Auto-calculate layout column count by default

If both row and column count are set to 0, pick 2 columns when rendering
5 or more tracks.

corrscope/corrscope.py

@@ -137,7 +137,7 @@ def template_config(**kwargs) -> Config:
         ),
         channels=[],
         default_label=DefaultLabel.FileName,
-        layout=LayoutConfig(orientation="v", stereo_orientation="v", ncols=1),
+        layout=LayoutConfig(orientation="v", stereo_orientation="v", ncols=0),
         render=RendererConfig(
             1920,
             1080,

corrscope/layout.py

@@ -27,7 +27,9 @@ V = Orientation.v
 OVERLAY = StereoOrientation.overlay
 
 
-class LayoutConfig(DumpableAttrs, always_dump="orientation stereo_orientation"):
+class LayoutConfig(
+    DumpableAttrs, always_dump="orientation stereo_orientation nrows ncols"
+):
     orientation: Orientation = attr.ib(default="h", converter=Orientation)
     nrows: Optional[int] = None
     ncols: Optional[int] = None
@@ -45,9 +47,6 @@ class LayoutConfig(DumpableAttrs, always_dump="orientation stereo_orientation"):
         if self.nrows and self.ncols:
             raise CorrError("cannot manually assign both nrows and ncols")
 
-        if not self.nrows and not self.ncols:
-            self.ncols = 1
-
 
 class Edges(enum.Flag):
     NONE = 0
@@ -137,21 +136,20 @@ class RendererLayout:
         cfg = self.cfg
 
         if cfg.nrows:
-            if cfg.nrows is None:
-                raise ValueError("impossible cfg: nrows is None and true")
             # nrows=0 will never occur naturally, except for a broken config with
             # nrows=0, or in unit tests which set nwaves=0 (speed_hack). To prevent
             # tests from crashing, force nrows to 1 anyway.
             nrows = min(cfg.nrows, self.nwaves) or 1
             ncols = ceildiv(self.nwaves, nrows)
         else:
-            if cfg.ncols is None:
+            # If both cfg.nrows and cfg.ncols are 0, default to auto layout.
-                raise ValueError(
+            # Set column count to 2 if we have 5 or more waves.
-                    "invalid LayoutConfig: nrows,ncols is None "
+            ncols = cfg.ncols
-                    "(__attrs_post_init__ not called?)"
+            if not ncols:
-                )
+                ncols = 2 if self.nwaves >= 5 else 1
+
             # See nrows=0 comment above.
-            ncols = min(cfg.ncols, self.nwaves) or 1
+            ncols = min(ncols, self.nwaves) or 1
             nrows = ceildiv(self.nwaves, ncols)
 
         self.wave_nrow = nrows

tests/test_layout.py

@@ -30,7 +30,8 @@ def test_layout_config():
     assert one_row
 
     default = LayoutConfig()
-    assert default.ncols == 1  # Should default to single-column layout
+    # In a default LayoutConfig, default.ncols doesn't matter. See test_auto_layout()
+    # to verify we have the right behavior.
     assert default.nrows is None
     assert default.orientation == "h"
 
@@ -117,6 +118,19 @@ def test_less_tracks_than_nrows_ncols(key, nplots):
         assert len(regions) == 1, (i, len(regions))
 
 
+@pytest.mark.parametrize("nplots", [1, 6])
+def test_auto_layout(nplots):
+    lcfg = LayoutConfig()
+    layout = RendererLayout(lcfg, [1] * nplots)
+
+    if nplots >= 6:
+        assert layout.wave_ncol == 2
+        assert layout.wave_nrow == ceildiv(nplots, 2)
+    else:
+        assert layout.wave_ncol == 1
+        assert layout.wave_nrow == nplots
+
+
 @given(
     wave_nchans=hs.lists(hs.integers(1, 10), min_size=1, max_size=100),
     orientation=hs.sampled_from(Orientation),