Thread: how to create a sliding bar in opengl?

anyone got any sample code on how to create a sliding bar in opengl?

i try looking on the net, couldn't find one.

thanks alot in advance

u know those u adjust to the left and right to achieve different values
something like a scroll bar on the right of the IE browser

well depending on a couple factors a very general outline is like this:

1. create a textured polygon that is your slide background
2. create a textured polygon that is the slide
3. put them where you want them
4. set the precision or whatever you call it the number of possible value positions the slider can have
5. calculate the pixel to precision ratio
6. set the slide at its default position based on the default value
7. when clicked have the slide follow the mouse horizontally or vertcially to the limits of the slide, and snap it to position wherever it is when the mouse button is let up. or if the slide is not clicked but the slide background is, either have the slide jump to that position or move towards it.
8. calculate the value based on the new position of the slide

also remember to calculate room at ends of the background to account for the slide, so it doesn't go over the edge...
you could create a third polygon that represents the "groove" to make it easier to keep the slide in bounds.

thanks
did a pretty simple one, but enough for my case

Originally Posted by no-one

well depending on a couple factors a very general outline is like this:

1. create a textured polygon that is your slide background
2. create a textured polygon that is the slide
3. put them where you want them
4. set the precision or whatever you call it the number of possible value positions the slider can have
5. calculate the pixel to precision ratio
6. set the slide at its default position based on the default value
7. when clicked have the slide follow the mouse horizontally or vertcially to the limits of the slide, and snap it to position wherever it is when the mouse button is let up. or if the slide is not clicked but the slide background is, either have the slide jump to that position or move towards it.
8. calculate the value based on the new position of the slide

also remember to calculate room at ends of the background to account for the slide, so it doesn't go over the edge...
you could create a third polygon that represents the "groove" to make it easier to keep the slide in bounds.

now i come to another problem
i want to create a another window for the sliding bar itself

how do i do it?

you mean another Window's type window? and have them communicate? that, lies outside of my realm of expertise.

In OpenGL you wouldn't have to make each object a window as you do in true Windows programming. Most of the same thing can be 'simulated' by clever use of textured quadrilaterals. Note that you can also use alpha blending to achieve some affects that Window's GUIs still can't do very well.

You could create your own window's class. Create a default type of WndProc() for your window and make it virtual.

If the user does not re-define WndProc() relative to the window he creates by deriving from the base Window class, then all messages will go to your WndProc().

But sending messages to the WndProc() is quite simple as well as is tracking the mouse, keyboard, etc.

You can use the same exact setup that Windows uses or you can create your own. But you don't have to use the RegisterClass() methodology with this setup....I think that would be too much.

Code:

#include <queue.h>

struct MSG
{
  DWORD msg;
  Vector2 MousePos;
};

class CWindow
{
   protected:
   
    public:
      CWindow(void) {}
      queue<MSG> MessageQueue;

      virtual int WndProc(MSG pMsg,WORD lParam,WORD wParam);

      //Text functions
      //Caret functions
      //Window access functions
      //Window drawing functions
      //Message functions
      //etc, etc.
};


//Static objects
class CStatic:public CWindow
{
}

class CBitmap:public CStatic
{
}

class CText:public CStatic
{
}


//Button objects
class CButton:public CWindow
{
}

class CRadioButton:public CButton
{
}

class CCheckBox:public CButton
{
}

//Edit controls
class CEdit:public CWindow
{
}

//Listboxes
class CListBox:public CWindow
{
}

class CListBoxCtrl:public CListBox
{
}

//the sky is the limit

With this type of setup you can do a pretty rudimentary Windows type GUI with little trouble.

The most important class in the framework is CWindow. Almost all window functionality ever needed should be in this class.

If you do choose to use the RegisterClass setup then you can be assured that every window in the system will have a message queue because you have given it one. When an event happens and you need to send a message you post the message to the queue or you can directly call the window's WndProc with the message. Messages are passed along from the parent window object to its children and/or to its controls. You can create dialog boxes and all kinds of stuff if you really sit down and think it through.

Also if you understand a bit about Win32 programming then you should be able to emulate this in a graphical environment like OpenGL. The benefit to this is that most of us are quite familiar with Win32 programming and so using your GUI system would be a snap.

If you want to know the truth I look for Windows to be ported to using 3D graphics and textured quads in the future. 3D cards are much faster and the interface looks much jazzier. Plus you don't have to worry about DC's (except with printers, etc) and it would be a lot easier to use graphics in the API. Maybe I'm wrong, but I think Microsoft should move the entire GUI into Direct3D and dump the 2D stuff.