#23 Solve issue with tunneling

[Valeriy Halakhov]

If snake speed will be too fast or it will be refresh time delay, the snake can go out of screen box (border)

[Valeriy Halakhov]

It is possible use cross lines to check is snake moving head vector cross border.
Cross lines algorithm sample
http://algolist.manual.ru/maths/geom/intersect/lineline2d.php

[Valeriy Halakhov]

One more sample with lines
http://e-maxx.ru/algo/segments_intersection_checking

[Valeriy Halakhov]

Note: Cross lines is not good enough. If time delay will be quite big the collision with other dynamic bodies can be detected. It is not critical in scope of this game. Snake game do not have other dynamic body. Only snake.

[Valeriy Halakhov]

Cross line code sample:
BOOL CrossLine(long x1, long y1, long x2, long y2, long x3, long y3, long x4, long y4, long &x, long &y) {
long dx1 = x2 - x1;
long dy1 = y2 - y1;
long dx2 = x4 - x3;
long dy2 = y4 - y3;
x = dy1 * dx2 - dy2 * dx1;
if(!x || !dx2)
return
false;
y = x3 * y4 - y3 * x4;
x = ((x1 * y2 - y1 * x2) * dx2 - y * dx1) / x;
y = (dy2 * x - y) / dx2;
return
((x1 <= x && x2 >= x) || (x2 <= x && x1 >= x)) && ((x3 <= x && x4 >= x) || (x4 <= x && x3 >= x));
}