8BitPimp

// this code is written by Aidan Dodds 7/may/2013
// do not reuse this code in anything commercial without my permission

//
int invaderSeed = 0;

//
char invader[] =
{
    0, 1, 1, 1, 0,
    1, 0, 1, 0, 1,
    1, 0, 1, 0, 1,
    1, 1, 1, 1, 1,
    1, 0, 1, 0, 1,
};

//
uint32 g_noise = 0xDEADBABE;

//
static
inline int myRand( void )
{
    const uint32 taps = 0x80306031;
    sint32 l = g_noise;
    if (l & 0x1)    l = (1 << 31) | ((l ^ taps) >> 1);
    else            l = (l >> 1);
    g_noise = l;
    return l;
}

//
void generateInvader( void )
{
    //
    invaderSeed = g_noise;
    //
    for ( int i=0; i<5*5; i++ )
        invader[i] = 0;
    //
    for ( int y=0; y<5; y++ )
    {
        for ( int x=0; x<5; x++ )
        {
            if ( x < 3 )
            {
                // left side randomness
                invader[ x + y*5 ] = myRand( ) & 0x1;
            }
            else
            {
                // right side symmetry
                invader[ x + y*5 ] = invader[ (4-x) + y*5 ];
            }
        }
    }
}

//
void drawInvader( int x, int y )
{
    //
    draw_set_colour( invaderSeed );
    //
    for ( int i=0; i<5*5; i++ )
    {
        if ( invader[i] != 0 )
        {
            int tx = x + i % 5;
            int ty = y + i / 5;
            // plot a pixel
            draw_plot( tx, ty );
        }
    }
}

//
void make_all_invaders( void )
{
    draw_clear_screen( );
    //
    int x = 16;
    int y = 16;
    //
    while ( true )
    {
        generateInvader( );
        drawInvader( x, y );
        //
        if ( x + 7 > target->w - 16 )
        {
            x  = 16;
            y +=  7;
            //
            if ( y + 7 > target->h - 16 )
                break;
        }
        else
            //
            x += 7;
    }
}