Comments on: Running OpenGL3.0 – part3

By: Daniel

Daniel — Sat, 12 Feb 2011 04:24:29 +0000

I used these at first to learn and get some basic design down for my renderer, but I moved to GLM… and my god is it much *much* faster. I’d say for most, GLM is the better alternative if your not looking to roll your own.

By: Peter Wallström

Peter Wallström — Wed, 05 Jan 2011 13:49:56 +0000

no, well it could work that way (and in some game engines with a strongly hierarchal object tree structure its the preferred way), but openGL before 3.0 sure didn’t, it does things the way i have done here, just “under the hood”.

By: Kryten

Kryten — Tue, 28 Dec 2010 15:31:04 +0000

Hm ok, maybe I didn’t understand correctly what these functions do. I thought OpenGL was some how managing a stack of matrices and these were for adding a new (identity) one to apply specific transformation (that how I use them in my current code).

What I started to code is an implementation of what I described above with final coordinates computed by multiplying all matrices in the stack and finally multiplying with the vertex coordinate.

Is it correct ?

Alexandre

By: Peter Wallström

Peter Wallström — Mon, 27 Dec 2010 21:14:42 +0000

glPushMatrix and glPopMatrix is mostly just used either to switch between orthographic and perspective rendering or deal with nested transformations/rotations, in both cases we can actually just temporarily save the matrix in question in an float[16] or make the matrix as a part of the object structure.
if you really like you could create your own versions of these functions but it’s probably harder than just copying an array with memcpy(MatrixA,MatrixB,64);

I guess the absolutely best way would be to make a really object class that whenever you select an object for rendering it automatically creates the right matrix and makes sure it’s used.

By: Kryten

Kryten — Mon, 27 Dec 2010 17:04:40 +0000

Hi,

I was just wondering, starting from your code, what would be the best practice to deal with glPushMatrix and glPopMatrix?

Thanks,

Kryten

By: Peter Wallström

Peter Wallström — Tue, 13 Jul 2010 16:55:42 +0000

for a few simple reasons.
1. these tutorials assume that you already know some of this, either trough nehe or other places.
2. it’s written to be as general as possible as i don’t know what kind of codebase or language any one person is running, especially for the last 5 (VAO to Screenshots)
3. for the ones that are missing code i actually don’t have any specific source code, it’s all integrated into other code which i cant release without cleaning it up

Though the next few might be better on the sourcecode area, at least the final one in a series i am planning.

By: amir

amir — Tue, 13 Jul 2010 16:26:03 +0000

Hey your guides are awesome but one thing is missing and that is the source code i just wonder why you dont publish that ?

By: Peter Wallström

Peter Wallström — Tue, 04 May 2010 15:07:44 +0000

-old comments-

Comment by Overlord on 2009:10:03 17:37
have a gldOrtho here also by popular request

void gldOrtho(float *m, float left, float right, float bottom, float top, float Znear, float Zfar)
{

float m2[16] = {0};

m2[0] = 2/(right-left);
m2[1] = 0;
m2[2] = 0;
m2[3] = -((right+left)/(right-left));

m2[4] = 0;
m2[5] = 2/(top-bottom);
m2[6] = 0;
m2[7] = -((top+bottom)/(top-bottom));

m2[8] = 0;
m2[9] = 0;
m2[10] = 2/(Zfar-Znear);
m2[11] = -((Zfar+Znear)/(Zfar-Znear));

m2[12] = 0;
m2[13] = 0;
m2[14] = 0;
m2[15] = 1;

gldMultMatrix(m,m2);

}

Comment by Øystein on 2009:10:28 18:07
What do you do if you have two objects thath you want to translate/rotate separately? You have only one model/view/projection-matrix, projMat, for the whole scene, right?

Comment by Overlord on 2009:10:29 07:54
no, you make one matrix per object if needed, you upload matrix 1 then draw object 1, then upload matrix 2 then draw object 2 and so on.
Though it would be good to reuse certain base matrices.