Re: [Dev-C++] Drawing Lines...

[St0fF 6. <st...@gm...>]

Thanks to Jason for explaining Bresenham's algorithm.  I'm sure Dx Fx needs
to get to know about some pretty nice helpers: Books and search engines.
Hunting with a goot search engine on '+drawing +lines' would probably have
been enough ...

St0fF.

----- Original Message -----
From: "Jason Hardman" <jas...@bt...>
To: "Dev-C++" <dev...@li...>; "<Dx 8a>"
<vin...@ed...>
Sent: Sunday, November 04, 2001 3:26 AM
Subject: Re: [Dev-C++] Drawing Lines...


> Hello! Me again. Probably sick of me replying all the time and not being
> helpful enough.
>
> I'm not sure of your level of maths knowledge, but I'll put it simply and
> elaborate later (if you want). There are algorithms for drawing lines that
> are optimised for speed and can do things like anti-aliasing, but to do a
> simple line with simple maths then all you need to know is how to
calculate
> the gradient of the line.
>
> If I had a pen and paper and could explain it that way it would be easier,
> but I'll try in writing.
>
> By calculating the gradient you can then tell how much y increases (or
> decreases) for each one of x (or x of y) i.e.
> Assuming x1 (start) is smaller than x2 (end), i.e. line going left to
right
> on a screen. If not the case just swap coords around.
>
> double gradient, dx, dy, x, y;
>
> dx = x1 - x2; // change in x
> dy = y1 - y2; // change in y
>
> gradient = dy/dx;
>
> for(x = x1, y = y1; x <= x2; ++x, y += gradient)
>     putpixel(static_cast<int>(x), static_cast<int>(y), colour);
> /* proper rounding would be better, but simple rounding down of decimals
in
> double to int conversion should be OK */
>
> This is a guide of what you might do. I've not tested it, but AFAICT the
> math is OK. With a little more work you should be able to go in any
> direction. Other algorithms avoid the use of floating point representation
> cos it's slower than integer maths.
>
> I'll go into putpixel later if you want, but first can I ask what are you
> trying to do (apart from draw a line)? If you are working in a window then
> there are a broad set of drawing functions available for use, i.e.
LineTo(),
> Polygon(), Rectangle() etc... and they can be used on a DirectX app if
need
> be? I hope I'm not confusing the issue?
>
> Jason.
>
> ----- Original Message -----
> From: "<Dx 8a>" <vin...@ed...>
> To: "Dev-C++ mailing list" <dev...@li...>
> Sent: Sunday, November 04, 2001 1:31 AM
> Subject: [Dev-C++] Drawing Lines...
>
>
> > Ok guys, I'll put it all together, and hopefully I can get the point...
> >
> > Using a library might be a good choice... I'tll save me a lot of time
and
> effort... But I surely don't know where I can get from so I guess I'll
have
> to do things manually.
> >
> > And yes, I think, DirectX doesn't supply a PutPixel or something to put
> points on the screen... That's why Ill have to make my own functions...
> >
> > Also, there must be someway of doing this thing mathematically... I
found
> that on a tutorial... that drawing pixels in the screen can be done
> mathematically... although, the tutorial didn't included a formula in
> drawing a straight line on the screen... Does anyone know of such a
formula?
> >
> > Drawing the pixel on the screen would require me to access the memory
> buffer or something... Ill have to make a function to simplify the task
and
> do a PutPixel...
> >
> > am I missing something? I hope I got it right, ive actually started
coding
> a few days earlier... and caused my system to crash... the reason I don't
> really know... but it sure wasn't the programming I did... which also
> prevented me to check the mailing list...
> >
> > Well guys, thanks in many ways... although I'll leave the still
unanswered
> question...
> >
> >
> >
> >
> > How do I draw Straight lines on the screen? (using DirectX)
> >
> >
> > Specifically, now Im asking of a formula that would make it sure that
what
> I'm drawing is a straight line... the previous things in the mailing list
> have actually helped me to know what Ill actually have to do In doing the
> drawing... Well... i hope someone could enlighten me somehow
> >
> > Thanks...
> >
> > Dx Fx
> >
> > __________________________________
> > www.edsamail.com
> >
> > _______________________________________________
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>
>
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