72 lines
2.0 KiB
C++
72 lines
2.0 KiB
C++
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#include <math.h>
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#include "Shot.h"
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#include "Types.h"
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using namespace sf;
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/* INITIAL_SHOT_HEIGHT needs to be set to the height that the shot
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* starts at, which will depend on the tank model in use */
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#define INITIAL_SHOT_HEIGHT 10
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/* GRAVITY can really be any arbitrary value that makes the shot's speed
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* feel right. Increasing the gravity will decrease the amount of time
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* it takes the shot to hit its target. */
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#define GRAVITY 150
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#define SHOT_ANGLE 30
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/* We model the shot's position using a parametric equation based on time.
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* x = vct
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* y = h + vst - gt²/2
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* = (-g/2)t² + vst + h
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* where
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* s = sin(shot angle)
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* c = cos(shot angle)
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* v = shot speed
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* t = time
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* g = gravity
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* h = INITIAL_SHOT_HEIGHT
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*
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* Given a target distance of d, we want to figure out a speed that makes
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* (x, y) = (d, 0) a valid point on the trajectory.
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* Then:
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* d = vct
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* 0 = (-g/2)t² + vst + h
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* So:
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* v = d/ct
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* 0 = (-g/2)t² + (d/ct)st + h
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* 0 = (-g/2)t² + ds/c + h
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* According to the quadratic formula (x = (-b ± sqrt(b² - 4ac))/2a),
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* t = ±sqrt(-4(-g/2)(ds/c+h)) / 2(-g/2)
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* -tg = ±sqrt(2g(ds/c+h))
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* t²g² = 2g(ds/c+h)
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* t² = 2(ds/c+h)/g
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* t = sqrt(2(ds/c+h)/g)
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* Now that we know the time at which this point occurs, we can solve for
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* the shot speed (v)
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* v = d/ct
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* v = d / c / sqrt(2(ds/c+h)/g)
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*/
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Shot::Shot(const Vector2f & origin, double direction, double target_dist)
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{
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m_direction = Vector2f(cos(direction), sin(direction));
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m_origin = origin;
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m_cos_a = cos(SHOT_ANGLE * M_PI / 180.0);
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m_sin_a = sin(SHOT_ANGLE * M_PI / 180.0);
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m_speed = target_dist / m_cos_a /
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sqrt(2 * (target_dist * m_sin_a / m_cos_a + INITIAL_SHOT_HEIGHT) /
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GRAVITY);
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m_duration = target_dist / (m_speed * m_cos_a);
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}
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Vector3f Shot::get_position()
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{
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float time = get_elapsed_time();
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float horiz_dist = m_speed * m_cos_a * time;
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float z = INITIAL_SHOT_HEIGHT + m_speed * m_sin_a * time -
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GRAVITY * time * time / 2.0;
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Vector2f xy = m_origin + m_direction * horiz_dist;
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return Vector3f(xy.x, xy.y, z);
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}
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