void DrawArrow(GG::Pt begin, GG::Pt end) {
double head_width = 5.0;
// A vector (math) of the arrow we wish to draw
GG::Pt direction = end - begin;
double length = sqrt(1.0*(Value(direction.x)*Value(direction.x) +
Value(direction.y)*Value(direction.y)));
if (length == 0) {
return;
}
// The point in the main line of the arrow,
// paraller to which the head ends
// \.
// \.
// --------h-->
// /.
// /.
// h is at the handle
GG::Pt handle;
// How much to move off the handle to get to
// the end point of one of the head lines
GG::X delta_x;
GG::Y delta_y;
if (direction.x != 0 && direction.y != 0) {
// In a skewed arrow we need
// a bit of geometry to figure out the head
double x = Value(direction.x);
double y = Value(direction.y);
double normalizer = head_width / sqrt(1 + x*x / (y*y));
delta_x = GG::X(normalizer);
delta_y = GG::Y(- x / y * normalizer);
handle = end - GG::Pt((head_width / length) * direction.x, (head_width / length) * direction.y);
} else if (direction.x == 0) {
// Vertical arrow
handle = end;
handle.y -= boost::math::sign(Value(direction.y))*GG::Y(head_width);
delta_x = GG::X(head_width);
delta_y = GG::Y0;
} else {
//horizontal arrow
handle = end;
handle.x -= boost::math::sign(Value(direction.x)) * GG::X(head_width);
delta_x = GG::X0;
delta_y = GG::Y(head_width);
}
GG::Pt left_head = handle;
GG::Pt right_head = handle;
left_head.x += delta_x;
left_head.y += delta_y;
// The other line is on the opposite side of the handle
right_head.x -= delta_x;
right_head.y -= delta_y;
GG::glColor(GG::CLR_WHITE);
glLineWidth(2);
glDisable(GL_TEXTURE_2D);
GG::GL2DVertexBuffer verts;
verts.reserve(6);
verts.store(Value(begin.x), Value(begin.y));
verts.store(Value(end.x), Value(end.y));
verts.store(Value(end.x), Value(end.y));
verts.store(Value(left_head.x), Value(left_head.y));
verts.store(Value(end.x), Value(end.y));
verts.store(Value(right_head.x),Value(right_head.y));
verts.activate();
glDrawArrays(GL_LINES, 0, verts.size());
glEnable(GL_TEXTURE_2D);
}
