• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Nicholas Kong

What is the significance of 0.89f?

4 posts in this topic

I was looking through some source code which said:



private static float GROUND_INERTIA = 0.89f;
private static float AIR_INERTIA = 0.89f;
And then I started having these questions:
Why 0.89 of all numbers and why is the above declared as a float instead of a double? Is it always like this? From my research, float is a 32 bit single precision number. Why not use a data type that covers more precision?
I also notice I have a project I work on, I used System.currentTimeMillis but it gives you it as data type long and the time value fluctuates between .89 and .95 when I use println to print it out.
From what I know from books: double has better precision than a long. Why not use a double? I only always use double and int when I declare variables.
Edited by warnexus

Share this post

Link to post
Share on other sites
No need to use double if you only need to represent something like 0.89.

Doubles are double the length of a float (duh), and possibly slower to operate on, so unless you need all the bits (long operations where errors can accumulate, actual need for high precision...), theres no reason to use double.

Especially since for example graphics like to use floats, people are used to them, and only switch to doubles if its needed.

Kind of like you use ints by default, instead of a 64 bit variant.

Share this post

Link to post
Share on other sites

Why 0.89 of all numbers

It's probably an arbitrary choice or something found through experimentation (empiric observation)

Why not use a data type that covers more precision?

It is true that 0.89 cannot be represented exactly by a float, and neither can a double; but it can represent it more precisely.
However the precision difference is subtle unless you're into highly accurate scientific simulations.

Once we leave the tiny difference a part, main reason is performance. 32-bit calculation are between 1.25x-4x faster depending on the device/architecture that executes them, they need half as RAM, and they waste less memory because of padding alignment (i.e. a long followed by an double requires 16 bytes instead of 12; where a long followed by a float only needs 8 bytes).

From what I know from books: double has better precision than a long. Why not use a double? I only always use double and int when I declare variables.

Double is for 64-by floating point arithmetic (an approximation of "Real" numbers from algebra) while long is a plain 32-bit integer. They're used for entirely different purpose. The 64-bit integer version is "long long" (or "__int64")

Double takes as much as ram as an __int64, and they both take twice as ram as long.
In some devices long (or even long long) is astromically faster than double (i.e. the case of Android devices that lack a floating point unit), while in other architectures there's not much difference.

You can't do bitwise logic to floating point variables (i.e. double) and if you cast back and forth to & from __int64 to do it, you'll get two LHS (load hit store) on most architectures which is a very serious performance penalty.

If you try to use double to store a 32-bit pointer, you also need to cast it, which can cause an LHS.
If you try to use double to store a 64-bit pointer, you can't, big numbers will be truncated and the program in the best case scenario will crash.

That's because __int64 can go as big as 18.446.744.073.709.551.615; while double's max integer value that can be represented is; values bigger than that start to get rounded to the closest representable even number.
long can go as big as 4.294.967.295 btw.

You may want to pass by and look at common mistakes list; and also experiment with an interactive floating point to binary converter (in java) that has educational purposes

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
Followers 0