Wayland-drm pixel formats

This page describes the formats used by the private wl_drm extension, implemented by Mesa. This extension has been superseded by the linux-dmabuf extension, which provides a generic buffer-exchange protocol using the DRM pixel format descriptors.

The wayland-drm pixel formats follow the scheme:

WL_DRM_FORMAT_{component-format}

The component-format part specifies the order and sizes of the components. All the components are listed first, optionally followed by their corresponding sizes in bits (e.g., RGB888, YUVY).

The wayland-drm formats are a subset of the drm fourcc formats.

There are a few categories of wayland-drm formats:

RGBA formats: WL_DRM_FORMAT_{rgba-componenent-format}

The rgba-component-format specifies the order and sizes of the components in a native type on a little-endian system, with the leftmost component stored in the most significant bits, and the rightmost in the least significant bits.

Although the formats are expressed in terms of a native type, the addition of little-endianness specification makes the format endianness-independent.

For formats where components occupy whole bytes, an alternative, and probably more straightforward way to express the expected order, is that the component-list specifies the order of the components in memory with the leftmost component at the highest address and the rightmost at the lowest addres.

Example: WL_DRM_FORMAT_ARGB8888

Always stored as B, G, R, A in memory (B at lowest address, A at highest)

Example: WL_DRM_FORMAT_RGB565

Always stored in memory as:
```
  0                1
  M              L M              L
  G₂G₁G₀B₄B₃B₂B₁B₀ R₄R₃R₂R₁R₀G₅G₄G₃
```
Packed Y’CbCr: WL_DRM_FORMAT_{yuva-componenent-format}

The yuva-component-format specifies the order of the components in a 32-bit native type on a little-endian system, with the leftmost component stored in the least significant bits, and the rightmost in the most significant bits. In this format category each components is always 8 bits long.

An alternative, and probably more straightforward way to interpret the yuva-component-format, is that it specifies the order of the components in memory with the leftmost component at the lowest address and the rightmost at the highest.

Example: WL_DRM_FORMAT_YUYV

Always stored as Y₀, U, Y₁, V in memory (Y₀ at lowest address, V at the highest)
Multi-plane formats:

We won’t describe these in detail in this guide.