| 1 0 0 0 |
| 0 1 0 0 |
| 0 0 0 1/focus |
| 0 0 -1 0 |
M_P
| 1 0 0 0 |
| 0 1 0 0 |
| 0 0 0 1/focus |
| 0 0 -1 0 |
v
| x |
| y |
| z |
| 1 |
| x |
| y |
| -1 |
| z/focus |
// shouldn't it be :
| x |
| y |
| 1/focus |
| -z |
// ?
Perspective Matrix Mistake?
Author
Hello,
I think I've spotted a unreported mistake in the book, "OpenGL Game Programming". On page 82 where Perspective Matrix
are described. The author defines the OpenGL perspective matrix as :
The author then multiplies the perspective matrix by a vector point :
And gets this as the product :
~Khaosifix
Is this example in matrix algebra or C code? If it's in C code then this is correct, since OpenGL uses column-major matrices, not row-major matrices, so the matrix defined by:
is actually the matrix:
1 0 0 0
0 1 0 0
0 0 0 -1
0 0 1/focus 0
Enigma
float mat4[16] = { 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1/focus, 0, 0, -1, 0}is actually the matrix:
1 0 0 0
0 1 0 0
0 0 0 -1
0 0 1/focus 0
Enigma
Author
Aw man. Thanks. Looking at it from a matrix algebra perspective its wrong but I didn't know about the column major thingy OpenGL does.
Why does OpenGL do that? It makes it more confusing IMO.
Why does OpenGL do that? It makes it more confusing IMO.
I think they did it to optimize their vertex pipeline, the way they store it they can read the whole matrix continiously instead of hopping back and forth between the rows which costs some extra time. Not really sure though but that seems reasonable.
>>Why does OpenGL do that? It makes it more confusing<<
theres been a few explanations over the years perhaps google will help
theres been a few explanations over the years perhaps google will help
Author
Quote:
By Enigma
Is this example in matrix algebra or C code? If it's in C code then this is correct, since OpenGL uses column-major matrices, not row-major matrices, so the matrix defined by:
float mat4[16] = {
1, 0, 0, 0,
0, 1, 0, 0,
0, 0, 0, 1/focus,
0, 0, -1, 0
}
is actually the matrix:
1 0 0 0
0 1 0 0
0 0 0 -1
0 0 1/focus 0
Enigma
http://www.opengl.org/resources/faq/technical/transformations.htm#tran0005
The link speaks for itself.
This topic is closed to new replies.
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