View Full Version : urgent exam help pls!.what is the current matrix?

05-25-2011, 05:47 AM
in opengl i know that there is a projection matrix and a modelview matrix.but then what is the current matrix?
in the code below,glLoadIdentity() is used to load identity matrix into what matrix?why is it needed?

void display()

without the glLoadIdentity() function the object i draw gets smaller and smaller each time i minimize and maximize.

05-25-2011, 06:23 AM
The loadidentity call is similar to clearing a variable. Its is setting the current modelview matrix to identity.

Suppose you have a program which does this in the display function;

int x=0;
int dx=1;
void display(){
x+= dx; //similar to translate call

In the above code, the x variable will increment each time and then the object will move in the x direction 1 units. What we wanted was to shift the object to pos x=1; So the solution we do is this,

void display(){
x=0; //similar to loadidentity
x+= dx; //similar to translate call

NOw x will have a value of 1 and it will remain 1. I hope this helps u in understanding what is going on.

05-25-2011, 06:39 AM
Which is the "current matrix"? The first line of this will tell you the answer: http://www.opengl.org/sdk/docs/man/xhtml/glMatrixMode.xml

The last line of the "description" section also contains more useful info.

Shouldn't you already know this if you're getting to exam time?