```// make the move/remove into a single separate ram array
// and just have one copy of each asteroid. use pointers to it...
// (although that stops working when we use rotation)

#define ASTEROIDS 24

void intro(void) {
static const int white_big[] = {
// 0,   0,   0,  // adjustment for corner/center!
-1, 120, 120, -1, 120,0,  -1, 120,-120, -1,0,-120,
-1,-120,-120, -1,-120,0,  -1,-120, 120, -1,0, 120,
1
};
#define XX 14
#define YY 14
// using a copy of dx,dy means that this code can be merged with
// 'Draft4' and used before the initialisation; overlaying dx and dy
// on top of the stack.
const int8_t cdx[ASTEROIDS] = {
1,1,1,1, 2,2,2,2, -1,-1,-1,-1, -2,-2,-2,-2, 1,2,-2,-1, 1,2,-2,-1
};
const int8_t cdy[ASTEROIDS] = {
-2,-1,1,2,  -2,-1,1,2,  -2,-1,1,2,  -2,-1,1,2, -2,1,1,2, -1,-2,2,1
};
int8_t dx[ASTEROIDS], dy[ASTEROIDS];
int8_t x[ASTEROIDS], y[ASTEROIDS];
#define MARGIN 20
uint8_t direction=0;
int8_t done;
int8_t base, row, tmp1;		// , tmp2, other, diffx, diffy;
//int8_t xtarget, ytarget;

for (row = 0; row < ASTEROIDS; row++) {
dx[row]=cdx[row]; dy[row]=cdy[row];
}
row=0;
{int xx,yy; // lay out the initial board position for the animation:
for (yy = 1; yy <= 8; yy++) {
if (yy != 4 && yy != 5) {
for (xx = ((yy&1)^1)+1; xx <=8; xx+=2) {x[row] = (xx-4)*2*XX-XX; y[row++] = (yy-4)*2*YY-YY;}
}
}
}

base = 0; direction = 0;
do {
// now move asteroids around invisibly and quickly
for (row = 0; row < ASTEROIDS; row++) {
// Bounce off walls? Marginally more expensive than wrapping.
tmp1 = x[row] + dx[base + row]; // overflow test
if ((dx[base + row] > 0 && x[row] > 0 && (int8_t)(tmp1+MARGIN) < 0)
|| (dx[base + row] < 0 && x[row] < 0 && (int8_t)(tmp1-MARGIN) > 0)) {
dx[base + row] = -dx[base + row]; // bounce?
}
x[row] = x[row] + dx[base + row];

tmp1 = y[row] + dy[base + row];
if ((dy[base + row] > 0 && y[row] > 0 && (int8_t)(tmp1+MARGIN) < 0)
|| (dy[base + row] < 0 && y[row] < 0 && (int8_t)(tmp1-MARGIN) > 0)) {
dy[base + row] = -dy[base + row];
}
y[row] = y[row] + dy[base + row];
}
//base ^= ASTEROIDS;
direction++;
} while (direction != 255); // change constant depending on length and complexity of animation

// reverse the movement vectors
for (tmp1 = 0; tmp1 < ASTEROIDS; tmp1++) {
dx[tmp1] = -dx[tmp1];  dy[tmp1] = -dy[tmp1];
}

// visibly unwind...
do {
direction--;
//base ^= ASTEROIDS;

// now move asteroids around
for (row = 0; row < ASTEROIDS; row++) {
// Bounce off walls? Marginally more expensive than wrapping.
tmp1 = x[row] + dx[base + row]; // overflow test
if ((dx[base + row] > 0 && x[row] > 0 && (int8_t)(tmp1+MARGIN) < 0)
|| (dx[base + row] < 0 && x[row] < 0 && (int8_t)(tmp1-MARGIN) > 0)) {
dx[base + row] = -dx[base + row]; // bounce?
}
x[row] = x[row] + dx[base + row];

tmp1 = y[row] + dy[base + row];
if ((dy[base + row] > 0 && y[row] > 0 && (int8_t)(tmp1+MARGIN) < 0)
|| (dy[base + row] < 0 && y[row] < 0 && (int8_t)(tmp1-MARGIN) > 0)) {
dy[base + row] = -dy[base + row];
}
y[row] = y[row] + dy[base + row];

}
Wait_Recal (); Flash++;
Display_board(0);
Intensity_a (WHITE_INTENSITY);
for (row = 0; row < ASTEROIDS; row++) {
Reset0Ref ();
set_scale (MEDIUM_SCALE);
Moveto_d (y[row]-11, x[row]-1);
set_scale (TINY_SCALE);
if (row == 12) Intensity_a (BLACK_INTENSITY);
#ifdef PIZERO
Draw_Line_d(120,120);
Draw_Line_d(120,0);
Draw_Line_d(120,-120);
Draw_Line_d(0,-120);
Draw_Line_d(-120,-120);
Draw_Line_d(-120,0);
Draw_Line_d(-120,120);
Draw_Line_d(0,120);
#else
Draw_VLp((int8_t *)white_big);
#endif
}

} while (direction);

(void)tmp1;(void)base;(void)done;(void)direction; // freeze result
direction = 24;
while (--direction != 0) {
Wait_Recal (); Flash++;
Display_board(0);
Intensity_a (WHITE_INTENSITY); // use the constant (name?)
for (row = 0; row < ASTEROIDS; row++) {
Reset0Ref ();
set_scale (MEDIUM_SCALE);
Moveto_d (y[row]-11, x[row]-1);
set_scale (TINY_SCALE);
if (row == 12) Intensity_a (BLACK_INTENSITY);
#ifdef ORIGINAL
Draw_VLp ((int8_t *)white_big);
#else
Draw_Line_d(120,120);
Draw_Line_d(120,0);
Draw_Line_d(120,-120);
Draw_Line_d(0,-120);
Draw_Line_d(-120,-120);
Draw_Line_d(-120,0);
Draw_Line_d(-120,120);
Draw_Line_d(0,120);
#endif
}
}
#undef XX
#undef YY
}

```