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Groups > comp.sys.acorn.programmer > #5905

Re: Rotating a Colour-Filled Square

From Sebastian Barthel <naitsabes@freenet.de>
Newsgroups comp.sys.acorn.programmer
Subject Re: Rotating a Colour-Filled Square
Date 2019-11-14 12:20 +0000
Organization solani.org
Message-ID <qqjgq3$dkd$1@solani.org> (permalink)
References <5811cae024basura@invalid.addr.uk> <qqfdpr$n4t$1@solani.org> <58124834ffbasura@invalid.addr.uk> <58125f40fdbasura@invalid.addr.uk> <qqi40d$e0m$1@solani.org>

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Am Wed, 13 Nov 2019 23:35:41 +0000 schrieb Sebastian Barthel:

> Am Wed, 13 Nov 2019 17:05:44 +0000 schrieb Richard Ashbery:
> 
>> ... but what I'm really after is a method to overlay the existing
>> square with other successively smaller squares in alternating colours.
> 
>
> To find a point where the FILL can start in a defined way, I sorted the
> X-values and used the one on the left side (XMIN).
> The y-value wich belongs to this (XMINY) is corrected by a minimal
> absolute amount, wich sets the start of the FILL in a region
> inside the square.

This can and probably should be changed to a variant wich calculates the 
startpoint for the FILL command directly.

To find such a point You could do an

 XMIN=SIN(ANGLE)*(F-8) : XMINY=COS(ANGLE)*(F-8)
 FILL XMIN,XMINY

and delete all the other lines wich include XMIN or XMINY.

But: This starts the filling everytime on another part of the screen. 
Thats why the filling itself will then sometimes go from up to down and 
sometimes down to up and in 50% it starts on the left side and in 50% on 
the right side. I suppose its possible to see a difference between these 
variations of the fill-start. On the other hand this is so in original 
program too. I think the best way to do is to find the topmost pixel (or 
line) and start the filling there. But this depends also on how the 
filling routine works.

Since You are knowing about the fact that there are only squares involved 
eventually the better (best?) solution is to write a little fill 
procedure. This has to find the outmost points (leftmost,rightmost) for 
every line of the screen where the square should be plotted. With these 
coordinates one can draw a horizontal line. This should be done for every 
line in the square. Since drawing of a horizontal line can be much faster 
than a comlex FILL command wich needs to test every pixel this is 
eventually faster ; even if the squares are plotted in full and from the 
biggest to the smallest one.

The other thing one would include in such a demo is double-buffering. 
This can be done in BBC BASIC with an SWI wich switches between two 
alternating drawports. Its not a challenge but I can't remember the SWI 
number at the moment. It won't change the rest of the code and can be 
added afterwards with ease.


All the best,
Sebastian

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Thread

Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-12 14:05 +0000
  Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-12 23:04 +0000
    Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-14 16:24 +0000
      Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-14 19:29 +0000
        Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-15 21:26 +0000
        Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-15 22:23 +0000
          Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-15 22:31 +0000
            Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-16 14:05 +0000
              Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-16 19:47 +0000
                Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-18 20:02 +0000
          Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-16 00:39 +0000
            Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-16 12:21 +0000
              Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-17 10:04 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-17 13:50 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-17 14:19 +0000
                Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-17 14:21 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-17 15:34 +0000
                Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-17 16:25 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-18 16:17 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-18 16:55 +0000
          Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-16 11:48 +0000
            Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-16 14:21 +0000
              Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-18 20:04 +0000
                Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-19 14:48 +0000
                Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-19 20:26 +0000
                Re: Rotating a Colour-Filled Square Brian Jordan <brian.jordan9@btinternet.com> - 2019-11-19 20:39 +0000
                Re: Rotating a Colour-Filled Square Dave <dave@triffid.co.uk> - 2019-11-20 07:50 +0000
                Re: Rotating a Colour-Filled Square Alan Adams <alan@adamshome.org.uk> - 2019-11-20 11:26 +0000
            Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-16 19:27 +0000
              Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-16 23:37 +0000
      Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-14 20:47 +0000
    Re: Rotating a Colour-Filled Square druck <news@druck.org.uk> - 2019-11-14 20:44 +0000
      Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-15 13:35 +0000
        Re: Rotating a Colour-Filled Square Steve Fryatt <news@stevefryatt.org.uk> - 2019-11-16 00:32 +0000
    Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-13 12:54 +0000
      Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-13 17:05 +0000
        Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-13 23:35 +0000
          Re: Rotating a Colour-Filled Square Sebastian Barthel <naitsabes@freenet.de> - 2019-11-14 12:20 +0000
          Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-14 14:09 +0000
  Re: Rotating a Colour-Filled Square Richard Ashbery <basura@invalid.addr.uk> - 2019-11-14 15:21 +0000
  Re: Rotating a Colour-Filled Square news@sprow.co.uk - 2019-11-14 05:00 -0800

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