PDA

View Full Version : Quick question: Newbie and modelview-matrix..

newsb
05-01-2012, 11:02 AM
Consider this pseudo-code (partly from python, you'll get the idea, I think):

A44 = matrix([\
[ 0.96126169, 0., 0.27563736, 0],\
[ 0.07597595, 0.96126169, -0.26495963, 0],\
[ -0.26495963, 0.27563736, 0.92402405, 0],\
[ 0, 0, 0, 1])

glMultMatrixf(Anew)
// Drawing some stuff works ok
model = glGetDoublev(GL_MODELVIEW_MATRIX)
print "model = \n", model

// This prints the following out to screen:
//model =
//[[ 1. 0. 0. 0.]
// [ 0. 1. 0. 0.]
// [ 0. 0. 1. 0.]
// [ 0. 0. 0. 1.]]
// But why is it still identity matrix, like it's unaffected by multiplication???

And then I have another problem:

A44 = matrix([\
[ 0.96126169, 0., 0.27563736, 0],\
[ 0.07597595, 0.96126169, -0.26495963, 0],\
[ -0.26495963, 0.27563736, 0.92402405, 0],\
[ 0, 0, 0, 1])
// Trying to draw some new things - don't work - nothing happens!

// And once again, when I try to print out current modelview matrix, I get 4x4 identity - why???

In the last case, I suspect that the A44 matrix I've given isn't precise enough and then I suspect that the matrix isn't orthogonal - hence nothing is drawn. Is that guess correct (that I need more digits to A44) ???

carsten neumann
05-01-2012, 11:25 AM
You set values on A44, but pass Anew to the OpenGL functions.
Also, are you sure GL_MODELVIEW is the current matrix mode (set with glMatrixMode())?

newsb
05-01-2012, 12:03 PM
You set values on A44, but pass Anew to the OpenGL functions.
Also, are you sure GL_MODELVIEW is the current matrix mode (set with glMatrixMode())?

Oh, damn... I'm sorry, I was too fast because actually A44 = Anew. Besides that, I just inserted " glMatrixMode(GL_MODELVIEW) " just before

My guess is that it will fail for sure, if I for instance define A44 with only 1 digit after the comma (because then the matrix is not orthogonal and I guess then it'll not show anything?) ? Is this assumption correct? Maybe I should post some python code for you, however my impression is that most people here use C++... I hoped what I had already posted would suffice, however it's good to know that you also feel this should work (so I know I'm not alone)... Maybe I made a stupid mistake somewhere. I hope more people will tell their opion... Thanks a lot for your suggesion, though I don't think my problem is yet solved.

BionicBytes
05-02-2012, 03:00 AM
model = glGetDoublev(GL_MODELVIEW_MATRIX)

Firstly, what are you using doubles instead of floats?
Secondly, glGetFloatv and freinds take two arguments not one. The first is the enumerant, the second is a pointer.

procedure TMatrix44.GetModelViewMatrix(var result: TMatrix44);
begin
glGetFloatv(GL_MODELVIEW_MATRIX, @result.M.glmatrixf[0]);
end;

newsb
05-06-2012, 03:04 PM
Thanks a lot for a good answer. I gave up and thought nobody could help - still, my problem is unsolved.
About why using doubles vs. floats: Not 100% sure, but here it says that double is better than float:

http://3dengine.org/Avoid_glGetFloat_in_Python

I'm using python, so my syntax should be ok, at least that's what I think. So in python, I guess there's only one argument and then a matrix that is returned/popped back from the stack...

newsb
05-06-2012, 04:34 PM
hmm. Maybe it's my own mistake. Explaining a bit better, what I do (very simplified, removed a lot for simplicity):

glutDisplayFunc(display)

def display():
global lightZeroPosition
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
gluLookAt(0,0,10,0,0,0,0,1,0)
glCallList(1) # <<=========== display list, look into here...

# light stuff
glutSwapBuffers()
return

Display list number 1:

def setupDispList():
# setup display list
glNewList(1,GL_COMPILE)
glPushMatrix()
drawSomething() # <<<===== look into this function...
gluCylinder(cyl, 0.3, 0.3, 0.5, 12, 12)
glPopMatrix()
glEndList()

def drawSomething():
glPushMatrix()

# here I do my glLoadmatrixf (doesn't work) and/or glMultMatrixf(works)
A44 = matrix([\
[ 0.96126169, 0., 0.27563736, 0],\
[ 0.07597595, 0.96126169, -0.26495963, 0],\
[ -0.26495963, 0.27563736, 0.92402405, 0],\
[ 0, 0, 0, 1])

if 1: