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introduced tunable shot angle

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This commit is contained in:
Josh Holtrop 2012-10-07 08:14:47 -04:00
parent f1809bf193
commit 8a74d6dd2a
2 changed files with 30 additions and 21 deletions
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49
src/common/Shot.cc
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@ -12,14 +12,17 @@ using namespace sf;
/* GRAVITY can really be any arbitrary value that makes the shot's speed /* GRAVITY can really be any arbitrary value that makes the shot's speed
* feel right. Increasing the gravity will decrease the amount of time * feel right. Increasing the gravity will decrease the amount of time
* it takes the shot to hit its target. */ * it takes the shot to hit its target. */
#define GRAVITY 30 #define GRAVITY 100
#define SHOT_ANGLE 30
/* We model the shot's position using a parametric equation based on time. /* We model the shot's position using a parametric equation based on time.
* Assuming a constant 45° shot angle simplifies the equations. * x = vct
* x = vt * y = h + vst - gt²/2
* y = h + vt - gt²/2 * = (-g/2)t² + vst + h
* = (-g/2)t² + vt + h
* where * where
* s = sin(shot angle)
* c = cos(shot angle)
* v = shot speed * v = shot speed
* t = time * t = time
* g = gravity * g = gravity
@ -28,36 +31,40 @@ using namespace sf;
* Given a target distance of d, we want to figure out a speed that makes * Given a target distance of d, we want to figure out a speed that makes
* (x, y) = (d, 0) a valid point on the trajectory. * (x, y) = (d, 0) a valid point on the trajectory.
* Then: * Then:
* d = vt * d = vct
* 0 = (-g/2)t² + vt + h * 0 = (-g/2)t² + vst + h
* So: * So:
* v = d/t * v = d/ct
* 0 = (-g/2)t² + (d/t)t + h * 0 = (-g/2)t² + (d/ct)st + h
* 0 = (-g/2)t² + d + h * 0 = (-g/2)t² + ds/c + h
* According to the quadratic formula (x = (-b ± sqrt(b² - 4ac))/2a), * According to the quadratic formula (x = (-b ± sqrt(b² - 4ac))/2a),
* t = ±sqrt(-4(-g/2)(d+h)) / 2(-g/2) * t = ±sqrt(-4(-g/2)(ds/c+h)) / 2(-g/2)
* -tg = ±sqrt(2g(d+h)) * -tg = ±sqrt(2g(ds/c+h))
* t²g² = 2g(d+h) * t²g² = 2g(ds/c+h)
* t² = 2(d+h)/g * t² = 2(ds/c+h)/g
* t = sqrt(2(d+h)/g) * t = sqrt(2(ds/c+h)/g)
* Now that we know the time at which this point occurs, we can solve for * Now that we know the time at which this point occurs, we can solve for
* the shot speed (v) * the shot speed (v)
* v = d/t * v = d/ct
* v = d / sqrt(2(d+h)/g) * v = d / c / sqrt(2(ds/c+h)/g)
*/ */
Shot::Shot(const Vector2f & origin, double direction, double target_dist) Shot::Shot(const Vector2f & origin, double direction, double target_dist)
{ {
m_direction = Vector2f(cos(direction), sin(direction)); m_direction = Vector2f(cos(direction), sin(direction));
m_origin = origin; m_origin = origin;
m_speed = target_dist / m_cos_a = cos(SHOT_ANGLE * M_PI / 180.0);
sqrt(2 * (target_dist + INITIAL_SHOT_HEIGHT) / GRAVITY); m_sin_a = sin(SHOT_ANGLE * M_PI / 180.0);
m_speed = target_dist / m_cos_a /
sqrt(2 * (target_dist * m_sin_a / m_cos_a + INITIAL_SHOT_HEIGHT) /
GRAVITY);
} }
Vector3f Shot::get_position() Vector3f Shot::get_position()
{ {
float time = m_clock.getElapsedTime().asSeconds(); float time = m_clock.getElapsedTime().asSeconds();
float horiz_dist = m_speed * time; float horiz_dist = m_speed * m_cos_a * time;
float z = INITIAL_SHOT_HEIGHT + m_speed * time - GRAVITY * time * time / 2.0; float z = INITIAL_SHOT_HEIGHT + m_speed * m_sin_a * time -
GRAVITY * time * time / 2.0;
Vector2f xy = m_origin + m_direction * horiz_dist; Vector2f xy = m_origin + m_direction * horiz_dist;
return Vector3f(xy.x, xy.y, z); return Vector3f(xy.x, xy.y, z);
} }

2
src/common/Shot.h
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@ -13,6 +13,8 @@ class Shot
sf::Vector2f m_origin; sf::Vector2f m_origin;
sf::Vector2f m_direction; sf::Vector2f m_direction;
double m_speed; double m_speed;
double m_cos_a;
double m_sin_a;
sf::Clock m_clock; sf::Clock m_clock;
}; };