Module glium::texture

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A texture is an image loaded in video memory, which can be sampled in your shaders.

Texture kinds

One thing that is important to understand when it comes to textures is that the way a texture is accessed (in other words, its “public API”) is disconnected from the internal representation of the data.

When it comes to accessing a texture, there are six kinds of textures:

  • Floating-point textures.
  • Integral textures (that contain signed integers).
  • Unsigned textures (that contain unsigned integers).
  • Depth textures (that contain depth information).
  • Stencil textures (that contain stencil information).
  • Depth-stencil textures (that contain at the same time depth and stencil information).

Textures have a different API depending on their kind. For example a integral texture can only be sampled in GLSL through a sampler type which is prefixed with i.

The internal format can only be chosen when the texture is created, and then can never be touched again. Integral and unsigned textures can only contain signed integers and unsigned integers.

Floating-point textures can contain either floating-points or integers. If integers are used, then the maximum value corresponds to the floating-point value 1.0 and the minimal value to 0.0. For example if a texture contains u8s and internally contains the value 128, reading from the texture will yield the value 0.5.

Dimensions

Textures come in nine different dimensions:

  • Textures with one dimension.
  • Textures with two dimensions.
  • Textures with two dimensions and multisampling enabled.
  • Textures with three dimensions.
  • Cube textures, which are arrays of six two-dimensional textures corresponding to the six faces of a cube.
  • Arrays of one-dimensional textures.
  • Arrays of two-dimensional textures.
  • Arrays of two-dimensional textures with multisampling enabled.
  • Arrays of cube textures.

The difference between a 3D texture and a 2D textures array (and between a 2D texture and a 1D textures array) is that texture arrays can only be accessed by individual layers. That is, you can only access layer 0, or layer 1, or layer 2, and so on. Whereas if you use 3D textures you can access layer 0.5 for example.

All textures except depth, stencil and depth-stencil textures have mipmaps. A mipmap is a smaller version of the texture whose purpose is to be used during rendering when the texture will be small on the screen.

Texture types in glium

In addition to the nine different dimensions types, there are nine kinds of texture formats:

  • The texture contains floating-point data, with either the Compressed prefix or no prefix at all.
  • The texture contains floating-point data in the sRGB color space, with either the Compressed prefix or not.
  • The texture contains signed integers, with the Integral prefix.
  • The texture contains unsigned integers, with the Unsigned prefix.
  • The texture contains depth information, with the Depth prefix.
  • The texture contains stencil information, with the Stencil prefix.
  • The texture contains depth and stencil information, with the DepthStencil prefix.

Each combination of dimensions and format corresponds to a sampler type in GLSL and in glium. For example, an IntegralTexture3d can only be bound to an isampler3D uniform in GLSL.

The difference between compressed textures and uncompressed textures is that you can’t do render-to-texture on the former.

The most common types of textures are CompressedSrgbTexture2d, SrgbTexture2d and Texture2d (the two dimensions being the width and height). These are what you will use most of the time.

Buffer textures

A BufferTexture is a special kind of one-dimensional texture that gets its data from a buffer. Buffer textures have very limited capabilities (you can’t draw to them for example). They are an alternative to uniform buffers and SSBOs.

See the buffer_textures module for more infos.

About sRGB

For historical reasons, the color data contained in almost all image files are not in RGB but in sRGB. sRGB colors are slightly brighter than linear RGB in order to compensate for the fact that screens darken some values that they receive.

When you load image files, you are encouraged to create sRGB textures (with SrgbTexture2d instead of Texture2d for example).

By default, glium enables the GL_FRAMEBUFFER_SRGB trigger, which expects the output of your fragment shader to be in linear RGB and then turns it into sRGB before writing in the framebuffer. Sampling from an sRGB texture will convert the texture colors from sRGB to RGB. If you create a regular RGB texture and put sRGB data in it, then the result will be too bright.

Bindless textures

Bindless textures are a very recent feature that is supported only by recent hardware and drivers.

Without bindless textures, using a texture in a shader requires binding the texture to a specific bind point before drawing. This not only slows down rendering, but may also prevent you from grouping multiple draw calls into one because of the limitation to the number of available texture units.

Instead, bindless textures allow you to manually manipulate pointers to textures in video memory. You can use thousands of textures if you want.

Re-exports

Modules

Structs

  • RawImage1d
    Represents raw data for a two-dimensional image.
  • RawImage2d
    Represents raw data for a two-dimensional image.
  • RawImage3d
    Represents raw data for a two-dimensional image.
  • TextureAny
    A texture whose type isn’t fixed at compile-time.
  • TextureAnyImage
    Represents a specific 2D image of a texture. 1D textures are considered as having a height of 1.
  • TextureAnyLayer
    Represents a specific layer of an array texture and 3D textures.
  • TextureAnyLayerMipmap
    Represents a specific layer of a specific mipmap. This is the same as TextureAnyImage, except for 3D textures, cubemaps and cubemap arrays.
  • TextureAnyMipmap
    Represents a specific mipmap of a texture.

Enums

Traits

Functions