Is there a way to disable auto-capture for specific mouse buttons but keep it for others?

Question

Ryan McCombe · Accepted Answer

SDL's auto-capture feature is controlled through the SDL_HINT_MOUSE_AUTO_CAPTURE hint, but it doesn't provide direct per-button control. However, we can implement our own selective auto-capture system by disabling the built-in auto-capture and managing it ourselves.

Here's a complete implementation that demonstrates this approach:

1#include <SDL.h>
2#include <bitset>
3#include <iostream>
4
5class SelectiveMouseCapture {
6public:
7  SelectiveMouseCapture() {
8    // Disable SDL's built-in auto-capture
9    SDL_SetHint(
10      SDL_HINT_MOUSE_AUTO_CAPTURE, "0"); 
11  }
12
13  void
14    EnableAutoCaptureForButton(Uint8 button) {
15    if (button < MaxButtons) {
16      autoCaptureButtons.set(button);
17    }
18  }
19
20  void
21    DisableAutoCaptureForButton(Uint8 button) {
22    if (button < MaxButtons) {
23      autoCaptureButtons.reset(button);
24    }
25  }
26
27  void HandleMouseDown(
28    SDL_MouseButtonEvent& event) {
29    if (event.button < MaxButtons &&
30      autoCaptureButtons.test(event.button)) {
31      SDL_CaptureMouse(SDL_TRUE);
32      isCapturing = true;
33    }
34  }
35
36  void HandleMouseUp(
37    SDL_MouseButtonEvent& event) {
38    if (isCapturing && event.button < MaxButtons
39      &&
40      autoCaptureButtons.test(event.button)) {
41      SDL_CaptureMouse(SDL_FALSE);
42      isCapturing = false;
43    }
44  }
45
46private:
47  static const size_t MaxButtons = 32;
48  std::bitset<MaxButtons> autoCaptureButtons;
49  bool isCapturing = false;
50};
51
52int main(int argc, char** argv) {
53  SDL_Init(SDL_INIT_VIDEO);
54  SDL_Window* window =
55    SDL_CreateWindow("Selective Capture",
56                     SDL_WINDOWPOS_CENTERED,
57                     SDL_WINDOWPOS_CENTERED,
58                     800, 600,
59                     SDL_WINDOW_SHOWN);
60
61  SelectiveMouseCapture captureManager;
62
63  // Enable auto-capture for left button only
64  captureManager.EnableAutoCaptureForButton(
65    SDL_BUTTON_LEFT); 
66
67  bool running = true;
68  while (running) {
69    SDL_Event event;
70    while (SDL_PollEvent(&event)) {
71      if (event.type == SDL_QUIT) {
72        running = false;
73      } else if (event.type ==
74        SDL_MOUSEBUTTONDOWN) {
75        captureManager.HandleMouseDown(
76          event.button);
77        std::cout << "Button "
78          << (int)event.button.button
79          << " pressed\n";
80      } else if (event.type == SDL_MOUSEBUTTONUP) {
81        captureManager.HandleMouseUp(
82          event.button);
83        std::cout << "Button "
84          << (int)event.button.button
85          << " released\n";
86      }
87    }
88
89    // Show capture state
90    bool isCaptured = SDL_GetWindowFlags(window)
91      & SDL_WINDOW_MOUSE_CAPTURE;
92    std::cout << "Capture State: " << (
93        isCaptured ? "Active" : "Inactive")
94      << "\r" << std::flush;
95  }
96
97  SDL_DestroyWindow(window);
98  SDL_Quit();
99  return 0;
100}

You can configure which buttons should trigger auto-capture:

1SelectiveMouseCapture captureManager;
2
3// Example configurations:
4// Only left button auto-captures
5captureManager.EnableAutoCaptureForButton(
6  SDL_BUTTON_LEFT);
7
8// Left and right buttons auto-capture
9captureManager.EnableAutoCaptureForButton(
10  SDL_BUTTON_LEFT);
11captureManager.EnableAutoCaptureForButton(
12  SDL_BUTTON_RIGHT);
13
14// Disable auto-capture for middle button
15captureManager.DisableAutoCaptureForButton(
16  SDL_BUTTON_MIDDLE);

This implementation offers several advantages:

Fine-grained control over which buttons trigger auto-capture
Clean separation of capture management logic
Easy to modify or extend the behavior
Maintains proper capture state tracking

Key considerations when using selective auto-capture:

Remember to handle focus loss appropriately
Consider adding visual feedback for capture state
Be mindful of button combinations
Test thoroughly with different input scenarios

Mouse Capture and Global Mouse State

Selective Mouse Button Auto-Capture

Mouse Capture and Global Mouse State

Game Development with SDL2

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