Roughly speaking, a color profile describes the color space of content
or an output. Under the hood, the description includes one or more ways
to map colors between the profile space and some standard profile
connecting space (PCS).
This object is not called a color space. A color space has a unique
definition, while a color profile may contain multiple different
mappings depending on render intent. Some of these mappings may be
subjective, with an artistic touch.
When a source color profile and a destination color profile are combined
under a specific render intent, they produce a color transformation.
Color transformations are already preresented by weston_color_transform.
This patch adds the basic API for color profile objects. Everything
worthwhile of these objects is implemented in the color managers:
color-noop never creates these, and in color-lcms they are basically a
container for cmsHPROFILE, the Little CMS object for color profiles.
Color profile objects will not be interpreted outside of the color
managers, unlike color transformations.
For a start, the color manager API has one function to create color
profiles: from ICC profile data. More creation functions for other
sources will be added later.
The API has errmsg return parameter for error messages. These are not
simply weston_log()'d, because CM&HDR protocol will allow clients to
trigger errors and the protocol handles that gracefully. Therefore
instead of flooding the compositor logs, the error messages will
probably need to be relayed back to clients.
Color-lcms is expected to create a cmsHPROFILE for all kinds of color
profiles, not just for those created from ICC profile data. Hence,
color-lcms will fingerprint color profiles by the MD5 hash which Little
CMS computes for us. The fingerprint is used for de-duplication: instead
of creating copies, reference existing color profiles.
This code is very much based on Sebastian Wick's earlier work on Weston
color management, but structured and named differently.
Co-authored-by: Sebastian Wick <sebastian@sebastianwick.net>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This is needed when the compositor produces any content internally:
- the lines in triangle fan debug
- the censoring color fill (unmet HDCP requirements)
Solid color surfaces do not need this special-casing because
weston_surface is supposed to carry color space information, which will
get used in gl_shader_config_init_for_view().
This makes sure the internally produced graphics fit in, e.g on a
monitor in HDR mode.
For now, just ensure there is an identity transformation. Actual
implementations in GL-renderer will follow later.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This is needed when drawing anything internal directly to an output,
like the borders/decorations in a nested compositor setup. This makes
the assumption that the internal stuff starts in sRGB, which should be
safe. As borders are never blended with other content, this should also
be sufficient.
This patch is a reminder that that path exists, rather than a real
implementation. To be implemented when someone needs it.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This is the blending space to monitor space color transform. It needs to
be implemented in the renderers, unless a backend sets
from_blend_to_output_by_backend = true, in which case the backend does
it and the renderer does not.
The intention is that from_blend_to_output_by_backend can be toggled
frame by frame to allow backends to react to dynamic change of output
color profile.
For now, renderers just assert that they don't need to do anything for
output color transform.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
See: https://gitlab.freedesktop.org/wayland/weston/-/issues/467#note_814985
This starts building the framework required for implementing color
management.
The main new interface is struct weston_color_manager. This commit also
adds a no-op color manager implementation, which is used if no other
color manager is loaded. This no-op color manager simply provides
identity color transforms for everything, so that Weston keeps running
exactly like before.
weston_color_manager interface is incomplete and will be extended later.
Colorspace objects are not introduced in this commit. However, when
client content colorspace and output colorspace definitions are
combined, they will produce color transformations from client content to
output blending space and from output blending space to output space.
This commit introduces a placeholder struct for color transforms,
weston_color_transform. Objects of this type are expected to be heavy to
create and store, which is why they are designed to be shared as much as
possible, ideally making their instances unique. As color transform
description is intended to be generic in libweston core, renderers and
backends are expected to derive their own state for each transform
object as necessary. Creating and storing the derived state maybe be
expensive as well, more the reason to re-use these objects as much as
possible. E.g. GL-renderer might upload a 3D LUT into a texture and keep
the texture around. DRM-backend might create a KMS blob for a LUT and
keep that around.
As a color transform depends on both the surface and the output, a
transform object may need to be created for each unique pair of them.
Therefore color transforms are referenced from weston_paint_node. As
paint nodes exist for not just surface+output but surface+view+output
triplets, the code ensures that all paint nodes (having different view)
for the same surface+output have the same color transform state.
As a special case, if weston_color_transform is NULL, it means identity
transform. This short-circuits some checks and memory allocations, but
it does mean we use a separate member on weston_paint_node to know if
the color transform has been initialized or not.
Color transformations are pre-created at the weston_output
paint_node_z_order_list creation step. Currently the z order lists
contain all views globally, which means we populate color transforms we
may never need, e.g. a view is never shown on a particular output.
This problem should get fixed naturally when z order lists are
constructed "pruned" in the future: to contain only those paint nodes
that actually contribute to the output's image.
As nothing actually supports color transforms yet, both renderers and
the DRM-backend assert that they only get identity transforms. This
check has the side-effect that all surface-output pairs actually get a
weston_surface_color_transform_ref even though it points to NULL
weston_color_transform.
This design is inspired by Sebastian Wick's Weston color management
work.
Co-authored-by: Sebastian Wick <sebastian@sebastianwick.net>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Pekka Paalanen