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trying to fix Shot position calculation, better, but still wrong

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This commit is contained in:
Josh Holtrop 2012-10-06 22:47:29 -04:00
parent 69f403cee1
commit 1741476456
1 changed files with 16 additions and 12 deletions
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28
src/common/Shot.cc
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@ -7,7 +7,7 @@ using namespace sf;
/* INITIAL_SHOT_HEIGHT needs to be set to the height that the shot
* starts at, which will depend on the tank model in use */
#define INITIAL_SHOT_HEIGHT 30
#define INITIAL_SHOT_HEIGHT 10
#define GRAVITY 9.8
@ -15,22 +15,26 @@ using namespace sf;
* Assuming a constant 45° shot angle simplifies the equations.
* x = Vt
* y = H + Vt - gt²/2
* = (-g/2)t² + Vt + H
* where
* V = shot speed
* t = time
* g = gravity
* H = INITIAL_SHOT_HEIGHT
*
* We want to figure out a speed that gets us to y = 0 at our desired time.
* According to the quadratic formula (x = (-b ± sqrt(b²-4ac))/2a), y = 0 when
* t = (-V + sqrt(V² - 4*g*H/2)) / (2*g/2)
* We need to solve for V.
* tg = sqrt(V² - 2gH) - V
* tg + V = sqrt(V² - 2gH)
* (tg + V)² = V² - 2gH
* t²g² + 2tgV + V² = V² - 2gH
* t²g² + 2tgV + 2gH = 0
* (t²g² + 2gH) = -2tgV
* -(t²g² + 2gH) / (2tg) = V
* t = (-V ± sqrt(V² - 4(-g/2)H)) / 2(-g/2)
* -tg = -V ± sqrt(V² + 2gH)
* V - tg = ± sqrt(V² + 2gH)
*
* V - tg = sqrt(V² + 2gH)
* (V - tg)² = V² + 2gH
* V² - 2Vtg + t²g² = V² + 2gH
* t²g² - 2Vtg = 2gH
* -2Vtg = 2gH - t²g²
* V = -(2gH - t²g²)/2tg
* V = (t²g² - 2gH)/2tg
*
* So given the time to target (target_dist / PROJECTILE_VELOCITY) we can
* solve for what the shot's speed should be.
@ -40,7 +44,7 @@ Shot::Shot(const Vector2f & origin, double direction, double target_dist)
m_direction = Vector2f(cos(direction), sin(direction));
m_origin = origin;
double t = target_dist / PROJECTILE_VELOCITY;
m_speed = -(t * t * GRAVITY * GRAVITY + 2 * GRAVITY * INITIAL_SHOT_HEIGHT)
m_speed = (t * t * GRAVITY * GRAVITY - 2 * GRAVITY * INITIAL_SHOT_HEIGHT)
/ (2 * t * GRAVITY);
}
@ -49,6 +53,6 @@ Vector3f Shot::get_position()
float time = m_clock.getElapsedTime().asSeconds();
float horiz_dist = m_speed * time;
float z = INITIAL_SHOT_HEIGHT + m_speed * time - GRAVITY * time * time / 2.0;
Vector2f xy = m_direction * horiz_dist;
Vector2f xy = m_origin + m_direction * horiz_dist;
return Vector3f(xy.x, xy.y, z);
}