Question

What I want is to be able to change the value of a variable through the window with the graphics, not from the code. It’s ok if there are several fixed values and there is a choice only between them. Can you please give me some ideas?

I was thinking of something like this:
|–|–|–|–|–|, where each vertical line repesents a value and when you click the line, the value is changed, but it’s a bit difficult for me to implement this. Any simpler ideas

Answer 1

Here’s a quick keyboard-based solution (I’m assuming C++):

Let’s assume your values are all in an array called values:

const int NUM_VALUES = 5;
int values[NUM_VALUES];

Keep track of the selected value:

int selectionIndex = 0;

Make a function to handle key presses:

void keyPressed (unsigned char key, int x, int y) { 
    if (key == GLUT_KEY_LEFT) {
        if(--selectionIndex < 0)
            selectionIndex = NUM_VALUES - 1;
    } 
    else if (key == GLUT_KEY_RIGHT) {
        if(++selectionIndex >= NUM_VALUES)
            selectionIndex = 0;
    }  
    else if (key == GLUT_KEY_UP) {
        values[selectionIndex]++;
    }  
    else if (key == GLUT_KEY_DOWN) {
        values[selectionIndex]--;
    }   
}

Finally, in your initialization, link keyPressed to glutKeyboardFunc:

glutKeyboardFunc(keyPressed);