Displaying and transforming objects in layers

OpenGL OpenGL: Basic Coding
1

Using the glDisplayfunc();, I want to display and transform individual objects in layers but its misbehaving instead. I know about how open gl executes the matrices at the bottom of the function first during any translations.

However aside from that I don’t know how I can apply individual transformations in layers.

//basically when I add the static_object, the transformations for background are tampered with. Any help here?

void Display()
{
	 Background();
	 Static_object();
	glutSwapBuffers();
	Sleep(15);//delay (frame change)
}
2

Any help here?

How can we help if you don’t show what you’re doing? The problem isn’t with these 4 lines of code; the problem is within the functions that these lines of code call.

3

Perhaps what you’re looking for is glPushMatrix/glPopMatrix. These allow you to isolate transformations that apply only to an single object from tranforms that apply to the whole layer.

e.g.


// generic transforms for world setup
glPushMatrix()  // save pre-layer1 transforms
  // transform the layer1 (e.g. translation for all objects in layer 1)
  glPushMatrix()  // save pre-object A
    // transform object A in layer 1 (e.g. rotation this object only)
    // draw object A
  glPopMatrix() // back to layer 1 transforms
  glPushMatrix() 
    // transform object B within layer 1
  glPopMatrix() // back to layer 1
glPopMatrix() // back to world
glPushMatrix() // save world
  // transforms common to all layer 2 objects
  glPushMatrix() 
    // transform object C within layer 2
    // draw object C
  glPopMatrix() // back to layer 2
glPopMatrix() // back to world

If you don’t have the glPushMatrix/glPopMatrix functions in the version of OpenGL you are targeting, you will have to manage this yourself.

NOTE: The “layers” above are purely conceptual. In reality you are always drawing objects – you don’t actually “draw layers”. But you can apply common transformations to all objects that you consider to be in the same layer.