$e4fe514c (AT) news (DOT) xs4all.nl>, "Maarten Wiltink" <maarten (AT) kittensandcats (DOT) net> writes: Quote: A tutorial collection associated with the miniFAQ would be nice to have, because there is demand for it - or rather, supply to which we do want to point people. But it would be rather a lot of work and I'm not about to volunteer for doing an entire collection next to the miniFAQ. I have one or two attempts on my own website and that was quite humbling enough, thank you. Do you mean a tutorial for any FAQ in the list, or a general one for a repository when a possible candidate turned up. I was not suggesting an "all-out effort to construct an edifice" but rather a "pit where we throw bricks as they turn up". Would providing such a "pit" be a big exercise. Alan Lloyd [email]alanglloyd (AT) aol (DOT) com[/email] Back to top Jeremy Collins Guest Posted: Thu Jan 29, 2004 8:10 am    Post subject: Re: Help with Arc needed AlanGLLoyd wrote: Quote: Do you mean a tutorial for any FAQ in the list, or a general one for a repository when a possible candidate turned up. I was not suggesting an "all-out effort to construct an edifice" but rather a "pit where we throw bricks as they turn up". Would providing such a "pit" be a big exercise. I think Borland's CodeCentral already does this, have you thought about submitting your Arc example? -- jc Remove the -not from email Back to top Jeremy Collins Guest Posted: Thu Jan 29, 2004 8:12 am    Post subject: Re: Help with Arc needed Dodgy wrote: Quote: Very interesting... Just don't forget to connect the throttles! I hope there's going to be a "Powered by Delphi" paint job. ) I'd forgotten about this: http://tinyurl.com/2rqmn -- jc Remove the -not from email Back to top Maarten Wiltink Guest Posted: Thu Jan 29, 2004 6:47 pm    Post subject: Re: Help with Arc needed "AlanGLLoyd" <alanglloyd (AT) aol (DOT) com> wrote [...] Quote: I was not suggesting an "all-out effort to construct an edifice" but rather a "pit where we throw bricks as they turn up". Would providing such a "pit" be a big exercise. No. Yes. It depends. The bottom line remains: what would be the added value? Everybody who writes a tutorial can publish it on her own website, or submit it to any number of brick pits. I'll be happy to accept hyperlinks in either category for the miniFAQ. Because the question is not if tutorials would fit in nicely with the idea of the miniFAQ; they would. The question is if we should duplicate other efforts, and if we could beat them at it, and if we should even try (either the duplication or the beating). 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