Vertex Transformation wiki page

OpenGL OpenGL: Basic Coding
1

Hi,

While learning about vertex transformations I have found a page in the OpenGL wiki which explains them with numbers. I tried to reproduce them but failed. Then I checked using glGet functions and found that projection matrix shown on the page is wrong.

Since I am new to OpenGL can someone with more experience check the numbers on that page.

Page at OpenGl wiki: Vertex Transformation

Projection matrix should be:

	[     10.00000,      0.00000,      0.00000,      0.00000 ]
	[      0.00000,      1.81818,      0.81818,      0.00000 ]
	[      0.00000,      0.00000,     -1.00200,     -2.00200 ]
	[      0.00000,      0.00000,     -1.00000,      0.00000 ]

Is this correct?

Thank you

2

The matrix you give is correct for the glFrustum() call on the wiki page.

The matrix on the wiki page is correct for the call


glFrustum(-1.0, 0.1, -0.1, 0.1, 1.0, 1000.0)

Neither version seems to make much sense, one of the edges is at 45 degrees, while the other three are at 2.86 degrees. I.e. the projection is heavily off-centre with a fairly extreme aspect ratio.

I suspect that the first four values should have been either ±0.1 or ±1.0. Either would result in a centred projection with a 1:1 aspect ratio, but 0.1 is a rather narrow field of view (closer to telephoto zoom or sniper scope than to normal vision).

3

Thanks,

If no one complains I will update wiki page with my results:

projection matrix:
	[     10.00000,      0.00000,      0.00000,      0.00000 ]
	[      0.00000,      1.81818,      0.81818,      0.00000 ]
	[      0.00000,      0.00000,     -1.00200,     -2.00200 ]
	[      0.00000,      0.00000,     -1.00000,      0.00000 ]
model view matrix:
	[      1.00000,      0.00000,      0.00000,      1.00000 ]
	[      0.00000,      1.00000,      0.00000,      2.00000 ]
	[      0.00000,      0.00000,      1.00000,      3.00000 ]
	[      0.00000,      0.00000,      0.00000,      1.00000 ]
viewport:
	[      0.00000,      0.00000,    800.00000,    600.00000 ]
=======================================================
vertex:
	[      1.50000,      1.60000,    -99.60000,      1.00000 ]
eye space:
	[      2.50000,      3.60000,    -96.60000,      1.00000 ]
clip coordinates:
	[     25.00000,    -72.49090,     94.79139,     96.60000 ]
w inverse:
	[   0.0104 ]
normalized device coordinates:
	[      0.25880,     -0.75042,      0.98128 ]
window coordinates:
	[    503.51965,     74.87299,      0.99064 ]
=======================================================
vertex:
	[      1.50000,      1.60000,      5.00000,      1.00000 ]
eye space:
	[      2.50000,      3.60000,      8.00000,      1.00000 ]
clip coordinates:
	[     25.00000,     13.09091,    -10.01802,     -8.00000 ]
w inverse:
	[  -0.1250 ]
normalized device coordinates:
	[     -3.12500,     -1.63636,      1.25225 ]
window coordinates:
	[   -850.00000,   -190.90906,      1.12613 ]
=======================================================
vertex:
	[      1.50000,      1.60000,  -1010.00000,      1.00000 ]
eye space:
	[      2.50000,      3.60000,  -1007.00000,      1.00000 ]
clip coordinates:
	[     25.00000,   -817.36353,   1007.01398,   1007.00000 ]
w inverse:
	[   0.0010 ]
normalized device coordinates:
	[      0.02483,     -0.81168,      1.00001 ]
window coordinates:
	[    409.93048,     56.49548,      1.00001 ]