I'm trying to make a card game where the cards fan out. Right now to display it Im using the Allegro API which has a function:
al_draw_rotated_bitmap(OBJECT_TO_ROTATE,CENTER_X,CENTER_Y,X
,Y,DEGREES_TO_ROTATE_IN_RADIANS);
so with this I can make my fan effect easily. The problem is then knowing which card is under the mouse. To do this I thought of doing a polygon collision test. I'm just not sure how to rotate the 4 points on the card to make up the polygon. I basically need to do the same operation as Allegro.
for example, the 4 points of the card are:
card.x
card.y
card.x + card.width
card.y + card.height
I would need a function like:
POINT rotate_point(float cx,float cy,float angle,POINT p)
{
}
Thanks
ベストアンサー1
First subtract the pivot point (cx,cy)
, then rotate it (counter clock-wise), then add the point again.
POINT rotate_point(float cx, float cy, float angleInRads, POINT p)
{
float s = sin(angleInRads);
float c = cos(angleInRads);
// translate point back to origin:
p.x -= cx;
p.y -= cy;
// rotate point
float xnew = p.x * c - p.y * s;
float ynew = p.x * s + p.y * c;
// translate point back:
p.x = xnew + cx;
p.y = ynew + cy;
return p;
}