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color,gl-renderer: handle neg. in linpow/powlin

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We can handle the mirroring for negative input without conditional this
way. Maybe it's faster, maybe it's not, but I like this style better.

In color-operations we need only one call to the elementary function
rather than two. This helps a lot with code clarity, when we get a vec3
at a time to handle in the future, doing three trivial calls instead of
six with an if-else hassle.

fragment.glsl sheds one layer of function wrapping, which is nice.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This commit is contained in:
Pekka Paalanen 2025-10-02 16:00:16 +03:00
parent bef29b8774
commit e87eb19877
2 changed files with 26 additions and 48 deletions
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24
libweston/color-operations.c
View file

@ -51,9 +51,11 @@ static float
linpow(float x, const union weston_color_curve_parametric_chan_data *p)
{
/* See WESTON_COLOR_CURVE_PARAMETRIC_TYPE_LINPOW for details about LINPOW. */
/* LINPOW uses mirroring for negative input values. */
float abs_x = fabsf(x);
if (x >= p->d)
return pow((p->a * x) + p->b, p->g);
if (abs_x >= p->d)
return copysign(pow((p->a * abs_x) + p->b, p->g), x);
return p->c * x;
}
@ -70,11 +72,7 @@ sample_linpow(const union weston_color_curve_parametric_chan_data *p,
if (clamp_input)
x = ensure_unorm(x);
/* LINPOW uses mirroring for negative input values. */
if (x < 0.0)
out[i] = -linpow(-x, p);
else
out[i] = linpow(x, p);
out[i] = linpow(x, p);
}
}
@ -82,9 +80,11 @@ static float
powlin(float x, const union weston_color_curve_parametric_chan_data *p)
{
/* See WESTON_COLOR_CURVE_PARAMETRIC_TYPE_POWLIN for details about POWLIN. */
/* POWLIN uses mirroring for negative input values. */
float abs_x = fabsf(x);
if (x >= p->d)
return p->a * pow(x, p->g) + p->b;
if (abs_x >= p->d)
return copysign(p->a * pow(abs_x, p->g) + p->b, x);
return p->c * x;
}
@ -101,11 +101,7 @@ sample_powlin(const union weston_color_curve_parametric_chan_data *p,
if (clamp_input)
x = ensure_unorm(x);
/* POWLIN uses mirroring for negative input values. */
if (x < 0.0)
out[i] = -powlin(-x, p);
else
out[i] = powlin(x, p);
out[i] = powlin(x, p);
}
}

50
libweston/renderer-gl/fragment.glsl
View file

@ -298,67 +298,49 @@ unpack_params(const parametric_curve_t par, compile_const int chan)
}
float
linpow(float x, const gabcd_t p)
linpow(const gabcd_t p, float x)
{
/* See WESTON_COLOR_CURVE_PARAMETRIC_TYPE_LINPOW for details about LINPOW. */
if (x >= p.d)
return pow((p.a * x) + p.b, p.g);
return p.c * x;
}
float
sample_linpow(const gabcd_t p, float x)
{
if (p.clamp)
x = clamp(x, 0.0, 1.0);
/* We use mirroring for negative input values. */
if (x < 0.0)
return -linpow(-x, p);
float abs_x = abs(x);
if (abs_x >= p.d)
return sign(x) * pow((p.a * abs_x) + p.b, p.g);
return linpow(x, p);
return p.c * x;
}
vec3
sample_linpow_vec3(const parametric_curve_t par, vec3 color)
{
return vec3(sample_linpow(unpack_params(par, 0), color.r),
sample_linpow(unpack_params(par, 1), color.g),
sample_linpow(unpack_params(par, 2), color.b));
return vec3(linpow(unpack_params(par, 0), color.r),
linpow(unpack_params(par, 1), color.g),
linpow(unpack_params(par, 2), color.b));
}
float
powlin(float x, const gabcd_t p)
powlin(const gabcd_t p, float x)
{
/* See WESTON_COLOR_CURVE_PARAMETRIC_TYPE_POWLIN for details about POWLIN. */
if (x >= p.d)
return p.a * pow(x, p.g) + p.b;
return p.c * x;
}
float
sample_powlin(const gabcd_t p, float x)
{
if (p.clamp)
x = clamp(x, 0.0, 1.0);
/* We use mirroring for negative input values. */
if (x < 0.0)
return -powlin(-x, p);
float abs_x = abs(x);
if (abs_x >= p.d)
return sign(x) * (p.a * pow(abs_x, p.g) + p.b);
return powlin(x, p);
return p.c * x;
}
vec3
sample_powlin_vec3(const parametric_curve_t par, vec3 color)
{
return vec3(sample_powlin(unpack_params(par, 0), color.r),
sample_powlin(unpack_params(par, 1), color.g),
sample_powlin(unpack_params(par, 2), color.b));
return vec3(powlin(unpack_params(par, 0), color.r),
powlin(unpack_params(par, 1), color.g),
powlin(unpack_params(par, 2), color.b));
}
float