init, working screens from raylib screens example and basic bullets mechanics

game.odin

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+package space_invaders
+
+import "core:c"
+import "core:log"
+import glm "core:math/linalg/glsl"
+
+import rl "vendor:raylib"
+
+GLOBAL_SPRITE_SCALE :: 2
+
+ALIEN_ROWS :: 5
+ALIENS_PER_ROW :: 11
+ALIENS :: ALIEN_ROWS * ALIENS_PER_ROW
+ALIEN_SIDE_STEP :: 20 * GLOBAL_SPRITE_SCALE
+ALIEN_RECT :: glm.ivec2{16 * GLOBAL_SPRITE_SCALE, 16 * GLOBAL_SPRITE_SCALE}
+
+MAX_BULLETS :: 100
+BULLET_SPEED :: 240
+BULLET_RECT :: glm.ivec2{16 * GLOBAL_SPRITE_SCALE, 16 * GLOBAL_SPRITE_SCALE}
+
+MAX_PLAYER_HEALTH :: 3
+PLAYER_SPEED :: 40
+PLAYER_RECT :: glm.ivec2{16 * GLOBAL_SPRITE_SCALE, 16 * GLOBAL_SPRITE_SCALE}
+
+Alien :: struct {
+	alive:    bool,
+	position: glm.vec2,
+	id:       int,
+}
+
+Bullet :: struct {
+	alive:    bool,
+	position: glm.vec2,
+}
+
+setup_game :: proc(state: ^GameState) {
+	using state
+	player_pos = glm.vec2{f32(screen_width / 2), f32(screen_height - PLAYER_RECT.x)}
+
+	// setup the initial positions of the aliens
+	for row in 0 ..< ALIEN_ROWS {
+		for alien in 0 ..< ALIENS_PER_ROW {
+			aliens[(row * ALIENS_PER_ROW) + alien].position = glm.vec2 {
+				f32((alien + 1) * int(ALIEN_RECT.x + 10)),
+				f32((row + 1) * int(ALIEN_RECT.x + 10)),
+			}
+		}
+	}
+}
+
+update_game :: proc(state: ^GameState) {
+	using state
+
+	// If we're entering the game screen then we need to setup initial state of the game variables
+	if last_frame_screen != .GAMEPLAY {
+		setup_game(state)
+		log.info("Done setting up game")
+	}
+
+	// Press enter to change to ENDING screen
+	if (rl.IsKeyPressed(rl.KeyboardKey.ENTER)) {
+		state.screen = .ENDING
+		log.info("Updated screen enum", state.screen)
+	}
+
+	// Press space to change to fire
+	if (rl.IsKeyPressed(rl.KeyboardKey.SPACE)) {
+		log.info("FIRE!")
+    bullet := &bullets[bullet_index]
+    bullet.alive = true
+    bullet.position = player_pos
+    bullet.position.y = bullet.position.y - f32((PLAYER_RECT.y / 2) + BULLET_RECT.y / 2)
+	}
+
+	if (rl.IsKeyDown(rl.KeyboardKey.RIGHT)) {
+		player_pos.x = player_pos.x + f32(PLAYER_SPEED * delta_time)
+	}
+	if (rl.IsKeyDown(rl.KeyboardKey.LEFT)) {
+		player_pos.x = player_pos.x - f32(PLAYER_SPEED * delta_time)
+	}
+
+  // movement update
+  {
+    for &bullet in bullets {
+      if bullet.alive {
+        bullet.position.y = bullet.position.y - f32(BULLET_SPEED * delta_time)
+      }
+    }
+  }
+}
+
+draw_game :: proc(state: ^GameState) {
+	using state
+	rl.DrawRectangle(0, 0, state.screen_width, state.screen_height, rl.BLACK)
+	// rl.DrawText("GAMEPLAY SCREEN", 20, 20, 40, rl.MAROON)
+	// rl.DrawText("PRESS ENTER or TAP to JUMP to ENDING SCREEN", 130, 220, 20, rl.MAROON)
+	rl.DrawCircle(c.int(player_pos.x), c.int(player_pos.y), f32(PLAYER_RECT.x / 2), rl.RED)
+
+	for row in 0 ..< ALIEN_ROWS {
+		for alien in 0 ..< ALIENS_PER_ROW {
+			alien := &aliens[(row * ALIENS_PER_ROW) + alien]
+			rl.DrawCircle(
+				c.int(alien.position.x),
+				c.int(alien.position.y),
+				f32(ALIEN_RECT.x / 2),
+				rl.YELLOW,
+			)
+		}
+	}
+
+  for &bullet in bullets {
+    if !bullet.alive { continue }
+    rl.DrawCircle(c.int(bullet.position.x), c.int(bullet.position.y), f32(BULLET_RECT.x / 2), rl.WHITE)
+  }
+
+	// rl.DrawText("GAMEPLAY SCREEN", 20, 20, 40, rl.MAROON)
+}