[SDL] Linedrawing

[Jonathan Dearborn]

Hey,

You can check out SPriG as well.  It's my up-to-date branch of SGE found here: http://pubpages.unh.edu/~jmb97

But to make your immediate search easy, here's the code from SPriG/SGE for drawing a line:

//==================================================================================
// Draws a line
//==================================================================================
void _Line(SDL_Surface *surface, Sint16 x1, Sint16 y1, Sint16 x2, Sint16 y2, Uint32 color)
{
    //if ( !clipLine(surface, &x1, &y1, &x2, &y2) )
        //return;

    Sint16 dx, dy, sdx, sdy, x, y;

    dx = x2 - x1;
    dy = y2 - y1;

    sdx = (dx < 0) ? -1 : 1;
    sdy = (dy < 0) ? -1 : 1;

    dx = sdx * dx + 1;
    dy = sdy * dy + 1;

    x = y = 0;

    Sint16 pixx = surface->format->BytesPerPixel;
    Sint16 pixy = surface->pitch;
    Uint8 *pixel = (Uint8*)surface->pixels + y1*pixy + x1*pixx;

    pixx *= sdx;
    pixy *= sdy;

    if (dx < dy)
    {
        Sint32 tmp = dx;
        dx = dy;
        dy = Sint16(tmp);
        tmp = pixx;
        pixx = pixy;
        pixy = tmp;
    }

    switch (surface->format->BytesPerPixel)
    {
    case 1:
    {
        for (x=0; x < dx; x++)
        {
            *pixel = color;

            y += dy;
            if (y >= dx)
            {
                y -= dx;
                pixel += pixy;
            }
            pixel += pixx;
        }
    }
    break;

    case 2:
    {
        for (x=0; x < dx; x++)
        {
            *(Uint16*)pixel = color;

            y += dy;
            if (y >= dx)
            {
                y -= dx;
                pixel += pixy;
            }
            pixel += pixx;
        }
    }
    break;

    case 3:
    {
        Uint8 rshift8 = surface->format->Rshift/8;
        Uint8 gshift8 = surface->format->Gshift/8;
        Uint8 bshift8 = surface->format->Bshift/8;
        Uint8 ashift8 = surface->format->Ashift/8;

        Uint8 R = (color>>surface->format->Rshift)&0xff;
        Uint8 G = (color>>surface->format->Gshift)&0xff;
        Uint8 B = (color>>surface->format->Bshift)&0xff;
        Uint8 A = (color>>surface->format->Ashift)&0xff;

        for (x=0; x < dx; x++)
        {
            *(pixel+rshift8) = R;
            *(pixel+gshift8) = G;
            *(pixel+bshift8) = B;
            *(pixel+ashift8) = A;

            y += dy;
            if (y >= dx)
            {
                y -= dx;
                pixel += pixy;
            }
            pixel += pixx;
        }
    }
    break;

    case 4:
    {
        for (x=0; x < dx; x++)
        {
            *(Uint32*)pixel = color;

            y += dy;
            if (y >= dx)
            {
                y -= dx;
                pixel += pixy;
            }
            pixel += pixx;
        }
    }
    break;
    }
}





Good luck,
Jonny D


> To: sdl at libsdl.org
> From: norbert.melzer at gmx.net
> Date: Sun, 6 Jan 2008 00:16:20 +0500
> Subject: Re: [SDL] Linedrawing
> 
> Am Sat, 5 Jan 2008 17:08:42 +0000 (UTC) schrieb Zedr0n:
> 
> > Norbert Melzer <norbert.melzer <at> gmx.net> writes:
> > 
> >> 
> >> Hi Group!
> >> 
> >> I have a problem with drawing lines. I googled a bit and found finished
> >> c-code for a Bresenham-line in the wikipedia, I adopted this code into my
> >> C++ class (original code is the same, except that that the function is
> >> embedded in a class and putpixel is now this->putpixel).
> > 
> > Any particular reason you don't want to use openGL? If not, then you
> > can just use gl functions to draw a line and be done with it :)
> 
> There is no particular reason for that, except, I didnt know that OGL can
> do that :-) On the other side, I wanted to keep requirements low. It is
> hard to justify the requirement of a state of the art PC for a turnbased
> strategy game with simple 2 dimensional linedrawings and some text...
> 
> Or is OGL not screwing requirements like this?
> 
> TIA
> Norbert
> 
> _______________________________________________
> SDL mailing list
> SDL at lists.libsdl.org
> http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

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