Texture types and their usage

Texture types and their usage

Overview

At the moment FUSEE supports two types of textures. Standard textures, that offer access to the pixel data and Writable Textures, that don't.
The latter are used if we want to render to a texture or a G-Buffer, standard textures are used e. g. in ShaderEffects as albedo or normal texture.

The following class diagram breaks down the implementation:

Textures, WritableTextures and WritableCubeMaps are meant to be used directly in application code. Furthermore the associated interfaces ITexture, IWritableTexture and IWritableCubeMap -- here marked in green -- serve as their abstraction and allow us to use the texture classes in a cross-platform context.

Textures

Loading

Images can be loaded via the AssetStorage:

var imgData = AssetStorage.Get<ImageData>("someTexture.png");
var tex = new Texture(imgData);

The first line creates a object of type ImageData, which carries the payload of the image (the pixel data) and offers Blt functionality, which is also inherited by the standard Texture. The second wraps it into a texture object.

Currently the engine supports the following image formats to be loaded by the AssetStorage:

• jpg
• jpeg
• png
• bmp

Writable Textures

They are not meant to be manipulated directly by the user, but can serve as render target, e. g. in multipass rendering. Therefore we do not have access to the actual pixel data here. To create a WritableTexture the class offers a handful of static methods for special types, that make sure the texture is created correctly on the gpu. The types reflect the ones used in the deferred rendering pipeline:

• Albedo
• Position
• Normal
• Specular
• SSAO
• Depth

If we want to use a WritableTexture in an arbitrary case, CreateAlbedoTex may be the safest choice. Alternatively we can call the constructor directly, but we have to pass a set of texture options (see Texture Options)

Using textures in ShaderEffects

To feed a texture to a ShaderEffect and use it as a uniform variable in the associated shader code, we can pass it a FxParamDeclaration to the constructor of the ShaderEffect:

var effectParams = new IFxParamDeclaration[]
{
    new FxParamDeclaration<Texture>
    {
        Name = UniformNameDeclarations.AlbedoTexture,
        Value = tex
    },

    [...]
}

var effect = new ShaderEffect(fxPassDeclaration, effectParams);

Make sure to set the name of the FxParamDeclaration to the name of the uniform variable.

Texture Options

The options of a texture define how it is created and handled on the gpu. The engine offers the following:

Type	Name	Function
enum	ImagePixelFormat	Defines the color format, e. g. RGB, RGBA or Depth and, from this, the bytes per pixel.
bool	DoGenerateMipMaps	Defines whether mip maps are created on the gpu or not.
enum	TextureWrapMode	Describes how the texture should be sampled when a uv coordinate is outside the range of 0 to 1.
enum	TextureFilterMode	Describes which texel to map the texture coordinate to. This is important, because the texture coordinates are resolution independent and described as floating point values.