Change window color after color is picked

OpenGL OpenGL: Basic Coding
1

I am working on a color picking program with two windows.
There’s a cube (from which you pick the color) in the main window. Once the user picks a color, the second window has to make it’s background color into the color that was picked.
I use

glReadPixels()

to get the color. I have a global char array that stores this color.
I know this is working because I display the color’s RGB value in the console window and the correct values are printed.
In the new window, other than the initialization things, all I have is a

glClearColor()

in the display function. The values in the glClearColor are from the global array that I mentioned earlier. So, (with my limited knowledge) I am not sure where I’m going wrong.
The color in the new window is always black and never changes to the picked color.

How can I fix this?

2

Are you actually clearing the window? I.e. are you calling glClear in the display function, and is the display function actually being called for that window?

3

The display function is for the second window.
But I don’t call glClear in it (I call glClearColor)

4

glClearColor sets the clear colour which glClear uses to clear the window. You need to call glClear; and unless the toolkit does it automatically, you also need to swap buffers (glutSwapBuffers or similar).

5

Ahh I didn’t know that.

void colorDisplay()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glFlush();
glClearColor((int)pixel[0], (int)pixel[0], (int)pixel[0], 0.0f);
glutSwapBuffers();
}

This is my function now.
I use the same glClear in my other display function.

6

Adding the glClear did not help

7

For one thing, you should call glClearColor before glClear. glClearColor itself doesn’t do anything except set the colour to be used by a subsequent glClear call.

The other thing: is the display function actually getting called for the other window? Add a print statement or set a debugger breakpoint to confirm. With GLUT, you should probably be calling glutSetWindow followed by glutPostRedisplay to force it to be redrawn.

8

I got it to work.
Turns out I never reset the window to the second one using glutSetWindow().

Thanks for the help