Re: Structs versus Vectors

• Subject: Re: Structs versus Vectors
• From: "Richard S. Wright Jr." <email@hidden>
• Date: Thu, 8 May 2008 16:41:03 -0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Richard

On May 8, 2008, at 4:33 PM, John Stiles wrote:

I'm surprised that no one has yet said "avoid immediate mode."
Immediate mode is not really recommended for real development; it's slow and doesn't really match the design of the hardware any more.
You should really use glDrawElements or something like that. That's more important than whether you use a struct array or a float array (since the compiler will generate basically the same code either way).

Jocelyn Houle wrote:

You can always do:

NSPoint p;
glVertex2fv((float *)&p);

Careful, NSPoint is a typedef of CGPoint in 64-bit (and optionally in
32-bit) with the 10.5 SDK, and CGFloat is a double in 64-bit.

Indeed...  I assumed too much...

So, let's come back to Richard's original question, which was:
---
So I am thinking that the OpenGL vector data type and corresponding function looks extremely loop friendly. Maybe I should pattern my geometric primitives and associated functions after OpenGL not Cocoa. I have not gotten into Core Data yet so I am not sure which data type would be more compatible a struct or a vector (array).

Any comments or suggestions on structs versus vectors?
---

I usually write a small class (or struct, same difference) such as:
 struct MyPoint
 {
   float x;
   float y;
 };

To loop by index, I redefine the operator[] in C++ and/or write a small ptr() method return the address of the first member.

And if you want to go crazy, you can go with unions:
 struct MyPoint
 {
   union
   {
     struct
     {
       float x;
       float y;
     };
     float ptr;
   }
 };
where you can access things like:
 MyPoint pt;
 pt.x = 1.0f;
 pt.ptr[1] = 2.0f;

Of course, I've got full-fledge interface beyond that, but it gives an idea.

So, in the end, I've got BOTH struct and vector forms... Best of both worlds. ;-)

Enjoy!
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