engine.core.state source code

1 /*
2     Copyright © 2020, Luna Nielsen
3     Distributed under the 2-Clause BSD License, see LICENSE file.
4     
5     Authors: Luna Nielsen
6 */
7 module engine.core.state;
8 
9 /**
10     Manager of game states
11 */
12 class GameStateManager {
13 private static:
14     GameState[] states;
15 
16 public static:
17 
18     /**
19         Update the current game state
20     */
21     void update() {
22         if (states.length == 0) return;
23         states[$-1].update();
24     }
25 
26     /**
27         Draw the current game state
28 
29         Offset sets the offset from the top of the stack to draw
30     */
31     void draw(size_t offset = 1) {
32         if (states.length == 0) return;
33 
34         // Handle drawing passthrough, this allows us to draw game boards with game over screen overlayed.
35         if (states[$-offset].drawPassthrough && states.length > offset) {
36             states[$-offset].draw();
37         }
38 
39         // Draw the current state
40         states[$-offset].draw();
41     }
42 
43     /**
44         Push a game state on to the stack
45     */
46     void push(GameState state) {
47         states ~= state;
48         states[$-1].onActivate();
49     }
50 
51     /**
52         Pop a game state from the stack
53     */
54     void pop() {
55         if (canPop) {    
56             states[$-1].onDeactivate();
57             states.length--;
58         }
59     }
60 
61     /**
62         Gets whether an element can be popped from the game state stack
63     */
64     bool canPop() {
65         return states.length > 0;
66     }
67 
68     /**
69         Pop a game state from the stack
70     */
71     void popAll() {
72         while (canPop) pop();
73     }
74 
75 }
76 
77 /**
78     A game state
79 */
80 abstract class GameState {
81 public:
82     /**
83         Wether drawing should pass-through to the previous game state (if any)
84         This allows overlaying a gamr state over an other
85     */
86     bool drawPassthrough;
87 
88     /**
89         Update the game state
90     */
91     abstract void update();
92 
93     /**
94         Draw the game state
95     */
96     abstract void draw();
97 
98     /**
99         When a state is pushed
100     */
101     void onActivate() { }
102 
103     /**
104         Called when a state is popped
105     */
106     void onDeactivate() { }
107 }