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get projection matrix

Started by lamtab May 30, 2009 at 9:16 AM 7 replies 5.2k views

Original Post

May 30, 2009 at 9:16 AM

Hello all!!!! I'd like some help getting the projection matrix. I use the following code but it doesnt seem to work properly. What id does is get the same matrix no matter what transformations I apply. glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(80,1.0,1.0,5000.0); glTranslatef(100.0,-10.0,-5.0f); //Here I render the geometry. no transformations are taking place. glGetFloatv(GL_PROJECTION_MATRIX, projectionMatrix); projectionMatrix is an array float[16] No matter any changes to the translatef parameters the projectionMatrix is always the same. Thanks in advance...

Pooya65

May 30, 2009 at 10:58 AM

switch to modelview matrix then use glTranslatef

glMatrixMode (GL_MODELVIEW);
glLoadIdenity();
glTranslatef(x,y,z);
// render jeomtry

calling projection matrix at first of program is enought and you dont need to recalculate and load it in every frame.

lamtab

May 30, 2009 at 11:09 AM

I've tried that and the projection matrix is still the same.
What i'm actually trying to do is get the projection matrix before and after the translate command.

Pooya65

May 30, 2009 at 11:25 AM

are u check it in every frame?

i think becase you are using glLoadIdentity , its values is same in every frame.

lamtab

May 30, 2009 at 11:43 AM

yeap in every frame i print the matrices.
u mean i shouldnt use loadidentity?

can u give me a small example of how u think this should be done?
(i mean with code)
something like

glGetFloatv(GL_PROJECTION_MATRIX, projectionMatrixA);
gluPerspective(80,1.0,1.0,5000.0);
glTranslatef(100.0,-10.0,-5.0f);
//geomtry
glGetFloatv(GL_PROJECTION_MATRIX, projectionMatrixB);

RabidDog

May 30, 2009 at 12:03 PM

Curious as to why you want to translate the projection matrix. The view matrix is ideally for the camera, the world matrix for your objects.

lamtab

May 30, 2009 at 12:03 PM

i need the projection matrices to apply motion blur :)

Pooya65

May 30, 2009 at 12:25 PM

void init_func()
{
// load projection matrix
}

void render_func()
{
glMatrixMode(GL_PROJECTION);
glTranslatef (x,y,z);
// render some thing
glMatrixMode(GL_MODELVIEW);
glLoadIdentity()
// render object
...

}

lamtab

May 30, 2009 at 12:35 PM

thx pooya65.
i had in mind something like this myself. i was just missing something.

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