Calculate Mouse Position

How can I calculate the distance of the mouse cursor from the edges of the window?

Calculating the distance of the mouse cursor from the edges of the SDL window is straightforward. You need to know the current position of the mouse cursor and the dimensions of the window.

Step-by-Step Guide

  1. Get Mouse Position: Capture the current position of the mouse cursor using SDL events.
  2. Get Window Dimensions: Retrieve the dimensions of the SDL window.
  3. Calculate Distances: Use basic arithmetic to calculate the distances from each edge of the window.

Example Code

Here's a complete example demonstrating how to calculate the distance of the mouse cursor from the edges of the window:

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

void CalculateMouseDistances(
  int mouseX, int mouseY,
  int windowWidth, int windowHeight
) {
  int distanceFromLeft = mouseX;
  int distanceFromTop = mouseY;
  int distanceFromRight = windowWidth - mouseX;
  int distanceFromBottom = windowHeight - mouseY;

  std::cout << "Distance from left: "
    << distanceFromLeft << '\n';      
  std::cout << "Distance from top: "
    << distanceFromTop << '\n';        
  std::cout << "Distance from right: "
    << distanceFromRight << '\n';    
  std::cout << "Distance from bottom: "
    << distanceFromBottom << '\n';  
}

int main(int argc, char* argv[]) {
  if (SDL_Init(SDL_INIT_VIDEO) != 0) {
    std::cerr << "SDL_Init Error: "
      << SDL_GetError() << '\n';
    return 1;
  }

  SDL_Window* window = SDL_CreateWindow(
    "Mouse Distance Calculation",
    100, 100, 640, 480, SDL_WINDOW_SHOWN);
  if (window == nullptr) {
    std::cerr << "SDL_CreateWindow Error: "
      << SDL_GetError() << '\n';
    SDL_Quit();
    return 1;
  }

  int windowWidth, windowHeight;
  SDL_GetWindowSize(
    window, &windowWidth, &windowHeight);

  SDL_Event event;
  bool running = true;
  while (running) {
    while (SDL_PollEvent(&event)) {
      if (event.type == SDL_QUIT) {
        running = false;
      } else if (event.type == SDL_MOUSEMOTION) {
        int mouseX = event.motion.x;
        int mouseY = event.motion.y;
        CalculateMouseDistances(
          mouseX, mouseY,
          windowWidth, windowHeight
        );
      }
    }
  }

  SDL_DestroyWindow(window);
  SDL_Quit();
  return 0;
}
Distance from left: 100
Distance from top: 150
Distance from right: 540
Distance from bottom: 330

Explanation

  • Initialization: SDL is initialized, and a window is created.
  • Window Size: SDL_GetWindowSize() retrieves the width and height of the window.
  • Event Loop: The event loop captures SDL_MOUSEMOTION events to get the current position of the mouse cursor.
  • Distance Calculation: The CalculateMouseDistances() function computes the distances from the mouse cursor to each edge of the window using simple arithmetic.

Calculations

  • Distance from Left: mouseX
  • Distance from Top: mouseY
  • Distance from Right: windowWidth - mouseX
  • Distance from Bottom: windowHeight - mouseY

Summary

By combining the current mouse position with the window dimensions, you can easily calculate the distance from the mouse cursor to any edge of the window.

This technique is useful for implementing features like edge scrolling or snapping UI elements to window edges.

Mouse Input Basics

Discover how to process mouse input, including position tracking and button presses

Questions & Answers

Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

SDL Coordinate System: Why Y-Down?
Why does SDL use a y-down coordinate system instead of y-up?
SDL: Get Mouse Screen Coordinates
Can I get mouse coordinates relative to the screen instead of the window?
SDL_PollEvent() vs SDL_WaitEvent()
What's the difference between SDL_PollEvent() and SDL_WaitEvent()?
SDL Event Timestamp Field
What does the timestamp field in the event structures mean?
SDL Event which Field
What does the which field in the event structures refer to (e.g., multiple mice)?
SDL: Custom Mouse Cursor Appearance
Can I change the mouse cursor's appearance (e.g., to a crosshair)?
SDL Double Click Timing Customization
How does SDL determine the time window for registering a double click? Can I customize this timing?
Retrieve Mouse Position
How do I retrieve the current position of the mouse cursor in SDL?
SDL Mouse Motion Events
What is the difference between SDL_MOUSEMOTION and SDL_MouseMotionEvent?
Detect Double Clicks in SDL
How can I detect double clicks using SDL?
SDL_MouseButtonEvent Structure
What is the SDL_MouseButtonEvent structure used for?
Or Ask your Own Question
Get an immediate answer to your specific question using our AI assistant