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color: allow creating LUT from curve even when bad precision may occur

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At this point, the DRM/KMS API supports offloading post-blend color
xform only through LUT's. This is not ideal, and an API to improve that
should be proposed in the future.

But we still want to experiment with offloading pre-blend (not post)
color transformation through the colorop API, which is close to being
accepted upstream. But this requires us to offload post-blend as well.

weston_color_curve_to_3x1D_LUT() currently fails if we detect that
crafting a LUT from the color curve may result in bad precision.
Instead, let's add a boolean param to control if we forbid or not bad
precision. This should allow us to offload post-blend xform through
LUT's.

This also improves the error messages in this function.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>
This commit is contained in:
Leandro Ribeiro 2025-05-15 15:01:08 -03:00
parent 6f969623eb
commit fceb4151a3
2 changed files with 24 additions and 5 deletions
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23
libweston/color.c
View file

@ -348,6 +348,9 @@ curve_to_lut_has_good_precision(struct weston_color_curve *curve)
* @param compositor The Weston compositor.
* @param xform The color transformation that owns the curve.
* @param step The curve step (pre or post) from the xform.
* @param precision_mode If WESTON_COLOR_PRECISION_CAREFUL, this fails if we
* detect that we can't create a LUT from the curve without resulting in
* precision issues. If WESTON_COLOR_PRECISION_CARELESS, we simply log a warning.
* @param lut_size The size of each LUT.
* @param err_msg Set on failure, untouched otherwise. Must be free()'d by caller.
* @return NULL on failure, the 3x1D LUT on success.
@ -356,10 +359,12 @@ WL_EXPORT float *
weston_color_curve_to_3x1D_LUT(struct weston_compositor *compositor,
struct weston_color_transform *xform,
enum weston_color_curve_step step,
enum weston_color_precision precision_mode,
uint32_t lut_size, char **err_msg)
{
struct weston_color_curve *curve;
float divider = lut_size - 1;
const char *step_str;
float *in, *lut;
unsigned int i, ch;
bool ret;
@ -367,18 +372,25 @@ weston_color_curve_to_3x1D_LUT(struct weston_compositor *compositor,
switch(step) {
case WESTON_COLOR_CURVE_STEP_PRE:
curve = &xform->pre_curve;
step_str = "pre";
break;
case WESTON_COLOR_CURVE_STEP_POST:
curve = &xform->post_curve;
step_str = "post";
break;
default:
weston_assert_not_reached(compositor, "unknown curve step");
}
if (!curve_to_lut_has_good_precision(curve)) {
str_printf(err_msg, "can't create color LUT from curve, it would " \
"result in bad precision");
return NULL;
if (precision_mode == WESTON_COLOR_PRECISION_CAREFUL) {
str_printf(err_msg, "can't create color LUT from xform (id %u) " \
"%s-curve, it would result in bad precision",
xform->id, step_str);
return NULL;
}
weston_log("WARNING: converting xform (id %u) %s-curve to 3x1D LUT should probably " \
"result in bad precision\n", xform->id, step_str);
}
switch(curve->type) {
@ -398,8 +410,9 @@ weston_color_curve_to_3x1D_LUT(struct weston_compositor *compositor,
if (!ret) {
free(lut);
lut = NULL;
str_printf(err_msg, "can't create color LUT from " \
"curve, failed to sample color curve");
str_printf(err_msg, "can't create color LUT from xform (id %u) " \
"%s-curve, failed to sample color curve",
xform->id, step_str);
break;
}
}

6
libweston/color.h
View file

@ -648,10 +648,16 @@ enum weston_color_curve_step {
WESTON_COLOR_CURVE_STEP_POST,
};
enum weston_color_precision {
WESTON_COLOR_PRECISION_CARELESS,
WESTON_COLOR_PRECISION_CAREFUL,
};
float *
weston_color_curve_to_3x1D_LUT(struct weston_compositor *compositor,
struct weston_color_transform *xform,
enum weston_color_curve_step step,
enum weston_color_precision precision_mode,
uint32_t lut_size, char **err_msg);
void