• 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
Chris_F

Packing Float into RGBA Texture

6 posts in this topic

So I've looked around, and there is a lot of info to be found on this subject, but it is only for encoding floats in the range [0, 1], and I want to encode floats of arbitrary magnitude. Can you tell me if my method is sound?

 

On the CPU:

glm::ivec4 FloatToRGBA(float input)
{
    int exponent;
    float significand = frexp(input, &exponent);
    int sig_int = glm::round(significand * 16777215.0f);
    glm::vec4 output;
    output.x = exponent + 128;
    output.y = sig_int & 0x000000FF;
    output.z = (sig_int & 0x0000FF00) >> 8;
    output.w = (sig_int & 0x00FF0000) >> 16;
    return output;
}

 

On the GPU:

float RGBAtoFloat(float4 input)
{
    float significand = dot(input.yzw, float3(16711680.0f, 65280.0f, 255.0f)) / 16777215.0f;
    return ldexp(significand, input.x * 255.0f - 128.0f);
}
Edited by Chris_F
0

Share this post


Link to post
Share on other sites

Depends on what you mean by "sound." If you want to pack RGBA into a float like you would an int, there's a couple problems here. First, floats have 1 bit for sign, 8 bits for exponent, and 23 bits for the fractional part. You're not using all of the bits. You're trying to stuff 32-bits worth of information into fewer than 32 bits, so you're bound to lose some information. Second, you can potentially create an invalid float value (NaN) which, depending on your system and compiler, may result in a signaling NaN that can crash your program.

1

Share this post


Link to post
Share on other sites
Depends on what you mean by "sound." If you want to pack RGBA into a float like you would an int, there's a couple problems here. First, floats have 1 bit for sign, 8 bits for exponent, and 23 bits for the fractional part. You're not using all of the bits. You're trying to stuff 32-bits worth of information into fewer than 32 bits, so you're bound to lose some information. Second, you can potentially create an invalid float value (NaN) which, depending on your system and compiler, may result in a signaling NaN that can crash your program.

 

I think you are confused. I want to pack a float into a RGBA8, not pack an RGBA8/int into a float.

0

Share this post


Link to post
Share on other sites
I want to pack a float into a RGBA8

I'm going to assume by "RGBA8" you mean vec4 with RGBA/xyzw components in the range [0, 255], (if this isn't correct, you'll have to explain what you mean by RGBA8). FloatToRGBA is still only using 31 bits of the input, and if you want 32 bits of information in the end result, you're going to have to use all 32 bits.

 

not pack an RGBA8/int into a float.

Either way you look at it, RGBAtoFloat and FloatToRGBA are only using 31 bits of the 32 bit float. If you're okay with that, then I don't see any immediate problems (does anyone else?), but I wanted to make you aware of the fact that only 31 bits are being used.

1

Share this post


Link to post
Share on other sites

Don't you have floating-point channels available? That would be a better choice than manually packing/unpacking your IEEE float. At least I certainly know there are general-purpose floating-point texture formats in DirectX, OpenGL and OpenCL (one, two, three or four 32-bit channels, as needed) so why not glm? Or are you trying to save memory?

Edited by Bacterius
1

Share this post


Link to post
Share on other sites
I want to pack a float into a RGBA8

I'm going to assume by "RGBA8" you mean vec4 with RGBA/xyzw components in the range [0, 255], (if this isn't correct, you'll have to explain what you mean by RGBA8). FloatToRGBA is still only using 31 bits of the input, and if you want 32 bits of information in the end result, you're going to have to use all 32 bits.

 

not pack an RGBA8/int into a float.

Either way you look at it, RGBAtoFloat and FloatToRGBA are only using 31 bits of the 32 bit float. If you're okay with that, then I don't see any immediate problems (does anyone else?), but I wanted to make you aware of the fact that only 31 bits are being used.

 

 

Actually, I should probably have mentioned I don't need to suport negatives.

 

Don't you have floating-point channels available? That would be a better choice than manually packing/unpacking your IEEE float. At least I certainly know there are general-purpose floating-point texture formats in DirectX, OpenGL and OpenCL (one, two, three or four 32-bit channels, as needed) so why not glm? Or are you trying to save memory?

 

The software I'm using doesn't support FP16 or FP32 textures.

0

Share this post


Link to post
Share on other sites

If I understand you correctly, you want to take a float and encode it somehow in the 4 RGBA channels (8-bit each) and then read it back in the GPU as one float again?

If that's so, RGBE encoding could do (but you'll loose a lot of precision) or this trick could do. It may work for floats in the range [0; 1] but you can use a multiplier (divide by large number when converting to RGBA, multiply when getting the float back)

AFAIK there is no "perfect" solution that will preserve a lot of precision in this type of conversion, not at least on how GPUs work (assuming there are no integer arithmetic operations available).

1

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