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Hello Everyone,

I just started off with some openglProgramming.

I am using the Tao OpenGL library.

Here is my question:

When I am drawing rectangles in 2d, do I always have to re-draw old rectangles?
or is there a way that I draw only new ones?

What I am doing here is:

Gl.glViewport(0, 0, Me.Width, Me.Height)
Gl.glClearColor(0.5F, 0.5F, 0.5F, 0.5F)
Dim r = 45
Gl.glOrtho(-r, r, -r * (_height / _width), r * (_height / _width), -r, r)
Gl.glColor3f(1.0F, 0.5F, 0.5F)
Gl.glVertex2f(0, 10)
Gl.glVertex2f(10, 10)
Gl.glVertex2f(10, 20)
Gl.glVertex2f(0, 20)

And when I draw again, I need to re-run this code...
So is it necesssary to re-draw or is there another way out?

Posted 9-Aug-12 23:29pm
Volynsky Alex at 10-Aug-12 5:47am
Please see here:
videepmishraa at 10-Aug-12 6:16am
The video is a nice demonstration. But that has been done with GDI+ and I am trying to do it with OpenGL.
The reason I am using OpenGL is because when I draw rectangles, I want to change their properties too!!!

1 solution

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Solution 1

Unless you draw to some other surface that, itself, can be drawn to the screen, yes, you have to redraw everything. Why? Because if you drag another window acrossed your drawing surface everything will get overwritten on screen and have to be redrawn when the surface come back into view.

It doesn't matter which drawing API you use, GDI or OpenGl, the concepts are still the same.
videepmishraa at 14-Aug-12 5:51am
Thank You,
I have another question:
How to make a surface which can re-draw it from time to time?


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