Managing Window Position

Window Edge Snapping

How can I make my window snap to the edges of the screen like in Windows?

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Edge snapping (sometimes called "aero snap") is a popular window management feature that we can implement using SDL. Here's how to create basic edge snapping functionality:

Basic Edge Detection

First, we need to detect when a window is near a screen edge:

1#include <SDL.h>
2#include <cmath> // for std::abs
3
4bool IsNearEdge(
5  int Position, int Edge, int SnapDistance = 20
6) {
7  return std::abs(Position - Edge) < SnapDistance;
8}
9
10void HandleWindowMove(SDL_Window* Window) {
11  // Get current window position
12  int WinX, WinY;
13  SDL_GetWindowPosition(Window, &WinX, &WinY);
14
15  // Get screen dimensions
16  SDL_DisplayMode Display;
17  SDL_GetCurrentDisplayMode(0, &Display);
18
19  // Check if near any edge
20  if (IsNearEdge(WinX, 0)) { 
21    // Snap to left
22    SDL_SetWindowPosition(Window, 0, WinY);                
23  } else if (IsNearEdge(WinX + 800, Display.w)) { 
24    // Snap to right
25    SDL_SetWindowPosition(
26      Window, Display.w - 800, WinY);
27  }
28}

Complete Snapping Implementation

Here's a more complete implementation that handles all edges and corners:

1#include <SDL.h>
2#include <cmath>
3
4class Window { /*...*/ };
54
55int main(int argc, char** argv) {
56  SDL_Init(SDL_INIT_VIDEO);
57  Window GameWindow;
58  SDL_Event E;
59
60  while (true) {
61    while (SDL_PollEvent(&E)) {
62      if (
63        E.type == SDL_WINDOWEVENT &&
64        E.window.event == SDL_WINDOWEVENT_MOVED
65      ) {
66        GameWindow.SnapToEdges(); 
67      }
68    }
69  }
70
71  SDL_Quit();
72  return 0;
73}

This implementation provides a smooth snapping effect when the window gets near any screen edge. The SnapDistance constant determines how close to an edge the window needs to be before it snaps. You can adjust this value to make the snapping more or less sensitive.

Remember that this is a basic implementation - commercial window managers often include additional features like partial screen snapping (half-screen, quarter-screen) and multi-monitor support.

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