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

[Jason H. <jas...@bt...>]

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
>
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