.KTX File Format

Introduction

KTX 1 is the first version of the Khronos Group’s texture container, made for OpenGL and OpenGL ES. It stores a texture in exactly the form that is passed to OpenGL’s texture upload calls, so a loader can read the header, then hand each mipmap level straight to the driver. One file can hold a 1D, 2D or 3D texture, a cube map or an array, with all its mipmap levels.

Each texture is described with OpenGL’s own numbers: the type, format and internal format constants such as GL_UNSIGNED_BYTE, GL_RGBA or a compressed format such as ETC2. KTX 2 replaced it for Vulkan, but KTX 1 files are still common in OpenGL ES and Android projects.

Structure

A 12-byte identifier is followed by an endianness word and twelve 32-bit fields. Then come the key and value pairs, and then each mipmap level, largest first, each preceded by its size. The file layout page has every field.

Variants

• Khronos Texture 1 – OpenGL textures described by OpenGL constants, in either byte order
• Khronos Texture 2 – Vulkan textures with a data format descriptor and optional supercompression

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