filter_kernels: remove bcspline filter

After fixing the B and C params for bcspline, it ended up being the same
thing as bicubic. There's no reason to have two names for the same
filter, so remove bcspline and keep bicubic to match libplacebo.

DOCS/interface-changes.rst

@@ -60,6 +60,7 @@ Interface changes
     - add `--icc-3dlut-size=auto` and make it the default
     - add `--scale=ewa_lanczos4sharpest`
     - remove `--scale-wblur`, `--cscale-wblur`, `--dscale-wblur`, `--tscale-wblur`
+    - remove `bcspline` filter (`bicubic` is now the same as `bcspline`)
  --- mpv 0.36.0 ---
     - add `--target-contrast`
     - Target luminance value is now also applied when ICC profile is used.

DOCS/man/options.rst

@@ -5338,8 +5338,8 @@ them.
     filter is not tunable. Currently, this affects the following filter
     parameters:
 
-    bcspline
-        Spline parameters (``B`` and ``C``). Defaults to 0.5 for both.
+    bicubic
+        Spline parameters (``B`` and ``C``). Defaults to B=1 and C=0.
 
     gaussian
         Scale parameter (``t``). Increasing this makes the result blurrier.

video/out/filter_kernels.c

@@ -216,15 +216,6 @@ static double quadric(params *p, double x)
     return 0.0;
 }
 
-#define POW3(x) ((x) <= 0 ? 0 : (x) * (x) * (x))
-static double bicubic(params *p, double x)
-{
-    return (1.0/6.0) * (      POW3(x + 2)
-                        - 4 * POW3(x + 1)
-                        + 6 * POW3(x)
-                        - 4 * POW3(x - 1));
-}
-
 static double bessel_i0(double x)
 {
     double s = 1.0;
@@ -397,8 +388,7 @@ const struct filter_kernel mp_filter_kernels[] = {
     {{"haasnsoft", JINC_R3, jinc, .blur = 1.11, .resizable = true},
         .polar = true, .window = "hanning"},
     // Cubic filters
-    {{"bicubic",        2,   bicubic}},
-    {{"bcspline",       2,   cubic_bc, .params = {1.0, 0.0} }},
+    {{"bicubic",        2,   cubic_bc, .params = {1.0, 0.0} }},
     {{"hermite",        1,   cubic_bc, .params = {0.0, 0.0} }},
     {{"catmull_rom",    2,   cubic_bc, .params = {0.0, 0.5} }},
     {{"mitchell",       2,   cubic_bc, .params = {1.0/3.0, 1.0/3.0} }},