Drawing GUIs is usually done by drawing textured rectangular polygons (quads) to the screen (as you said). glOrtho sets the projection matrix to a 2d projection. The projection matrix basically contains the perspective transformation, but since a GUI has no perspective (generally) glOrtho "removes" it.

You could use it like this;

glMatrixMode(GL_PROJECTION);glOrtho(0.0f, 4.0f, 0.0f, 3.0f, 0.0f, 1.0f);glMatrixMode(GL_MODELVIEW);// draw rectangular textured quads hereglBegin(GL_QUADS);    glTexCoord2f(tc1, tc2);    glVertex2f(x, y);    // etc...glEnd();    

The x coordinate goes from 0 (left) to 4 (right), the y coordinate goes from 0 (bottom) to top (3).

I included a glOrtho description for reference:

=======================================The glOrtho function multiplies the current matrix by an orthographic matrix.void glOrtho(    GLdouble left, 	    GLdouble right, 	    GLdouble bottom, 	    GLdouble top, 	    GLdouble near, 	    GLdouble far 	   );	 Parametersleft, rightThe coordinates for the left and right vertical clipping planes. bottom, topThe coordinates for the bottom and top horizontal clipping planes. near, farThe distances to the nearer and farther depth clipping planes. These distances are negative if the plane is to be behind the viewer.=======================================   

I hope this helps

EDIT: I missed the mouse part

You need to get a hold of the mouse coordinates. There are various ways to do so and many are platform dependent. I'll assume Windows.

In the windows messaging loop, the giant switch statements, add this (make sure there are two global ints in your program called xPos and yPos):

case WM_MOUSEMOVE:    // the mouse has moved; windows is telling you where to.    // this is in screen coordinates (pixels of window), counted from the upper left    xPos = LOWORD(lParam);  // horizontal position of cursor     yPos = HIWORD(lParam);  // vertical position of cursor     break;case WM_LBUTTONUP:case WM_RBUTTONUP:    // the user clicked at (xPos, yPos)    xPos = LOWORD(lParam);  // horizontal position of cursor     yPos = HIWORD(lParam);  // vertical position of cursor     // check which button got clicked    break;  

Just determine whether the user clicked on a botton or not... you should be able to continue from here. I suggest looking up the windows documentation on the above windows messages.


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[edited by - Kurioes on April 20, 2004 5:19:26 PM]