Do Use Mipmapping

This increases texture cache efficiency, which reduces bandwidth and increases performance.

This increases texture cache efficiency, which reduces bandwidth and increases performance.

Mipmaps are smaller, pre-filtered variants of a texture image, representing different levels of detail of a texture. By using a minification filter mode that uses mipmaps, the graphics core can be set up to automatically calculate which level of detail comes closest to mapping the texels of a mipmap to pixels in the render target. This means it can then use the right mipmap for texturing.

Using mipmaps has two important advantages:

  1. It increases graphics rendering performance by massively improving texture cache efficiency, especially in cases of strong minification - the texture data is more likely to fit inside tile memory.
  2. It improves image quality by reducing aliasing that is caused by the under sampling of textures that do not use mipmapping.

The single limitation of mipmapping is that it requires approximately a third more texture memory per image. Depending on the situation, this cost may be minor when compared to the benefits in terms of rendering speed and image quality.

There are some exceptions where mipmaps should be avoided. For example:

  • Where filtering cannot be applied sensibly, such as for textures that contain non-image data such as indices or depth textures.
  • Textures that are never minified, such as UI elements where texels are always mapped one-to-one to pixels.

Ideally mipmaps should be created offline using a tool like PVRTexTool, which is available as part of the PowerVR Graphics Tools and SDK.

It is possible to generate mipmaps at runtime, which can be useful for updating the mipmaps for a render to texture target. In OpenGL ES this can be achieved using the function glGenerateMipmap. In Vulkan there is no such built in function, and developers must generate mipmaps manually.

Generation of mipmaps online will not work with compressed textures such as PVRTC, which must have their mipmaps generated offline. A decision must be made as to which cost is the most appropriate: the storage cost of offline generation, or the runtime cost (and increased code complexity in the case of Vulkan) of generating mipmaps at runtime.