2D games programming coordinates in C

Question

I'm making my way through some ncurses tutorials as I want to improve some of my C programming skills. I'm at a point where the tutorial is emulating a simple tennis game.

What confuses me is this:

* think of posX as relating to rows, the bottom of the screen will be at
maximum Y value, so subtract 2, to set the racket near the bottom */
p.posX = SCREEN_HEIGHT - 2;

/* think of posY as relating to a column, the middle of the screen will be
at the middle of the screen_width, divided by 2, to set racket at center */
p.posY = SCREEN_WIDTH / 2;

and say, the racket is moved left by the user:

void moveRacketLeft() {
if (p.posY - 2 > 0) { // ensure racket is still on screen
    mvprintw(p.posX, p.posY-1, "   ");  // if true, it will print an empty space, deleting the racket
    p.posY --;    // remember to decrement, as we are going to the left
    }

}

What confuses me about this, is that the X and Y positions have seem to be reversed and I don't know how to logically 'get it'.

Is there some kind of grey area between conventional coordinates in C programming and the use of the ncurses library? Or is the tutorial making a mistake?

Many thanks

Answer 1

The x and y coordinates in curses are as you expect: x is the horizontal coordinate, corresponding to columns. y is the vertical coordinate, cooresponding to rows.

But in curses, these coordinates are usually given in the order y, x. For example, the prototype to mfprintw mentioned in your code snippet is:

int mvprintw(int y, int x, const char *fmt, ...);

And there are even functions (or macros. rather) that have yx in their name, e.g. getyx.

I imagine that this notation was chosen, because it reflects the way that two-dimensional arrays are addressed in C: array[row][col].