Calculating Mouse Pointer Angle
How can I get the mouse pointer's angle relative to a position on the screen?
Here's a simple example that shows how querying mouse state can be useful. We'll create an object that reports the direction from the center of the window to the mouse cursor when the space bar is pressed.
First, let's create a constructor that receives an SDL_Window*, and stores where the center of the window is:
#include <SDL.h>
#include <iostream>
#include "Window.h"
class DirectionTracker {
public:
DirectionTracker(SDL_Window* Window) {
int windowWidth, windowHeight;
SDL_GetWindowSize(Window, &windowWidth,
&windowHeight);
centerX = windowWidth / 2;
centerY = windowHeight / 2;
std::cout <<
"Window center initialized at: ("
<< centerX << ", " << centerY << ")\n";
}
private:
int centerX, centerY;
};
int main(int argc, char** argv) {
SDL_Init(SDL_INIT_VIDEO);
Window GameWindow;
DirectionTracker Tracker{
GameWindow.SDLWindow};
SDL_Event Event;
while (true) {
while (SDL_PollEvent(&Event)) {
// ...
}
GameWindow.Update();
}
SDL_Quit();
return 0;
}Window center initialized at: (350, 150)Next, when our event loop detects the user pressing the space bar, we'll notify the DirectionTracker:
#include <SDL.h>
#include <iostream>
#include "Window.h"
class DirectionTracker {
public:
DirectionTracker(SDL_Window*){/*...*/}
void KeyboardEvent(SDL_KeyboardEvent& e) {
if (e.type == SDL_KEYDOWN
&& e.keysym.sym == SDLK_SPACE) {
ReportAngle();
}
}
private:
void ReportAngle() {
std::cout << "TODO: Report Angle";
}
int centerX, centerY;
};
int main(int argc, char** argv) {
SDL_Init(SDL_INIT_VIDEO);
Window GameWindow;
DirectionTracker Tracker{
GameWindow.SDLWindow};
SDL_Event Event;
while (true) {
while (SDL_PollEvent(&Event)) {
if (Event.type == SDL_KEYDOWN) {
Tracker.KeyboardEvent(Event.key);
}
}
GameWindow.Update();
}
SDL_Quit();
return 0;
}Window center initialized at: (350, 150)
TODO: Report AngleThe final step is to complete the ReportAngle() function. We query the mouse position using SDL_GetMouseState(), and implement the required calculations to determine its direction from the center of the screen:
#include <SDL.h>
#include <iostream>
#include "Window.h"
class DirectionTracker {
public:
DirectionTracker(SDL_Window*){/*...*/}
void KeyboardEvent(SDL_KeyboardEvent&){/*...*/}
private:
void ReportAngle() {
// Get current mouse position
int mouseX, mouseY;
SDL_GetMouseState(&mouseX, &mouseY);
// Calculate direction from center to mouse
int dirX = mouseX - centerX;
int dirY = mouseY - centerY;
// Calculate angle in degrees
double angle{
atan2(dirY, dirX) * 180.0 / M_PI};
std::cout << "\nDirection from center: "
<< dirX << ", " << dirY
<< " (angle: " << angle << " degrees)";
}
int centerX, centerY;
};
int main(int argc, char** argv){/*...*/}
Window center initialized at: (350, 150)
Direction from center: -228, -77 (angle: -161.339 degrees)
Direction from center: 248, 113 (angle: 24.4962 degrees)Mouse State
Learn how to monitor mouse position and button states in real-time using SDL's state query functions