[A89] Re: filling ellipses

To: assembly-89@lists.ticalc.org
Subject: [A89] Re: filling ellipses
From: jeff <jefromi42@yahoo.com>
Date: Sat, 7 Jul 2001 15:04:19 -0700 (PDT)
In-Reply-To: <000901c1072f$c74f39c0$f302e0c7@athlon600>
Reply-To: assembly-89@lists.ticalc.org


This is kinda what I was thinking about.  A question, though: how do you XOR the VS onto the
LCD_MEM?  (I've never tried anything with a VS before)
jeffrey

> First, use HeapAlloc() to reserve a chunk of memory the same size as the LCD
> memory (240/8*128 bytes, IIRC).  Then use PortSet() to redirect the TIOS
> routines to draw to this new "virtual screen" (VS for short).  Clear the VS.
> The use the TIOS ellipse routine to draw your ellipse on the VS, using solid
> black (not XOR).
> 
> Then you can use a very simple routine to fill the ellipse.  Start at the
> top row, and repeat for each row through the bottom row.  Scan from
> left-to-right to find the leftmost set pixel, then scan from right-to-left
> to find the rightmost set pixel.  Draw a solid black line (again, black, not
> XOR) connecting these two pixels, then move on to the next row.  (Make sure
> that it doesn't screw up on blank rows, though.)
> 
> When this is done, the VS will should your filled ellipse, in solid black,
> on an otherwise clear white screen.  Now simply XOR the VS with normal LCD
> memory, and your filled ellipse will have been XOR'd onto the screen!
> Afterwards, be sure to use HeapFree() and PortRestore().
> 
> If you want to draw a solid black ellipse to the screen, simply repeat this
> procedure but OR it onto the screen instead of XOR'ing.  If you want a solid
> white ellipse, get the filled ellipse in the VS, then invert it (by XOR'ing
> every byte of the VS with 0xFF), and then AND it onto the screen.


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References:

[A89] Re: filling ellipses

From: "Scott Noveck" <noveck@pluto.njcc.com>