Understanding Keyboard State

Handling Multiple Key Presses

How can I handle multiple key presses simultaneously using SDL_GetKeyboardState()?

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Handling multiple key presses simultaneously in SDL is straightforward using SDL_GetKeyboardState().

This function provides a snapshot of the keyboard state, which you can then query to check if specific keys are pressed.

Example

Here’s an example that demonstrates how to handle multiple key presses:

#include <SDL.h>
#include <iostream>

class Window {
public:
  Window() {
    SDL_Init(SDL_INIT_VIDEO);
    SDLWindow = SDL_CreateWindow(
      "Multiple Key Presses",
      SDL_WINDOWPOS_CENTERED,
      SDL_WINDOWPOS_CENTERED,
      640, 480, SDL_WINDOW_SHOWN
    );
  }

  ~Window() {
    SDL_DestroyWindow(SDLWindow);
    SDL_Quit();
  }

  void HandleKeyboard() {
    const Uint8* state = SDL_GetKeyboardState(NULL);
    if (state[SDL_SCANCODE_W] && state[SDL_SCANCODE_A]) {
      std::cout << "W and A keys are pressed\n";
    } else if (state[SDL_SCANCODE_W]) {
      std::cout << "W key is pressed\n";
    } else if (state[SDL_SCANCODE_A]) {
      std::cout << "A key is pressed\n";
    } else {
      std::cout << "Neither W nor A keys pressed\n";
    }
  }

private:
  SDL_Window* SDLWindow{nullptr};
};

int main(int argc, char* argv[]) {
  Window GameWindow;
  bool running = true;
  SDL_Event event;

  while (running) {
    while (SDL_PollEvent(&event)) {
      if (event.type == SDL_QUIT) {
        running = false;
      }
    }
    GameWindow.HandleKeyboard();
    // Rendering code here
  }
  
  return 0;
}
Neither W nor A keys pressed
W key is pressed
W and A keys are pressed

Explanation

  • SDL_GetKeyboardState(): This function returns a pointer to an array of key states.
  • Key States: Each element in the array represents the state of a key. If the key is pressed, the value is 1 (true). If not, the value is 0 (false).
  • Simultaneous Checks: You can check multiple keys simultaneously by querying the array at different indices corresponding to the keys you are interested in.

Tips

  • Key Indexing: Use SDL’s predefined scan codes like SDL_SCANCODE_W and SDL_SCANCODE_A to index into the keyboard state array.
  • Polling: Ensure you call SDL_PollEvent() or SDL_PumpEvents() in your loop to keep the keyboard state updated.

This approach allows you to handle complex input scenarios where multiple keys might be pressed simultaneously, such as in games or other interactive applications.

This Question is from the Lesson:

Understanding Keyboard State

Learn how to detect and handle keyboard input in SDL2 using both event-driven and polling methods. This lesson covers obtaining and interpreting the keyboard state array.

Answers to questions are automatically generated and may not have been reviewed.

This Question is from the Lesson:

Understanding Keyboard State

Learn how to detect and handle keyboard input in SDL2 using both event-driven and polling methods. This lesson covers obtaining and interpreting the keyboard state array.

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