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render/color: replace COLOR_TRANSFORM_LUT_3D with COLOR_TRANSFORM_LCMS2

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Converting the LCMS2 transform to a 3D LUT early causes issues:

- It's a lossy process, the consumer will not be able to pick a
  3D LUT size on their own.
- It requires unnecessary conversions and allocations: an intermediate
  3D LUT is allocated, but the renderer already allocates one.
- It makes it harder to support arbitrary color transforms in the
  renderer, because each type needs to be handled differently.

Instead, expose a function to evaluate a color transform, and use
that to build the 3D LUT in the renderer.
This commit is contained in:
Simon Ser 2025-05-24 13:04:45 +02:00 • committed by Kenny Levinsen
parent 9b97e2607d
commit 3665b53e29
6 changed files with 109 additions and 111 deletions
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37
include/render/color.h
View file

@ -7,7 +7,7 @@
enum wlr_color_transform_type {
COLOR_TRANSFORM_SRGB,
COLOR_TRANSFORM_LUT_3D,
COLOR_TRANSFORM_LCMS2,
};
struct wlr_color_transform {
@ -17,37 +17,24 @@ struct wlr_color_transform {
enum wlr_color_transform_type type;
};
/**
* The formula is approximated via a 3D look-up table. A 3D LUT is a
* three-dimensional array where each element is an RGB triplet. The flat lut_3d
* array has a length of dim_len³.
*
* Color channel values in the range [0.0, 1.0] are mapped linearly to
* 3D LUT indices such that 0.0 maps exactly to the first element and 1.0 maps
* exactly to the last element in each dimension.
*
* The offset of the RGB triplet given red, green and blue indices r_index,
* g_index and b_index is:
*
* offset = 3 * (r_index + dim_len * g_index + dim_len * dim_len * b_index)
*/
struct wlr_color_transform_lut3d {
struct wlr_color_transform base;
float *lut_3d;
size_t dim_len;
};
void wlr_color_transform_init(struct wlr_color_transform *tr,
enum wlr_color_transform_type type);
/**
* Gets a wlr_color_transform_lut3d from a generic wlr_color_transform.
* Asserts that the base type is COLOR_TRANSFORM_LUT_3D
* Get a struct wlr_color_transform_lcms2 from a generic struct wlr_color_transform.
* Asserts that the base type is COLOR_TRANSFORM_LCMS2.
*/
struct wlr_color_transform_lut3d *wlr_color_transform_lut3d_from_base(
struct wlr_color_transform_lcms2 *color_transform_lcms2_from_base(
struct wlr_color_transform *tr);
void color_transform_lcms2_finish(struct wlr_color_transform_lcms2 *tr);
/**
* Evaluate a LCMS2 color transform for a given RGB triplet.
*/
void color_transform_lcms2_eval(struct wlr_color_transform_lcms2 *tr,
float out[static 3], const float in[static 3]);
/**
* Obtain primaries values from a well-known primaries name.
*/