raycast.cpp

//
#define ISWALL( Z, X, Y ) ((Z->data[ (X) + ((Y) * Z->width) ] & cWall ) > 0 )
#define IPART( X ) ((float)((int)(X)))

//
struct sCollideMap
{
    // map size and scale
    uint32  width, height;
    uint32  tileSize;
    // tile data encoded as above
    uint8  *data;
};

//
struct sCollideRay
{
    // ray end points
    sint32 x1, y1, x2, y2;
    // intersection location
    sint32 i_x, i_y;
};

//
bool collide_raycast
(
    sCollideMap *map,
    sCollideRay *ray
)
{
    // ---- ---- ---- ---- ---- ---- ---- ---- SETUP
    // initial location
    float ix = ((float)(ray->x1)) / (float)map->tileSize;
    float iy = ((float)(ray->y1)) / (float)map->tileSize;
    // starting positions
    float x_px = ix, x_py = iy;
    float y_px = ix, y_py = iy;
    // direction vector
    float dx = ((float)(ray->x2)) - ((float)(ray->x1));
    float dy = ((float)(ray->y2)) - ((float)(ray->y1));

    // ---- ---- ---- ---- ---- ---- ---- ---- Y AXIS INTERSECTIONS
    if ( dy > 0 )
    {
        float yp = dx / dy;
        //
        y_px += ( IPART( y_py + 1 ) - y_py ) * yp;
        y_py  =   IPART( y_py + 1 );
        for ( ;; )
        {
            //
            if ( IPART(y_py) >= map->height ) break;
            if ( IPART(y_px) <  0           ) break;
            if ( IPART(y_px) >= map->width  ) break;
            //
            if ( ISWALL( map, (int)y_px, (int)y_py ) )
                break;
            //
            y_px += yp;
            y_py  = (float)( (int)y_py + 1 );
        }
    }
    else if ( dy < 0 )
    {
        float yp = dx / dy;
        //
        y_px -= (y_py - IPART( y_py ) ) * yp;
        y_py  =         IPART( y_py );
        for ( ;; )
        {
            //
            if ( IPART(y_py-1) <  0          ) break;
            if ( IPART(y_px  ) <  0          ) break;
            if ( IPART(y_px  ) >= map->width ) break;
            //
            if ( ISWALL( map, (int)y_px, (int)(y_py-1) ) )
                break;
            //
            y_px -= yp;
            y_py  = (float)( (int)y_py - 1 );
        }
    }

    // ---- ---- ---- ---- ---- ---- ---- ---- X AXIS INTERSECTIONS
    if ( dx > 0 )
    {
        float xp = dy / dx;
        //
        x_py += ( IPART( x_px + 1 ) - x_px ) * xp;
        x_px  =   IPART( x_px+1 );
        for (;; )
        {
            //
            if ( IPART(x_px) >= map->width  ) break;
            if ( IPART(x_py) <  0           ) break;
            if ( IPART(x_py) >= map->height ) break;
            //
            if ( ISWALL( map, (int)x_px, (int)(x_py) ) )
                break;
            //
            x_px  = (float)( (int)x_px + 1 );
            x_py += xp;
        }
    }
    else if ( dx < 0 )
    {
        float xp = dy / dx;
        //
        x_py -= (x_px - IPART( x_px )) * xp;
        x_px  =         IPART( x_px );
        for ( ;; )
        {
            //
            if ( IPART(x_px-1) <  0           ) break;
            if ( IPART(x_py  ) <  0           ) break;
            if ( IPART(x_py  ) >= map->height ) break;
            //
            if ( ISWALL( map, (int)(x_px-1), (int)(x_py) ) )
                break;
            //
            x_px  = (float)( (int)x_px - 1 );
            x_py -= xp;
        }
    }

    // ---- ---- ---- ---- ---- ---- ---- ---- INTERSECTION SELECTION
    float dx1 = (x_px-ix) * (x_px-ix);
    float dy1 = (x_py-iy) * (x_py-iy);
    float dx2 = (y_px-ix) * (y_px-ix);
    float dy2 = (y_py-iy) * (y_py-iy);
    //
    if ( (dx1+dy1) < (dx2+dy2) )    msmark( x_px, x_py );
    else                msmark( y_px, y_py );
    //
    return false;
}