OpenGL viewport aspect ratio

Monkey Forums/Monkey Programming/OpenGL viewport aspect ratio

Grant

(Posted 2013) [#1]

Hi all,

I have been messing about with openGL module for monkey, Everything seems fine except for 1 thing, How on earth do you set the aspect ratio to avoid the dreaded stretching of drawn objects?

I have googled and I am getting nowhere, surely it must be possible to change the aspect so objects are drawn properly but it's not at all obvious, can someone please help me :)

Cheers, Grant.

therevills

(Posted 2013) [#2]

Have a look at AutoFit ;)

Grant

(Posted 2013) [#3]

Thanks therevills,

I use the lovely autofit regular but sadly it's not what I'm looking for this time around. I want everything to run at the device native resolution and be independent of physical aspect ratios, no borders, OpenGL viewport with perspective rendering.

IIRC from doing similar in XNA It's something to do with the view or projection matrix and a homogeneous viewport.

Cheers, Grant.

YAY, fixed!!! setting the aspect in glFrustumf done the damage :)

charlie

(Posted 2013) [#4]

isn't it just window width/height?

Cheers
Charlie

Grant

(Posted 2013) [#5]

Hi charlie,

Almost dude,

glViewport (0,0,DeviceWidth(),DeviceHeight())
glMatrixMode( GL_PROJECTION )
glLoadIdentity()
glFrustumf(-1.0,1.0,0.0-Float(DeviceHeight())/Float(DeviceWidth())),Float(DeviceHeight())/Float(DeviceWidth()),1.0,30.0)

cheers, Grant.

Sammy

(Posted 2013) [#6]

A little bit confused here, what does the above code actually do to the viewport?

Grant

(Posted 2013) [#7]

It's setting the clipping planes according to dimensions described by the floats, think of it as describing the shape you would see projected in space, a kind of distorted cube or pyramid with the top chopped of that describes the volume everything is rendered in. you need to tell opengl the shape of the window or screen so it can adjust this crazy pyramid to prevent stretching of rendered objects. Any ratio, any pixel aspect is catered for, some hardware uses non square pixels, so the viewport settings do not always describe the shape of the screen or window.

left, right, bottom, top, near, far clipping planes.

I'm assuming a 1:1 pixel aspect ratio (square pixels) in this code.

cheers, grant.

Sammy

(Posted 2013) [#8]

Ah, now I see, thanks for that explanation Grant.