Viewport boundaries on any resolution with OpenGL ES

Question

I'm having difficulties understanding about the OpenGL perspective view. I've read tons of information however it didn't help me trying to achieve what I'm after. Which is making sure my 3d scene is filling the entire screen on every Android device.

To test this, I will be drawing a quad in 3d space which in the end should touch every corner, filling up the whole device's screen. I could then use this quad, or actually its coordinates to specify a bounding box at a certain Z distance which I could use to put my geometry and making sure those fill up my screen. When the screen resizes, or I am to run it on another screen resolution, I would recalculate this bounding box and geometry. I'm not talking about static geometry, but for instance say I want to fill the screen with balls and it doesn't matter how big or how many balls there are, the only important thing is the screen is filled and there are no redundant balls outside the visible frustum.

• As far as I understand when specifying the viewport you actually bind pixel values to the frustum's boundaries. I know that you can actually set an orthographic view in a way your window pixels match 3d geometry position but I'm not sure how this works in perspective view.
• Here I'm assuming the viewport width and height to be mapped to the nearZ. So when a ball is at Z=1f it has it's original size
• When moving the ball into the screen so into the direction of farZ, the ball would be scaled down in order for the perspective to work. So a ball at Z=51f for instance, would appear smaller on my screen and I would need more balls to fill up the entire screen.
• Now in order to do so, I'm looking for the purple boundaries
• Actually I need these boundaries to fill the entire screen on different frustum sizes (width x height) while the frustum angle and Z distance for the balls is always the same
• I guess I could use trig to calculate these purple boundaries (see blue triangle note)
• Am I correctly marking the frustum angle, it being the vertical angle of the frustum?
• Could someone elaborate on the green 1f and -1f values as I seem to have read something about it? Seems like some scalar that is used to resize the geometry within the frustum?

I actually want to be able to programmaticaly position geometry against the viewport borders within 3d space at any resolution/window for any arbitrary Android device.

Note: I have a flash background which uses a stage (visual area) with a known width x height at any resolution which makes it easy to position/scale assets either using absolute measurements or percentual measurements. I guess I'm trying to figure out how this system applies to OpenGL's perspective view.

Answer 1

I guess this post using gluUnproject answers the question.