feat: 添加子弹类

app/src/main/java/net/imshit/aircraftwar/element/bullet/AbstractBullet.kt

@@ -0,0 +1,18 @@
+package net.imshit.aircraftwar.element.bullet
+
+import net.imshit.aircraftwar.element.AbstractFlyingObject
+import net.imshit.aircraftwar.logic.Games
+
+abstract class AbstractBullet(
+    game: Games, initialX: Float, initialY: Float, speedX: Float, speedY: Float, val power: Int
+) : AbstractFlyingObject(
+    game = game, initialX = initialX, initialY = initialY, speedX = speedX, speedY = speedY
+) {
+    override fun forward(timeMs: Int) {
+        super.forward(timeMs)
+        // 额外判定 y 轴出界
+        if (this.y <= 0) {
+            vanish()
+        }
+    }
+}

app/src/main/java/net/imshit/aircraftwar/element/bullet/EnemyBullet.kt

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+package net.imshit.aircraftwar.element.bullet
+
+import net.imshit.aircraftwar.logic.Games
+import net.imshit.aircraftwar.util.listener.EnemyListener
+import net.imshit.aircraftwar.util.listener.GameEvents
+
+class EnemyBullet(
+    game: Games, initialX: Float, initialY: Float, speedX: Float, speedY: Float, power: Int
+) : AbstractBullet(
+    game = game,
+    initialX = initialX,
+    initialY = initialY,
+    speedX = speedX,
+    speedY = speedY,
+    power = power
+), EnemyListener {
+    override val image = game.images.bulletEnemy
+    override fun notify(e: GameEvents) {
+        when (e) {
+            GameEvents.BOMB_ACTIVATE -> this.vanish()
+        }
+    }
+}

app/src/main/java/net/imshit/aircraftwar/element/bullet/HeroBullet.kt

@@ -0,0 +1,16 @@
+package net.imshit.aircraftwar.element.bullet
+
+import net.imshit.aircraftwar.logic.Games
+
+class HeroBullet(
+    game: Games, initialX: Float, initialY: Float, speedX: Float, speedY: Float, power: Int
+) : AbstractBullet(
+    game = game,
+    initialX = initialX,
+    initialY = initialY,
+    speedX = speedX,
+    speedY = speedY,
+    power = power
+) {
+    override val image = game.images.bulletHero
+}