Simplify handling of out-of-bound values Colormap.__call__.

anntzer · anntzer · commit 29147f2bdc3a · 2023-01-14T02:58:45.000+01:00
Mostly, we don't need to manually handle/clip out of bounds float values
if we compute the masks early enough (note that these masks are always
computed at some point anyways, so there's no cost of doing that a bit
earlier).
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -708,28 +708,23 @@ def __call__(self, X, alpha=None, bytes=False):
 
         # Take the bad mask from a masked array, or in all other cases defer
         # np.isnan() to after we have converted to an array.
-        mask_bad = X.mask if np.ma.is_masked(X) else None
         xa = np.array(X, copy=True)
-        if mask_bad is None:
-            mask_bad = np.isnan(xa)
         if not xa.dtype.isnative:
             xa = xa.byteswap().newbyteorder()  # Native byteorder is faster.
         if xa.dtype.kind == "f":
             xa *= self.N
-            # Negative values are out of range, but astype(int) would
-            # truncate them towards zero.
-            xa[xa < 0] = -1
             # xa == 1 (== N after multiplication) is not out of range.
             xa[xa == self.N] = self.N - 1
-            # Avoid converting large positive values to negative integers.
-            np.clip(xa, -1, self.N, out=xa)
+        # Pre-compute the masks before casting to int (which can truncate
+        # negative values to zero or wrap large floats to negative ints).
+        mask_under = xa < 0
+        mask_over = xa > self.N - 1
+        mask_bad = X.mask if np.ma.is_masked(X) else np.isnan(xa)
         with np.errstate(invalid="ignore"):
             # We need this cast for unsigned ints as well as floats
             xa = xa.astype(int)
-        # Set the over-range indices before the under-range;
-        # otherwise the under-range values get converted to over-range.
-        xa[xa > self.N - 1] = self._i_over
-        xa[xa < 0] = self._i_under
+        xa[mask_under] = self._i_under
+        xa[mask_over] = self._i_over
         xa[mask_bad] = self._i_bad
 
         lut = self._lut
