Added aim lead to platform and station weapons.

2 files changed, 46 insertions, 23 deletions

diff --git a/src/game/base/platform.cc b/src/game/base/platform.cc
index b5e92dc..4f18330 100644
--- a/src/game/base/platform.cc
+++ b/src/game/base/platform.cc
@@ -110,53 +110,74 @@ void Platform::frame(const unsigned long elapsed)
 					continue;
 				}
 		
-				// find a target for this slot
-				Ship *current_enemy = 0;
-				float current_distance = 0.0f;
-
-				math::Vector3f projectile_location(location() + (axis() * slot->location()));
+				// target location in world coordinates
+				Ship *current_enemy = 0;		// The enemy ship the slot will be targetting
+				float current_distance = 0.0f;		// Distance to the target location
+				math::Vector3f current_aim;		// Location to aim at
+				
+				// slot and projectile location in world coordinates
+				const math::Vector3f projectile_location(location() + (axis() * slot->location()));
 				math::Vector3f projectile_direction;
 				math::Axis projectile_axis(axis() * slot->axis());
-				
-				math::Vector3f aim_location;
 
 				// we only need half the cone angle for the cosine calculation
 				const float conecos = cosf(slot->cone() * 0.5f); 
 				
-				for (std::list<Ship *>::const_iterator enemy_it = enemylist.begin(); enemy_it != enemylist.end(); enemy_it++) {
+				for (std::list<Ship *>::const_iterator enemy_it = enemylist.begin(); enemy_it != enemylist.end(); enemy_it++)
+				{
+					// apply aim correction
+					// see https://www.reddit.com/r/gamedev/comments/16ceki/turret_aiming_formula/c7vbu2j
+					
+					const math::Vector3f v((*enemy_it)->axis().forward() * (*enemy_it)->speed());
+					const math::Vector3f w((*enemy_it)->location() - projectile_location);
+					
+					const float a = v.lengthsquared() - weapon->projectile_speed() * weapon->projectile_speed();
+					const float b = 2.0f * math::dotproduct(v, w);
+					const float c = w.lengthsquared();
 					
-					const float d = math::distance((*enemy_it)->location(), projectile_location);
+					const float D = b * b - 4.0f * a * c;
+					if (D < 0.0f)
+					{
+						continue;
+					} 					
+					const float t = math::min(sqrtf(D) - b , -sqrtf(D) - b) / (2.0f * a);				
+					const math::Vector3f hitpoint((*enemy_it)->location() + v * t);
 					
-					if (d > weapon->projectile_range() + (*enemy_it)->radius()) {
+					// verify the hitpoint is within weapon's range
+					const float d = math::distance(hitpoint, projectile_location);
+					if (d > weapon->projectile_range() + (*enemy_it)->radius())
+					{
 						continue;
 					}
-					if ((current_distance > 0) && (d > current_distance)) {
+					if ((current_distance > 0.0f) && (d > current_distance))
+					{
 						continue;
 					}
-					
-					aim_location.assign((*enemy_it)->location() + (*enemy_it)->axis().forward() * ( (*enemy_it)->radius() * 0.25f));
-					projectile_direction.assign(aim_location - projectile_location);
+										
+					projectile_direction.assign(hitpoint - projectile_location);
 					projectile_direction.normalize();
 					
+					// verify the hitpoint is in the slot's cone-of-fire
 					const float cosa = math::dotproduct(projectile_direction, projectile_axis.forward());
-					
-					// check if the ship is in the slot's cone if fire
-					if (cosa >= conecos) {
+					if (cosa >= conecos)
+					{
 						current_distance = d;
 						current_enemy = (*enemy_it);
+						current_aim.assign(hitpoint);
 					}
 				}
 				
-				if (current_enemy) {
-					aim_location.assign(current_enemy->location() + current_enemy->axis().forward() * (current_enemy->radius() * 0.25f));
-					projectile_direction.assign(aim_location - projectile_location);
+				if (current_enemy)
+				{
+					projectile_direction.assign(current_aim - projectile_location);
 					projectile_direction.normalize();
 					
 					const float cosa = math::dotproduct(projectile_direction, projectile_axis.forward());
 					
 					// point the projectile into the fire direction
 					math::Vector3f normal(math::crossproduct(projectile_direction, projectile_axis.forward()));
-					if (normal.length() > MIN_DELTA) {
+					if (normal.length() > MIN_DELTA)
+					{
 						float sina = sqrt(1.0f - cosa * cosa);
 						
 						normal.normalize();
@@ -184,4 +205,5 @@ void Platform::frame(const unsigned long elapsed)
 	}
 }
 
-}
+} // namespace game
+
diff --git a/src/game/base/weapon.cc b/src/game/base/weapon.cc
index 28a7ae3..c4c8ef2 100644
--- a/src/game/base/weapon.cc
+++ b/src/game/base/weapon.cc
@@ -169,7 +169,7 @@ bool Weapon::init()
 				
 				if (weapon) {
 					if (inifile.got_key_float("speed", f)) {
-						// convert speed from  meters/second to game units/second
+						// convert speed from meters/second to game units/second
 						weapon->set_projectile_speed(f * 0.01f);
 						continue;
 					
@@ -184,6 +184,7 @@ bool Weapon::init()
 						
 					} else if (inifile.got_key_float("range", f)) {
 						// range in meters, one game unit is 100 meters
+						// lifespan is in milliseconds, projectile speed in game units/second
 						if (weapon->projectile_speed() == 0) {
 							inifile.unknown_error("cannot set range if projectile speed is 0!");
 						} else {