Arcane University:Mesh Export to NIF

Meshes can be exported by the following applications:

• Blender export plugin (Version 2.69 and 2.7x)
• 3DS MAX export plugin (Versions xxx)
• CK-CMD

General NIF structure

BSShaderProperties and BSTextureSet NIF (Netimmerse Gamebryo) files in Skyrim are the files that hold the 3D Model information necessary to display objects in the game. When you open a NIF file in NifSkope, every NiTriShape represents a 3D Object instance. A single NIF file can have multiple instances of these and they can reside under various parent nodes. A NiTriShape can have the following child properties among others:

• NiTriShapeData is the actual mesh.
• BSDismemberSkinInstance is the information necessary to handle limbs being dismembered from the base mesh. Those nodes hold all skinning/rigging data. They tell the mesh how to deform during animation
• BSLightingShaderProperty holds lighting and texture information.
• NiAlphaProperty tells the game how to handle transparency in the mesh.

Nifskope Gamebryo NIF branch hierarchy example (object window): File:Branches1.PNG

Understanding BSShaderTextureSet textures and Skyrim

Textures are the only way for you to paint your mesh and make it look the way you want which means that, apart from the mesh itself, the textures will be the single most important work. As the mesh is built using triangular faces, to know what to draw on each face, you create what are known as UV Maps in Blender or 3D Studio Max. The UV Map is where you take the 3D triangles of your mesh and map them on to a flat plane. This way the game can project a texture back on to the mesh based on the information in this UV Map. It is therefore important to understand that when vertices are moved, they will stretch and shrink the face and can cause the texture to look strange. This is more an issue with how 3D engines work and not anything you can control. Just keep in mind and work around it if needed.

The shader will apply light and effects based on 2 things:

• The BSShaderTextureSet textures.
• Flags set for the BSLightingShaderProperty. Each flag only works with a specific set of textures.

Diffuse Map (Slot 1 of the Texture Set)

This texture is the base texture of the mesh and contains the main coloring your texture will use as well as the transparency information in the alpha channel. All other textures will only be detail additions and effects.

Compression:

Use DXT1 if transparency is not needed. Use DXT3 if only full transparency is needed. Use DXT5 if the texture needs partial transparency. Required properties:

For Alpha Transparency Automatically enabled for outer layer if using MultiLayer Parallax shader, otherwise requires that a NiAlphaProperty be added to the NiTriShape (right-click the NiTriShape > Node > Attach Property > NiAlphaProperty) NiTriShapeData > Has Vertex Colors NiTriShapeData > Vertex Colors Appearance Controller(s):

For Alpha Transparency NiAlphaProperty > Flags (Click the flag to view settings) BSLightingShaderProperty > Alpha 0 is fully transparent (invisible) 1 is fully visible (opaque) Transparency Map (Alpha Channel) Black is fully transparent (invisible) *dependent on NiAlphaProperty flag settings White is fully visible (opaque) *dependent on NiAlphaProperty flag settings Transparency increases as shade approaches black *dependent on NiAlphaProperty flag settings Suffix: none

The NiAlphaProperty

Click the flag icon next to flags to view the settings.

Enable Blending should be checked For Alpha Blending Source Blend Mode: Src Alpha Destination Blend Mode: Inv Src Alpha For Additive Blending Source Blend Mode: One Destination Blend Mode: One For Multiplicative Blending Source Blend Mode: Zero Destination Blend Mode: Src Color For 2x Multiplicative Blending Source Blend Mode: Dst Color Destination Blend Mode: Src Color For Alpha Testing check Enable Testing Alpha Test Function sets how transparency channel grey values (0 to 255 or black to white) will be compared to the Alpha Test Threshold value to determine what is opaque Less or Equal: Lighter will be more transparent Greater or Equal: Darker will be more transparent Alpha Test Threshold: Value from 0 to 255 (black to white) Color Blending

Color Blending Equation

(Source * SourceBlendMode) + (Destination * DestinationBlendMode)

“Source” is the color of the model materials in that pixel before blending “Destination” is the color of what is behind the model in that same pixel before blending The two values are modified by the value of the blend mode in that same pixel, then they are added together. Blend Modes (a.k.a. Blend Factor)

One: multiply by one (no modification) Zero: multiply by zero Src Color: multiply by “Source” Inv Src Color: multiply by inverse “Source” Dst Color: multiply by “Destination” Inv Dst Color: multiply by inverse “Destination” Src Alpha: multiply by value of the model’s alpha channel (diffuse and vertex colors) present at that pixel Inv Src Alpha: multiply by inverse value of the model’s alpha channel (diffuse and vertex colors)present at that pixel Dst Alpha: multiply by value of the background model’s alpha channel (diffuse and vertex colors)present at that pixel Inv Dst Alpha: multiply by inverse value of the background model’s alpha channel (diffuse and vertex colors)present at that pixel Additional information on color blending.

Normal Map (Slot 2 of the Texture Set)

The normal map, very similar to a bump map, will add the illusion of depth to the mesh. This is accomplished by creating varying shades of violet using various software including Mudbox, Zbrush, xNormal, Maya, the Gimp normal map plugin, or the Nvidia normal map plugin for Photoshop. Here is a video tutorial for creating high quality normal maps with ZBrush. The shader will then use the violet levels to determine the light levels for the texture, bending it if you wish, giving you what looks like height and depth details to the mesh.

Model Space Normal files created by Bethesda have the suffix _msn and are normal maps with no alpha channel. I prefer to use _n tangent space normal maps with the alpha channel instead of using another image and more video ram. I personally find the ability to add a specular alpha too good a thing to pass up.

It is important that NiTriShapeData > BS Num UV Sets is set to 4097 in NifSkope. If it is not, the Creation Kit, Nifskope, and the game itself will not display the Normal Map properly in game.

The Alpha Channel of the Tangent Space Normal Map

The tangent space normal map’s alpha channel will be ignored in the Skyrim game engine for transparency and instead, the intensity of the the different greyscale levels will determine how bright (specularity) that part of the mesh will be in game.

Black is minimum intensity, no specular highlight. White is maximum intensity. Intensity increases as shade approaches white. A quick and dirty way to make this brightness mask is to take your diffuse map and darken it substantially, then copy it in to the alpha channel of the normal map in Gimp or Photoshop.

Compression: Use DXT5 because of the importance of the alpha layer in this file. Bethesda uses DXT5 in all tangent space normal maps that I have observed.

Required properties:

NiTriShapeData >BS Num UV Sets = 4097 NiTriShapeData > Has Normals = yes BSLightingShaderProperty > Shader Flags 1: SLSF1_Specular Appearance Controller(s)

BSLightingShaderProperty > Specular Strength 1 is normal intensity Less than 1 is lower intensity Greater than 1 is higher intensity BSLightingShaderProperty > Specular Color The color of the specular highlight BSLightingShaderProperty > Glossiness Glossiness is the width of the specular highlight 10 is a wide specular highlight 50 is a thinner specular highlight 100 is an even thinner specular highlight Value ranges from 0 to 999 Suffix:

_n: Tangent Space Normal Map Required to use the alpha layer specular map. Tangent space normal maps are easily recognized by their mostly blue appearance. Tangent space normals almost always look bluish because normals in tangent space are always considered “up” (coordinates 0, 0, 1 ), even if in world space this is not true. The normals mapped on this triangle are thus encoded, and that’s the key point, relatively to ( 0, 0, 1 ). Because most normals are majorly “up”, and since the vector ( 0, 0, 1 ) is colorized as blue-purple-ish, the result is a blue-purple-ish normal map. The benefits of tangent space maps are the removal of the restrictions imposed by World Space and Object Space normal maps. Tangent Space normal maps can rotate and deform, therefore they are ideal for characters or objects that need to have vertex deformation, like water or tree limbs. _msn: Model Space Normal Map Does not have a specular alpha, SLSF1_Specular must be false. Slot 8 can contain a specular map if model space normals are used. Object Space normal maps can be moved, but the vertices of the mesh cannot be deformed or the shading is wrong. Object space normals are best for things that can move, but not deform, like swords, shields, doors, etc. Also note that the Creation Kit expects the normal map to be present for the mesh and will give an error message if not present.

Emissive (glow) Map (Slot 3 of the Texture Set)

This slot can either be used for an Emissive Map or for a Subsurface Color Map which is used in the MultiLayer Parallax section below.

The Emissive Map texture will add lighting to the mesh based on a few settings being set. The game will glow any color that you use / add but ignore black making this a very easy texture to apply. However, because you need to use Emissive Color for the glow base it may wash out the texture color. You may need to try different settings for this color but it will most often work fine if you use similar colors or set Emissive Color to a greyscale color.

Soft Lighting, also called wrapped diffuse adds a glow through the object to simulate light being diffused and passing through the object. Good for simulating semi-transparency on objects such as leaves.

Rim lighting is only visible when light is on the opposite side of the mesh and simulates light bending around the object and lighting it at the edges.

Compression: DXT1

Required properties:

BSLightingShaderProperty > Shader Type: Glow Shader BSLightingShaderProperty > Shader Flags 1: SLSF1_Own_Emit SLSF1_Environment_Mapping disabled BSLightingShaderProperty > Shader Flags 2:

SLSF2_Glow_Map

For Soft Lighting: SLSF2_Soft_Lighting For RIM Lighting: SLSF2_Rim_Lighting (Rim lighting overwrites soft lighting) Appearance Controller(s):

BSLightingShaderProperty > Emissive Multiple Glow intensity increases as emissive multiple increases BSLightingShaderProperty > Emissive Color Soft Lighting Specific Lighting Effect 1: Light begins in the center and higher values wrap the light further around the sides. Between 0-1 the effect also diminishes in strength such that 0.0 is completely off. Rim Lighting Specific Lighting Effect 2: Light begins on the edge and moves towards the center as the value increases. The lower the number, the more edges the light catches on. The higher the number, the sharper the effect appears. Suffix: _g

Setting up the Nif-specific shader properties and texture sets

Shader Types

1.1. Bethesda Shader Properties 1.1.1. Environment/Reflection Requirements: cube map (also called) environment map BSLightingShaderProperty => Skyrim

• Default Shader

• Environmental Shader

General Structure of a Mesh

Make sure, that you visualize it as tree diagram.

Note that there is a hierarchical order, similar to shoulder -> arm -> hand -> finger. In theory, your mesh could be sorted differently, but most meshes look like this. If you see slight variations, don’t worry too much, the system behind is the same.

The top level is most commonly a BSFadeNode (static bodies) or a Ninode (Skinned rigged meshes) or a BSLeafAnim/tree node (plants). The BSX Flag below is for activating the collision. The bhkCollision object is the mesh of the collision.

The first sublevel has the Nitrishape, which is the “body” of the mesh. There can be as many as you want.

Each Nitrishape then has a second sublevel, which contains a NirtiShape Data tab and the LightingShaderProperty. This is where we set up the way the mesh is rendered. Here, we set the shader type and the shader flags and controllers.

If you double click on the BSLightingshaderProperty, you find the third sublevel, the TextureSet, which contains your texture slots. For detailed information on DDS formate texture files, please click here. For detailed information on texture sets/texture slots of shaders, click here.

Meshes can be rendered in Skyrim according to their BSLightingShaderProperty (this article) or the BSEffectProperty (more here).

Most commonly used BSLightingShaderProperties are Default shader type (“0”) and Environment Map shader type (“1”). You set your mesh shader property type in BSLightingshaderproperties. Note that each Nitrishape can only have one shader type and a small range of optional shader flags and use specific controllers(see below).

But, if needed, you can simply use multiple Nitrishapes combined on top of each other. As an example, it might make sense to split your mesh into subsections by material (metal, leather) and export each as a different Nitrishape (first sublevel) into the same mesh. Consider a leather armor for instance. I would suggest having an organic leather/cloth part (which usually absorbs light to a high degree and would use the default shader type) and the metal elements (which would reflect light stronger and profit from cube maps used in the environment map shader type).

Available Shader Flags, Controller Settings, and Texture Slots

BSLightingShaderProperty Shader Types BSShaderFlags Controller Settings BSTextureSets They have their own unique requirements. They need specific Texture Slots to be filled, depending on their character.

Most Common Shader Types

Default (0) Shader Type Default Shader Type

use: Assets with color, height, and specularity. common examples: rocks, clothes, furniture, stones, plants, sometimes metals if specularity is done in a way that can pretend metallic reflections. necessary slots: 1) base color/diffuse map 2) normal map with specularity in alpha channel (optional) necessary flags: those who are marked green above under shader flags, for export; and additionally what you need (vertex paint, specularity for example, if you learned how to apply these)

Example picture above, and shader settings of another example below.

The textures: 1) diffuse (base color) in slot 1, and 2) normal map with optional specularity in the alpha channel in slot 2 of the BSTextureSet.

Environment Map (1) Shader Type Comment regarding Parallax shaders

Texture Types and the DTX format

• What is the DDS file format?
  • DXT is a set of compression algorithms or codecs applied to raster/bitmap images. The set is also known as S3 Texture Compression (S3TC). They all convert 4×4 blocks of pixels to either 64-bits or 128-bits depending on the codec. All are lossy algorithms. The original codecs were created by S3 Graphics, but many non-encumbered alternatives exist now. There are many different codecs: DXT1, DXT3, DXT5, etc. I’ll talk more about them in a moment. DDS (Direct Draw Surface) is an image file format, rather like a container for storing image data compressed using one of the DXT codecs. It was developed by Microsoft and introduced with DirectX 7. Together, a DDS file containing data organized using a DXT code creates an image file that can be used in most graphical applications, at least those that support DDS natively or via a plug-in. DDS files are very common in the game industry, where advantages in loading speed and video memory savings outweigh disadvantages.

• How does it work?
  • DXT sees images as collections of 4×4 blocks of pixels called “texels”. For every texel, DXT selects two colors from the texel, each determining one end of a color range of 4 colors. The middle two colors are interpolated. The sixteen pixels of the texel are then assigned a 2-bit index (0-3) that maps them to the color range. The two representative colors are stored as 16-bit RGB values (5:6:5). So each texel requires 2×16 bits for the colors, plus 16×2 bits for the indices, giving a total of 64 bits for each texel, which equates to 4 bits per pixel. So for any set of images having the same dimensions, compressed size will always be the same.

• What if the image has an alpha channel?
  • How DXT handles this depends on the codec used. In DXT5, the alpha channel is encoded using a second set of 64 bits for each texel. DXT5 stores alpha information in a way that is almost the same as color information. Two alpha values are selected and *used as the extremes for a range of transparency values. The alpha values are represented by 8 bits each, and the range indices by 3 bits each, allowing for gradients of up to 8 shades. DXT3 handles the alpha channel a little differently. Each pixel gets 4 bits to represent its alpha, for a total of 16 unique values of transparency. This allows the alpha channel to be represented more accurately than DXT5, but with less subtle transitions. So, for an image with no alpha using DXT1, compression results in an image using 4 bpp (bits per pixel). For an image using DXT3 or DXT5 incorporating an alpha channel, the requirements will be 8 bpp. Note that the actual image size will likely be larger, as it will frequently include mipmap data.

• What are the advantages of DDS files and DXT compression?
  • Fast load times. DDS files are ready to be used by the graphics system and can be read straight into graphics memory with little overhead. In situations where many files are being constantly swapped in/out of the graphics unit, this can be a substantial savings and can reduce “lag”, especially with big texture files. Mipmaps can be pre-generated and included in the DDS files. This is another savings in load times and gives the graphic designer control over mipmap construction. More on mipmaps in a moment. Data remains compressed in video memory. All image formats except DDS/DXT are loaded into graphics memory in flat, uncompressed state. (And uncompressing them takes time and resources.) DDS/DXT files remain in their compressed state in video RAM, using special algorithms on the video card to retrieve data on demand. Compression ratio is 6:1 if no alpha channel is used, or 4:1 if an alpha channel is used. This can result in huge video memory savings.

• What are the disadvantages?
  • DXT codecs are lossy. What is stored as compressed data is not the same as the original image, and on a fine level it may not even be close. Images with high contrast regions such as print or cartoon-like colors and borders will likely generate visible artifacts, particularly with smaller resolutions. For this reason DXT can be problematic when used with normal maps, though there are work-arounds. I’ll come back to this issue. Never use DDS files for editing and archiving. The compression degrades the original colors. It is not a good format where retention of the true color is critical, particularly in those situations where fine differences may have a large impact. DXT generates images using a 16 bit color depth. Where formats like JPG or PNG use 8 bits per channel per pixel (RGB 8:8:8) for a 24-bit color depth (32 bits with PNGs having an alpha channel), DXT reduces the spectrum down to 5:6:5 bits using an interpolation algorithm to arrive at the new color values. In short, you lose much of the original color range. But many graphic applications in games and sims don’t require tight control over the colors, and a good choice of the color palette can eliminate any visible results of this DXT effect. File size on disk can be large for DDS. For example, a 1024×1024 image with an alpha channel and mipmaps will result in a 1.37MB file. But file size is a relatively small consideration these days. Game/simulation performance matters far more.

• Are there any image dimension limitations?
  • DDS/DXT images can be of any dimension expressed in powers of two up to the limits of your application or hardware, but no dimension can be less than 4. So 1024×512 is fine, but 2048×2 is not. Since DXT compression works with texels and each texel is a 4×4 block of pixels, it follows that DXT can’t work with an image with a dimension smaller than 4.

• DDS and Mipmaps
  • An object seen up close needs a relatively high-resolution texture so that it doesn’t look pixelated. But an object seen in the distance needs much less resolution to look reasonable, and smaller resolutions require less resources. A mipmap is a set of pre-calculated versions of the same image progressively decreasing in size until the image reaches a dimension of 1×1. The idea is to have a handy set of smaller images that can be used to increase rendering speed and reduce aliasing effects while allowing the creator to optimize the appearance of the image at each stage. With mipmaps, the render engine can use the smaller, pre-processed version. This speeds things up significantly when you consider a scene of many objects at varying distances from the viewer. With most image file formats, the render engine must generate the mipmaps when the image is loaded. This takes time, and the render engine may not make the best choices for the appearance of the image. DDS files give you control over this process, allowing you to pre-generate mipmaps and store them ready-to-go along side the source image in the same DDS file. There is of course a penalty. Mipmaps take up space, increasing data size by 33% beyond that required to store the source image. This increases both size on disk and size in video memory. Unless your primary concern is file size, the benefits of mipmapping more than outweigh the costs.

• DXT Flavors Egad! There are tons of DXT codecs! Which should I use?
  • DXT comes in a lot of flavors. Fortunately most are specialty applications. For common situations you’ll probably need to consider only three: DXT1, DXT3 and DXT5. Let’s briefly overview each one to get an idea when they might be used.
    • DXT1 (BC1)
      • RGB, 4 bits per pixel, no alpha or 1 bit (black or white) alpha
      • DXT1 is a fixed 8:1 compression ratio

      If your image does not require an alpha channel, use the no-alpha DXT1. It uses the same compression algorithm as DXT3/5 for color data, and will get you half the file size. I’ve never used this one with an alpha channel. Sometimes referred to as BC1 (Block Compression 1).

    • DXT3 (BC2)
      • ARGB, 8 bits per pixel, explicit alpha
      • DXT3 is a fixed 4:1 compression ratio

      DXT3’s method for storing alpha is better for files that have clearly delineated defined alpha regions and values. It may result in banding artifacts if used on images with smooth blended alpha regions– use DXT5 for these cases. I rarely use DXT3.

    • DXT5 (BC3)
      • ARGB, 8 bits per pixel, interpolated alpha
      • DXT5 is same 4:1 compression ratio as DXT3

      DXT5 is the go-to codec for most images that include an alpha channel. The cost is double the file size of a DXT1 image. If you do not need an alpha channel (and I suggest that you not include an alpha channel unless you absolutely must), use DXT1.

DDS Files: editing and archiving

• DDS images are just regular images with or without an alpha channel. They can be created in GIMP or Photoshop or whatever you have. To export your image as a DDS file, you’ll need a plugin. NVIDIA offers a free tool for importing/exporting DDS files into Photoshop:

[1]

• A plugin for GIMP can be found here: [2]

Learning to use these plugins is beyond the scope of this article, but I have a few observations. It depends on the nature of the image.

• I’ve sometimes worked with images that simply refuse to export to DXT1.
• Exporting to DXT5 tends to be much faster and less problematic.
• Don’t include an alpha channel if you don’t absolutely need one. An alpha channel will double the file size of your DDS file and significantly add to game or simulation video processing workload. I commonly find images created by others that include an unnecessary, fully-transparent alpha channel. Don’t do that.
• Since DDS files are lossy and rather badly so, you should not use them as an archive format. Don’t edit DDS files if there is any possibility of using a non-lossy source, especially if the DDS file is serving as a normal map. Always begin your edits by opening a file saved in a non-lossy format. If you must edit a DDS file as your only option, first save the file in a non-lossy format, thus preserving at least that version as a standard, and create all subsequent versions from that source. If you do not, subsequent saves and editing will quickly corrupt the image into something unusable.

DXT and Normal Maps A normal map stores information that allows lighting calculations to be done at the per-pixel level rather than interpolating between vertices. This can make lighting much smoother and more graduated, or it can make significant changes how lighting affects a given point. The common use of a normal map is to tweak surface data to give the illusion of having extra detail. It’s not real detail– it doesn’t actually change the geometry, but it does change the lighting and can give very realistic results without adding polygonal complexity. Normal map data is essentially a normal vector for each pixel. The normal gives an indication of the “facing” of the pixel. Normal maps use the RGB color space to store the data needed for the effect– the 24 bits for each pixel are used to encode the pixel’s vector. Given that a color in this context is really a vector, changing a color can significantly alter the scale and direction of that vector, thus altering the effects at any given location. Since DXT compression does not exactly preserve the colors, DXT images can make a real mess of normal maps.

You can still use DXT compression for normal maps. In fact it’s common to do so in games and sims, where resolutions are fairly low and resources come at a premium. Just be aware that the end result is likely to be rather mangled. For low-res situations it’s usually not a big problem. But consider saving the normal map in a non-lossy format. You’ll lose the load-time and video RAM advantages of DDS, but you can compensate by going to a quarter-size resolution. In general for normal maps, you’ll get better appearance with a non-lossy format one-quarter the resolution of the DXT image. For example, a 512×512 PNG normal map will likely look better than a 1024×1024 DDS/DXT normal map.