Does anyone have a C code to graph some antialiased lines?

[Anaxetus]

Antialiased lines

Does anyone has a good C code to graph some "antialiased" lines. That is lines with some dither arround (like in an analog scope).
It is intended to be used in PC programming enviroment.

Regards,

 

[mik27]

Re: Antialiased lines

Try this ...

I assume that:

The color (r, g, b) are float in [0, 1] space (you can easy change it in to [0,255])
VideoBuffer is a 'unsigned char *' (unsigned char pointer) to RGB 8/8/8 = 24bit video buffer
VideoDimX, VideoDimY is the resolution X and Y of VideoBuffer

void WritePixel(const int x,const int y, 
const float r, const float g, const float b, const float alpha)
{

    //3 is for RGB 24bit deepth
    unsigned char* pVideo=VideoBuffer+(x+(VideoDimX-(y+1))*VideoDimY)*3; 
    pVideo[0]=(alpha*r)*255+(1.0f-alpha)*pVideo[0];
    pVideo[1]=(alpha*g)*255+(1.0f-alpha)*pVideo[1];
    pVideo[2]=(alpha*b)*255+(1.0f-alpha)*pVideo[2];
}

void LineAA(const int x1,const int y1,const int x2,const int const y2,
                     const float r,const float  g, const float b)
{
    // useful constants
    const float dw=x2-x1;
    const float dh=y2-y1;
    const float slx=dh/dw;
    const float sly=dw/dh;

    // determine the slope
    if(fabs(slx)<1.0)
    {
        // x scan
        int tx1=x1;
        int tx2=x2;
        float raster=y1;

        if(x1>x2)
        {
            tx1=x2;
            tx2=x1;
            raster=y2;
        }

        for(int x=tx1;x<=tx2;x++)
        {
            const int ri=int(raster);

            const float AlphaY0=1.0-(raster-ri);
            const float AlphaY1=1.0-(ri+1-raster);

            WritePixel(x,ri  ,r,g,b,AlphaY0);
            WritePixel(x,ri+1,r,g,b,AlphaY1);

            raster+=slx;
        }
    }
    else
    {
        // y scan
        int ty1=y1;
        int ty2=y2;
        float raster=x1;

        if(y1>y2)
        {
            ty1=y2;
            ty2=y1;
            raster=x2;
        }

        for(int y=ty1;y<=ty2;y++)
        {
            const int ri=int(raster);

            const float AlphaX0=1.0-(raster-ri);
            const float AlphaX1=1.0-(ri+1-raster);

            WritePixel(ri  ,y,r,g,b,AlphaX0);
            WritePixel(ri+1,y,r,g,b,AlphaX1);

            raster+=sly;
        }
    }
}

I have made some modifications in order to generalize the algorithm and to render it more readable (is not optimized!) ... but, after, I have not tried it ... tell me if you have any problem

regards ... M!k27

 

[mik27]

Re: Antialiased lines

Another thing ... I remember that I had written it for a reverse Y VideoBuffer (like Windows DIB ... left -> right, DOWN -> UP) ... for a 'standard' frame VideoBuffer with the origin in left top corner (left -> right, up -> down) you must change the line in the previous code ...

unsigned char* pVideo=VideoBuffer+(x+(VideoDimX-(y+1))*VideoDimY)*3;

in the line ...

unsigned char* pVideo=VideoBuffer+(y*VideoDimX+x)*3;

bye ... m!k27