First of all, I thank you two for the excellent replies. I haven't completely understand it yet, but now I have stronger clues.
Yes, I have the angle when the left mouse button is pressed; as you've said, I draw the rotated bitmap already. I do so here:
#SelectExpand
1al_draw_rotated_bitmap(playerTux, defaultPlayer1.size
/ 2, defaultPlayer1.size
/ 2,
2defaultPlayer1.pos
[0], defaultPlayer1.pos
[1], mousePos
/ mouseSensitivity,
0);
For you to understand it more clearly, the angle in this case is a division of mousePos with a constant called mouseSensitivity (Giving the fact that it is a shooter game, I found a way to give to the user the option of choosing between 4 sensitivities.)
The rotation of the bitmap involves a curious solution that I've found:
#SelectExpand
1if (ev.type
== ALLEGRO_EVENT_MOUSE_AXES
) {
2
3// This says that the variable mousePos equals to the movement of the mouse
4// in the x axis, which is something necessary to change the angle of the image.
5
6 mousePos
= ev.mouse.x
;
7
8
9// I had several problems with the image stoping to rotate when the mouse
10// goes off the screen area. So this basically warps the mouse cursor to the
11// beginning of the screen when it goes off it, and vice-versa. To examine
12// how this works, put a comment in the "al_hide_mouse_cursor()" up there.
13
14 if (mousePos
>= screenWidth
- 1) { // If the mouse cursor goes off the screen (right),
15 al_set_mouse_xy(display,
1,
0); } // warp it to the beginning of the screen.
16 if (mousePos
< 1) { // If the mouse cursor goes off the screen (left),
17 al_set_mouse_xy(display, screenWidth
- 1,
0); } } // warp it to the end of the screen.
This "mouse cursor teleportation" solved perfectly an old problem of mine (Maybe there's a clever way to solve this, but if it is, I don't know it yet).
The "mouseSensitivity" is declared together with the mousePos in this way:
#SelectExpand
1float mousePos = 0.0;
2float mouseSensitivity = LOW_MOUSE_SENSITIVITY;
LOW_MOUSE_SENSITIVITY is a constant, defined together with these ones:
#SelectExpand
1#define PLAYER_ROTATION_FACTOR 81.2
2#define VERY_LOW_MOUSE_SENSITIVITY PLAYER_ROTATION_FACTOR * 2
3#define LOW_MOUSE_SENSITIVITY PLAYER_ROTATION_FACTOR
4#define MEDIUM_MOUSE_SENSITIVITY PLAYER_ROTATION_FACTOR / 2
5#define HIGH_MOUSE_SENSITIVITY PLAYER_ROTATION_FACTOR / 2 / 2
This "rotation factor" is a solution to a terrible problem. When I've put the mouse.x as an angle argument to draw the rotated bitmap; even with the pivot placed properly, the bitmap didn't rotate completely (360), and then, by testing endlessly, I found that when I divided the mousePos with this value (81.2), the turn was complete (And therefore, mathematically speaking, I could double it's value to get a slower turn, but a still complete turn). I don't know if this all is clear enough, but it's working perfectly.
The thing is, thanks to this odd division, the angle does not go from 0 to 360; instead, it goes from 0.000000 to 6.299999. If I print this angle multiplied by something closer to 28 I can get the 360, but it's irrelevant. Now I've come to my actual problem, and I'm trying to apply this atan2() like this:
#SelectExpand
1 double playerPosArray1X
[2] = {defaultPlayer1.pos
[0], defaultPlayer2.pos
[0]};
2 double playerPosArray1Y
[2] = {defaultPlayer1.pos
[1], defaultPlayer2.pos
[1]};
3 double angleCalculation
= atan2(playerPosArray1Y, playerPosArray1X
);
And then, inside the loop:
#SelectExpand
1printf("Angle Calculation: %f\n", angleCalculation
);
But I receive the following error in terminal:
main.c: In function ‘main’:
main.c:84:2: error: incompatible type for argument 1 of ‘atan2’
In file included from /usr/include/math.h:71:0,
from main.c:22:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:61:1: note: expected ‘double’ but argument is of type ‘double *’
main.c:84:2: error: incompatible type for argument 2 of ‘atan2’
In file included from /usr/include/math.h:71:0,
from main.c:22:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:61:1: note: expected ‘double’ but argument is of type ‘double *’
make: *** [main] Error 1
So, I can't pass an array as an argument of atan2(), and I'm still quite lost. But I'll keep studying... After all, that's what game development is all about, right? Solving terrible problems in the most efficient way 
.
Thank you very much again!
]]>
) to the atan2 function this way....while he SHOULD get the angle between the first two values, this is not formally correct, is it?
. We can also represent this angle's direction as a unit vector (that is a vector that strictly has a magnitude of 1). The unit vector (we'll call this 
) is composed of an x component and a y component, which can be derived from the angle we have:
) ...you mean determine on which "half" of segment and arbitrary point is located? ...or you mean determine in which region of space the point lies in regards of the line?