Modifying the Keyboard State Array

In SDL, the keyboard state array obtained through SDL_GetKeyboardState() is marked as const.

This means you cannot modify it directly. The array is managed internally by SDL, and changing it directly would lead to unpredictable behavior and potentially crash your application.

Why You Shouldn’t Modify the Array

1. Data Integrity: SDL uses the keyboard state array to keep track of the current state of the keyboard. Modifying it directly would corrupt this state, leading to incorrect input handling.
2. Consistency: SDL expects the array to remain unchanged. Direct modifications would break the consistency of the input handling mechanism within SDL.
3. Stability: SDL is responsible for updating the array based on real-time input events. If you modify it, SDL's internal logic might not function correctly, leading to crashes or undefined behavior.

Alternative Approach

If you need to simulate key presses or modify input behavior, you should handle this at a higher level in your application logic rather than altering the internal SDL state.

For instance, you can create your own input handling system to simulate key presses.

Example

Here’s an example of how you can create a custom input handler to simulate key presses:

1#include <SDL.h>
2#include <iostream>
3#include <unordered_map>
4#include <unordered_set>
5
6class InputHandler {
7 public:
8  void Update() {
9    // Reset simulated keys
10    simulatedKeys.clear();
11
12    // Get actual keyboard state
13    const Uint8* state = SDL_GetKeyboardState(NULL);
14
15    // Process actual key states
16    for (const auto& key : keysToMonitor) {
17      keyStates[key] = state[key];
18    }
19
20    // Example: Simulate space key being pressed
21    if (state[SDL_SCANCODE_LEFT]
22      && state[SDL_SCANCODE_RIGHT]) {
23      simulatedKeys[SDL_SCANCODE_SPACE] = true;
24    }
25  }
26
27  bool IsKeyPressed(SDL_Scancode key) const {
28    auto it = simulatedKeys.find(key);
29    if (it != simulatedKeys.end()) {
30      return it->second;
31    }
32    return keyStates.at(key);
33  }
34
35  void MonitorKey(SDL_Scancode key) {
36    keysToMonitor.insert(key); }
37
38 private:
39  std::unordered_map<SDL_Scancode, bool> keyStates;
40  std::unordered_map<SDL_Scancode, bool> simulatedKeys;
41  std::unordered_set<SDL_Scancode> keysToMonitor;
42};
43
44int main(int argc, char* argv[]) {
45  SDL_Init(SDL_INIT_VIDEO);
46
47  SDL_Window* window = SDL_CreateWindow(
48    "Custom Input Handling",
49    SDL_WINDOWPOS_CENTERED,
50    SDL_WINDOWPOS_CENTERED,
51    640, 480, SDL_WINDOW_SHOWN
52  );
53
54  InputHandler inputHandler;
55  inputHandler.MonitorKey(SDL_SCANCODE_LEFT);
56  inputHandler.MonitorKey(SDL_SCANCODE_RIGHT);
57  inputHandler.MonitorKey(SDL_SCANCODE_SPACE);
58
59  bool running = true;
60  SDL_Event event;
61
62  while (running) {
63    while (SDL_PollEvent(&event)) {
64      if (event.type == SDL_QUIT) {
65        running = false;
66      }
67    }
68
69    inputHandler.Update();
70
71    if (inputHandler.IsKeyPressed(SDL_SCANCODE_SPACE)) {
72      std::cout << "Simulated Space key pressed\n";
73    }
74
75    // Rendering code here
76  }
77
78  SDL_DestroyWindow(window);
79  SDL_Quit();
80  return 0;
81}

1Simulated Space key pressed

Explanation

• Custom Input Handler: The InputHandler class monitors specific keys and allows for simulating key presses.
• Update Method: The Update() method checks the current state of monitored keys and sets simulated key states based on custom logic.
• IsKeyPressed Method: This method checks if a key is pressed, considering both actual and simulated key states.
• Simulating Keys: In this example, the space key is simulated to be pressed when both the left and right arrow keys are pressed simultaneously.

Conclusion

In summary, you should not modify the keyboard state array obtained from SDL_GetKeyboardState().

Doing so would lead to unstable and inconsistent behavior in your application. Instead, handle your input logic at a higher level, using the state array as a read-only reference to the current keyboard state.