Just in case anyone was missing me 
, I wanted to say hi again Allegro!
My absence hasn't meant I've not been programming. In fact I've been working really hard on my game and it's going very well indeed.
Here's an example of some code I wrote recently :
1/* circle_and_rotating_line_collision() : checks if a circle moving in a straight line, collides with a
2straight line which is rotating around a fixed point
3
4arguments:
5
6pai : polygon angle increment : angle in radians for how much the polygon rotated per update
7
8*/
9int circle_and_rotating_line_collision(Circle *c, const double cr_x, const double cr_y, const double pai, Point v1, Point v2, PotentialMove& move)
10{
11
12 Point v1_s, v2_s; // v1 shifted and v2 shifted by radius of circle in direction perpendicular to side of polygon away from centre of rotation
13
14
15
16 double psa2 = atan2( (v2.y - v1.y) , (v2.x - v1.x) );
17 if( psa2 < 0.0 )
18 {
19 psa2 += TWO_PI;
20 }
21
22 psa2 -= ALLEGRO_PI / 2.0f;
23
24 principal_value( &psa2 );
25
26 v1_s.x = v1.x + c->radius * cos(psa2);
27 v1_s.y = v1.y + c->radius * sin(psa2);
28 v2_s.x = v2.x + c->radius * cos(psa2);
29 v2_s.y = v2.y + c->radius * sin(psa2);
30
31 const double k = c->remaining_distance / pai; // for storing the constant value : (distance circle travels) / (polygon increment angle)
32 const double xL = v1_s.x < v2_s.x ? v1_s.x - cr_x : v2_s.x - cr_x;
33 const double yL = v1_s.x < v2_s.x ? v1_s.y - cr_y : v2_s.y - cr_y;
34 const double xR = v1_s.x < v2_s.x ? v2_s.x - cr_x : v1_s.x - cr_x;
35 const double yR = v1_s.x < v2_s.x ? v2_s.y - cr_y : v1_s.y - cr_y;
36 const double sL = sqrt( (xR - xL) * (xR - xL) + (yR - yL) * (yR - yL) ); // length of polygon side
37 const double xt = ((xL * (xR - xL)) + (yL * (yR - yL))) / sL; // xt : x translation for the spiral
38 const double yt = (yL * xR - xL * yR) / sL; // yt : y translation for the spiral
39 const double cos_psa = (xR - xL) / sL; // cosine of the angle side of polygon makes
40 const double sin_psa = (yR - yL) / sL; // sine of the angle side of polygon makes
41 double pc[7]; // polynomial coeffecients
42 double z[ 12 ]; // array for real and imaginary parts of solutions to polynomial
43 int i;
44 gsl_poly_complex_workspace *w = gsl_poly_complex_workspace_alloc (7);
45
46 double r, pA;
47
48 double a = c->cc_x - cr_x;
49 double b = c->cc_y - cr_y;
50
51 //cout << "a" << a << "b" << b << "\n";
52 double psa = atan2( yR - yL, xR - xL );
53
54 if( psa < 0.0f )
55 {
56 psa += TWO_PI;
57 }
58
59
60 //cout << "psa = " << psa << "\n";
61
62 pc[0] = b * cos_psa - a * sin_psa - yt;
63 pc[1] = k * sin(c->circle_angle) * cos_psa - a * cos_psa - k * cos(c->circle_angle) * sin_psa - b * sin_psa;
64 pc[2] = - b * cos_psa / 2.0f + a * sin_psa / 2.0f - k * sin(c->circle_angle) * sin_psa - k * cos(c->circle_angle) * cos_psa;
65 pc[3] = k * sin(c->circle_angle) * cos_psa / 2.0f + a * cos_psa / 6.0 + b * sin_psa / 6.0f + k * cos(c->circle_angle) * sin_psa / 2.0f;
66 pc[4] = b * cos_psa / 24.0f - a * sin_psa / 24.0f + k * cos(c->circle_angle) * cos_psa / 6.0f + k * sin(c->circle_angle) * sin_psa / 6.0f;
67 pc[5] = k * sin(c->circle_angle) * cos_psa / 24.0f - k * cos(c->circle_angle) * sin_psa / 24.0f - a * cos_psa / 120.0f - b * sin_psa / 120.0f;
68 pc[6] = - k * cos(c->circle_angle) * cos_psa / 120.0f - k * sin(c->circle_angle) * sin_psa / 120.0f;
69
70 gsl_poly_complex_solve(pc, 7, w, z);
71
72 for(i = 0; i < 6; ++i)
73 {
74 if( z[ 2 * i + 1] == 0.0)
75 {
76 r = sqrt( pow( b + k * z[2*i] * sin( c->circle_angle ), 2) + pow( a + k * z[2*i] * cos( c->circle_angle ), 2) );
77
78 pA = atan2( b + k * z[2*i] * sin( c->circle_angle ), a + k * z[2*i] * cos( c->circle_angle ));
79
80 if( z[2*i] >= 0.0 && z[2*i] <= pai && r * cos( pA - z[2*i] - psa) - xt >= 0 && r * cos( pA - z[2*i] - psa ) - xt <= sL )
81 {
82
83 double hit_x, hit_xr;
84 double hit_y, hit_yr;
85
86 //cout << "degrees required to hit " << (z[2*i] * 180.0f / ALLEGRO_PI) << "\n";
87
88 rotate_point( psa, r * cos( pA - z[2*i] - psa), r * sin( pA - z[2*i] - psa), &hit_x, &hit_y);
89 rotate_point( z[2*i], hit_x, hit_y, &hit_xr, &hit_yr);
90
91 move.x = hit_xr + cr_x;
92 move.y = hit_yr + cr_y;
93
94 double xLr, yLr, xRr, yRr; // for storing where the coordinates of the ends of the line where it
95 // it is when the circle hits it
96
97 // rotate points (xL, yL) and (xR, yR) to where they are when circle hits it so the angle of it
98 // can be worked out. This is needed to determine the angle the circle bounces off at
99
100 rotate_point(z[2*i], xL, yL, &xLr, &yLr);
101 rotate_point(z[2*i], xR, yR, &xRr, &yRr);
102
103 double side_angle = atan2( yRr - yLr, xRr - xLr );
104
105 double new_angle = 2.0f * side_angle - c->circle_angle;
106
107 principal_value(&new_angle);
108
109 move.angle = new_angle;
110
111 //cout << "returning 1 from rotating line function.\n";
112 //eek();
113
114 return 1;
115 }
116 }
117
118 }
119
120 //cout << "rotating line function : returning 0.\n";
121
122 return 0;
123}
It took me weeks to work it out but it works good. Very proud to have worked it out.
So here I am, finally getting somewhere with my game and they want to rope me in for a medical assessment to see if I'm fit for work.
Also, I'm now doing a maths degree and playing ping ping once a week.
Anyway, hope everyone's getting on alright,
Will
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