Bitwise vs Logical Operators
Why do we use bitwise operators (| and &) for window flags instead of regular boolean operators (|| and &&)?
The use of bitwise operators for window flags is related to how SDL stores multiple configuration options efficiently in a single integer. Let's explore why this works:
How Window Flags Work
Each flag is represented by a single bit in an integer:
#include <SDL.h>
#include <iostream>
#include <bitset>
int main() {
// Let's look at the actual bits of
// some window flags
std::cout << "\nFullscreen: "
<< std::bitset<32>(SDL_WINDOW_FULLSCREEN);
std::cout << "\nBorderless: "
<< std::bitset<32>(SDL_WINDOW_BORDERLESS);
std::cout << "\nResizable: "
<< std::bitset<32>(SDL_WINDOW_RESIZABLE);
}Fullscreen: 00000000000000000000000000000001
Borderless: 00000000000000000000000000010000
Resizable: 00000000000000000000000000100000Combining Flags
When we want multiple flags, we use the bitwise OR operator (|) to set multiple bits:
#include <SDL.h>
#include <iostream>
#include <bitset>
int main() {
auto Flags{
SDL_WindowFlags(
SDL_WINDOW_BORDERLESS |
SDL_WINDOW_RESIZABLE
)};
std::cout << "Combined: "
<< std::bitset<32>(Flags);
}Combined: 00000000000000000000000000110000If we used the logical OR operator (||) instead:
#include <SDL.h>
#include <iostream>
#include <bitset>
int main() {
auto Flags{
SDL_WindowFlags(
SDL_WINDOW_BORDERLESS ||
SDL_WINDOW_RESIZABLE
)};
std::cout << "Combined: "
<< std::bitset<32>(Flags);
}Bad Combo: 00000000000000000000000000000001The logical operator would just give us 1 (true) or 0 (false), losing the ability to store multiple flags!
Checking Flags
Similarly, we use the bitwise AND operator (&) to check if specific bits are set:
#include <SDL.h>
#include <iostream>
int main() {
SDL_Init(SDL_INIT_VIDEO);
SDL_Window* Window{SDL_CreateWindow(
"Flag Example",
100, 200, 600, 300,
SDL_WINDOW_BORDERLESS | SDL_WINDOW_RESIZABLE
)};
auto Flags{SDL_WindowFlags(
SDL_GetWindowFlags(Window))};
// Correct way to check flags
bool HasBorder{!(Flags & SDL_WINDOW_BORDERLESS)};
// Wrong way - would just check if either
// value is non-zero
bool BadCheck{Flags && SDL_WINDOW_BORDERLESS};
std::cout << "Has Border: " << HasBorder;
std::cout << "\nBad Check: " << BadCheck;
SDL_DestroyWindow(Window);
SDL_Quit();
return 0;
}This bit manipulation approach is very memory efficient and fast, which is why it's commonly used in systems programming and game development.
Window Configuration
Explore window creation, configuration, and event handling using SDL's windowing system