Jump to content

Compressed Vertex Arrays

Josh

122 views

My work with the MD3 format and its funny short vertex positions made me think about vertex array sizes. (Interestingly, the Quake 2 MD2 format uses a single char for vertex positions!)

Smaller vertex formats run faster, so it made sense to look into this. Here was our vertex format before, weighing in at 72 bytes:

struct Vertex
{
	Vec3 position;
	float displacement;
	Vec3 normal;
	Vec2 texcoords[2];
	Vec4 tangent;
	unsigned char color[4];
	unsigned char boneweights[4];
	unsigned char boneindices[4];
}

According to the OpenGL wiki, it is okay to replace the normals with a signed char. And if this works for normals, it will also work for tangents, since they are just another vector.

I also implemented half floats for the texture coordinates.

Here is the vertex structure now at a mere 40 bytes, about half the size:

struct Vertex
{
	Vec3 position;
	signed char normal[3];
	signed char displacement;
	unsigned short texcoords[4];
	signed char tangent[4];
	unsigned char color[4];
	unsigned char boneweights[4];
	unsigned char boneindices[4];
}

Everything works with no visible loss of quality. Half-floats for the position would reduce the size by an additional 6 bytes, but would likely incur two bytes of padding since it would no longer by aligned to four bytes, like most GPUs prefer. So it would really only save four bytes, which is not worth it for half the precision.

Another interesting thing I might work into the GMF format is Draco mesh compression by Google. This is only for shrinking file sizes, and does not lead to any increased performance. The bulk of your game data is going to be in texture files, so this isn't too important but might be a nice extra.

  • Like 2


2 Comments


Recommended Comments

In fact, Leadwerks model files are usually measured in kilobytes rather than megabytes, so compressing those further would make very little difference in your game data size.

Share this comment


Link to comment

My best guess is this yielded a 7% performance boost, across the board. I'm not going to test in detail because it takes a lot of changes to modify the vertex format.

Share this comment


Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Add a comment...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Blog Entries

    • By jen in jen's Blog 3
      I thought I would share my experience on this; if you're working on Multiplayer, you will need to protect your packets. The solution is simple, let's go through how we can achieve this by implementing what Valve calls "challenge codes". (Some reading on the topic from Valve here: https://developer.valvesoftware.com/wiki/Master_Server_Query_Protocol#Challenge_response).
      Disclaimer: this doesn't cover other security techniques like authoritative server or encryption.
      So, I've worked on Border Recon last year (I think) and I needed a way to protect my server/client packets. There was no need for me to re-invent the wheel, I just had to copy what Valve has had for a  long time - challenge  codes.
      The idea behind challenge codes is similar to Captcha, but not exactly. Think of it like this: for every packet submitted to the server, it must be verified - how? By requiring the client to solve challenges our server provides.
      To implement this we need to have the following:
      A randomised formula in the server i.e.: a = b * c / d + e or a = b / c + d - e, be creative - it can be any combination of basic arithmetic or some fancy logic you like and can be however long as you want - do consider that the longer the formula, the more work your server has to do to make the computation.  Copy the same formula to the client. A random number generator.  So the idea here is:
      (Server) Generate a random number (see 3 above) of which the result would become the challenge code, (Server) run it through our formula and record the result. (Client) And then, we hand over the challenge code to the client to solve (an authentic client would have the same formula implemented in its program as we have on the server). For every packet received from the player, a new challenge code is created (and the player is notified of this change by the server in response). For every other packet, a new challenge code is created. (Client) Every packet sent to the server by the client must have a challenge code and its answer embedded.  (Server receives the packet) Run the challenge code again to our formula and compare the result to the answer embedded on the client's packet. (Server) If the answers are different, reject the packet, no changes to the player's state. The advantage(s) of this strategy in terms of achieving the protection we need to secure our server:
      - For every packet sent, new challenge code is created. Typically, game clients (especially FPS) will update its state in a matter of ms so even if a cheater is successful at sniffing the answer to a challenge code it would be invalidated almost instantaneously. 
      - Lightweight solution. No encryption needed. 
      Disadvantage(s):
      - The formula to answering the challenge code is embedded to the client, a cheater can de-compile the client and uncover the formula. Luckily, we have other anti-cheat solutions for that; you can implement another anti-cheat solution i.e. checking file checksums to verify the integrity of your game files and more (there are third-party anti cheat solutions out there that you can use to protect your game files).
       
       
       
    • By Josh in Josh's Dev Blog 4
      New commands in Turbo Engine will add better support for multiple monitors. The new Display class lets you iterate through all your monitors:
      for (int n = 0; n < CountDisplays(); ++n) { auto display = GetDisplay(n); Print(display->GetPosition()); //monitor XY coordinates Print(display->GetSize()); //monitor size Print(display->GetScale()); //DPI scaling } The CreateWindow() function now takes a parameter for the monitor to create the window on / relative to.
      auto display = GetDisplay(0); Vec2 scale = display->GetScale(); auto window = CreateWindow(display, "My Game", 0, 0, 1280.0 * scale.x, 720.0 * scale.y, WINDOW_TITLEBAR | WINDOW_RESIZABLE); The WINDOW_CENTER style can be used to center the window on one display.
      You can use GetDisplay(DISPLAY_PRIMARY) to retrieve the main display. This will be the same as GetDisplay(0) on systems with only one monitor.
    • By Josh in Josh's Dev Blog 1
      A huge update is available for Turbo Engine Beta.
      Hardware tessellation adds geometric detail to your models and smooths out sharp corners. The new terrain system is live, with fast performance, displacement, and support for up to 255 material layers. Plugins are now working, with sample code for loading MD3 models and VTF textures. Shader families eliminate the need to specify a lot of different shaders in a material file. Support for multiple monitors and better control of DPI scaling. Notes:
      Terrain currently has cracks between LOD stages, as I have not yet decided how I want to handle this. Tessellation has some "shimmering" effects at some resolutions. Terrain may display a wire grid on parts. Directional lights are supported but cast no shadows. Tested in Nvidia and AMD, did not test on Intel. Subscribers can get the latest beta in the private forum here.

       
       
×
×
  • Create New...