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I'm having some trouble understanding how I should conditionally render shapes. For example, say I want to render a 3d object based upon the push of a button - how am I suppose to handle that? I haven't really been able to find example code or tutorials for something like this, so I'm curious about what the best practices are for this.

Now, I've done a lot of searching online and I've found the use of timers to handle things, but I'm not sure if I should use a timer here. For example, I was thinking I should use a timer to call a method, say its named renderScene, that determines what to render based upon some booleans that are set by other methods called on button presses. So, basically when you push a button, you set a boolean to be true, and thats picked up by renderScene which is called through the use of a timer. renderScene then goes ahead and calls updateGL and the scene is updated.

Is that the way I should approach this, or is there a better way? I feel like that's probably not the correct solution, so I was reaching out.

genpfault
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user3675085
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1 Answers1

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Conditionally rendering geometry in opengl is as simple as tracking a boolean and to omit or emit the corresponding draw-calls accordingly. The only thing required is that you redraw the scene in respect to your windowing framework of choice. If you don't need to redraw at periodic intervals; simply trigger the redraw a single time after every change. Alledgedly update triggers the paintGL event (see also: How to force QGLWidget to update screen?).

Community
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Lawrence Kok
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  • I would add that you should keep in mind some certain draw characteristics like blending, transparency, and any projection variations when doing conditional drawing. Exactly as suspected, and as answered, you simply apply a boolean check to see if conditions are met for drawing, but also make sure that the conditional sections contain all the necessary blending information or texture information to turn on, or off, as necessary. The best option is self-contained draw methods, then use the booleans to check on calling those self-contained methods, so all the conditions are consistent. –  Aug 02 '14 at 07:29