add gravitator. closes #11

src/spaced/spaced/game/gravitator.cpp

@@ -0,0 +1,39 @@
+#include <glm/gtx/norm.hpp>
+#include <spaced/game/Gravitator.hpp>
+
+namespace spaced {
+void Gravitator::tick(bave::Seconds dt) {
+	dt += m_residue;
+	if (dt > max_dt) { return; }
+	for (; dt > 0s; dt -= time_slice) { integrate(); }
+	m_residue = dt;
+}
+
+void Gravitator::integrate() {
+	auto const to_target = target - position;
+
+	if (glm::length2(to_target) < min_distance * min_distance) {
+		position = target;
+		return;
+	}
+
+	auto const gx = position.x;
+	auto const gy = position.y;
+	auto const mx = target.x;
+	auto const my = target.y;
+
+	auto force_x = mx - gx;
+	auto force_y = my - gy;
+	auto mag = sqrt((force_x * force_x) + (force_y * force_y));
+	mag = std::max(tiny_value, mag);
+	auto strength = force / mag * mag;
+	force_x *= strength;
+	force_y *= strength;
+	auto const acceleration = glm::vec2{force_x, force_y};
+
+	auto const dv = acceleration * time_slice.count();
+	m_velocity += dv;
+	m_velocity *= (1.0f - dampen);
+	position += m_velocity * time_slice.count();
+}
+} // namespace spaced

src/spaced/spaced/game/gravitator.hpp

@@ -0,0 +1,26 @@
+#pragma once
+#include <bave/core/time.hpp>
+#include <glm/vec2.hpp>
+
+namespace spaced {
+float const tiny_value{0.001f};
+class Gravitator {
+  public:
+	glm::vec2 target{};
+	glm::vec2 position{};
+
+	bave::Seconds time_slice{1.0f / 250.0f};
+	bave::Seconds max_dt{0.8s};
+	float dampen{0.9f};
+	float force{0.01f};
+	float min_distance{0.1f};
+
+	void tick(bave::Seconds dt);
+
+  private:
+	void integrate();
+
+	glm::vec2 m_velocity{};
+	bave::Seconds m_residue{};
+};
+} // namespace spaced

src/spaced/spaced/game/weapons/gun_beam.cpp

@@ -35,7 +35,7 @@ class LaserCharge : public IWeaponRound {
 		auto right_x = 0.5f * world_space.x;
 		for (auto const& entry : m_entries) {
 			if (entry.target->take_damage(m_config.dps * dt.count())) {
-				right_x = entry.target->get_bounds().top_left().x;
+				right_x = entry.target->get_bounds().centre().x;
 				break;
 			}
 		}

src/spaced/spaced/game/weapons/gun_beam.hpp

@@ -5,7 +5,7 @@ namespace spaced {
 class GunBeam final : public Weapon {
   public:
 	struct Config {
-		float beam_height{5.0f};
+		float beam_height{12.0f};
 		bave::Seconds fire_duration{2s};
 		bave::Seconds reload_delay{1s};
 		bave::Rgba beam_tint{bave::red_v};

src/spaced/spaced/game/world.cpp

@@ -62,9 +62,9 @@ void World::tick(Seconds const dt) {
 }
 
 void World::draw(Shader& shader) const {
+	player.draw(shader);
 	for (auto const& spawner : m_enemy_spawners) { spawner.draw(shader); }
 	for (auto const& powerup : m_powerups) { powerup->draw(shader); }
-	player.draw(shader);
 }
 
 void World::load(WorldSpec const& spec) {