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wrlib: change default scaling interpolation to Catmull-Rom

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This patch is implementing a new default Catmull-Rom filter
to resize images.
Catmull-Rom is a special case of cubic interpolation with B=0 and
C=0.5 (in the Mitchell-Netravali formulation).
It provides slighlty sharper results than Mitchell with the same
performance.
Catmull-Rom is a better choice for a window manager as it prioritizes
sharpness, making small elements feel crisp.
This commit is contained in:
David Maciejak
2026-01-25 14:17:52 -05:00
committed by Carlos R. Mafra
parent 77db6dc649
commit 474b23344a
3 changed files with 27 additions and 5 deletions
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2
wrlib/context.c
View File

@@ -554,7 +554,7 @@ RContext *RCreateContext(Display * dpy, int screen_number, const RContextAttribu
if (!(context->attribs->flags & RC_ScalingFilter)) {
context->attribs->flags |= RC_ScalingFilter;
context->attribs->scaling_filter = RMitchellFilter;
context->attribs->scaling_filter = RCatmullRomFilter;
}
/* get configuration from environment variables */

27
wrlib/scale.c
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@@ -244,8 +244,25 @@ static double Mitchell_filter(double t)
return (0.0);
}
static double (*filterf)(double) = Mitchell_filter;
static double fwidth = Mitchell_support;
#define CatmullRom_support (2.0)
static double CatmullRom_filter(double t)
{
double tt;
tt = t * t;
if (t < 0)
t = -t;
if (t < 1.0) {
return ((1.5 * t * tt) - (2.5 * tt) + 1.0);
} else if (t < 2.0) {
return ((-0.5 * t * tt) + (2.5 * tt) - (4.0 * t) + 2.0);
}
return (0.0);
}
static double (*filterf)(double) = CatmullRom_filter;
static double fwidth = CatmullRom_support;
void wraster_change_filter(RScalingFilter type)
{
@@ -270,11 +287,15 @@ void wraster_change_filter(RScalingFilter type)
filterf = Lanczos3_filter;
fwidth = Lanczos3_support;
break;
default:
case RMitchellFilter:
filterf = Mitchell_filter;
fwidth = Mitchell_support;
break;
default:
case RCatmullRomFilter:
filterf = CatmullRom_filter;
fwidth = CatmullRom_support;
break;
}
}

3
wrlib/wraster.h.in
View File

@@ -143,7 +143,8 @@ typedef enum {
RBellFilter,
RBSplineFilter,
RLanczos3Filter,
RMitchellFilter
RMitchellFilter,
RCatmullRomFilter
} RScalingFilter;