sl0ppty: dim the panes you are not in, and a knob to say how much

`dim_unfocused 60`, on by default, 0 to turn it off.

The dimming itself was already possible -- `states { unfocused { dim } }` --
and deliberately not the default. The argument then was that ambient contrast
is a taste, and shipping a taste as a default is how a tool earns a
reputation for fighting you. That argument was mostly about the escape hatch:
"turn it off" meant knowing the states block exists and what a shader chain
is. A single number does not have that problem, so the objection goes away
and the default can be the one most people want.

The knob and the table are one mechanism -- the knob fills the unfocused
chain in when the config has not -- so writing the chain by hand still wins,
including writing an empty one. `states { unfocused { } }` means nothing at
all, and is not quietly refilled, which needed the parser to distinguish
"said nothing" from "said none".

60 by choice: white text lands on #c3c3c3, which reads as "not this one"
without reading as "not available", because half the time you are reading the
other pane. Picked by looking at 40, 55, 70, 90 and 120 rather than by taste
alone.

The tests that had to change are the interesting part. Six in test_shaders.py
asserted "back to green after the drag", which is no longer what normal looks
like -- and rewriting them to compare against a snapshot taken before the
drag failed too, because a drag *moves focus*: press a title and that pane is
yours, so the two panes legitimately swap appearances across one. They assert
the rule now (the pane you are in keeps its colour, the others are pushed
back), which is both what we mean and immune to the next change of defaults.

test_states.py's "an unfocused pane is left alone" is inverted, with the
reason written where the assertion used to be, because a test that flips
should say why it flipped.

1 files changed, 43 insertions, 21 deletions

diff --git a/tests/test_shaders.py b/tests/test_shaders.py
index b8e3b2c..214d4d7 100644
--- a/tests/test_shaders.py
+++ b/tests/test_shaders.py
@@ -50,6 +50,22 @@ def frame_fg(snap, pane):
     return (run or {}).get("fg")
 
 
+def check_at_rest(s, label):
+    """Assert every pane looks the way it should with nothing transient going
+    on: the one you are in keeps its colour, the others are pushed back.
+
+    Stated as the rule rather than as "the same as before the drag", because a
+    drag *moves focus* -- press a title and that pane is yours -- so the two
+    panes legitimately swap appearances across one. Comparing to a remembered
+    snapshot said they had both changed, which was true and not the point."""
+    snap = s.snapshot()
+    for p in s.panes():
+        fg = content_fg(snap, p)
+        ok = fg == GREEN if p["focused"] else fg not in (GREEN, None)
+        check(f"{label}: pane {p['id']} is at rest",
+              ok, f"{fg} (focused={p['focused']})")
+
+
 def split(s):
     s.key("\\\\")
     s.settle()
@@ -77,19 +93,35 @@ def release(s, x, y):
 
 # ---- the unfocused state ---------------------------------------------------
 
-def test_off_by_default():
+def test_the_default_dims_the_pane_you_are_not_in():
+    """`dim_unfocused` writes the unfocused chain when a config has not, so out
+    of the box the pane you left is pushed back and the one you are in is not.
+    (This asserted the opposite until the knob existed to turn it off with.)"""
     with Session(SH, cols=80, rows=14) as s:
         s.until_text("BLOCK")
         split(s)
         focused, other = by_focus(s)
         snap = s.snapshot()
-        check("by default an unfocused pane is not dimmed",
-              content_fg(snap, other) == GREEN, str(content_fg(snap, other)))
-        check("and the focused one is not either",
+        check("the unfocused pane is dimmed",
+              content_fg(snap, other) not in (GREEN, None),
+              str(content_fg(snap, other)))
+        check("and the focused one is left alone",
               content_fg(snap, focused) == GREEN,
               str(content_fg(snap, focused)))
 
 
+def test_nothing_is_dimmed_with_the_knob_at_zero():
+    with Session(SH, cols=80, rows=14, config=cfg("dim_unfocused 0\n")) as s:
+        s.until_text("BLOCK")
+        split(s)
+        focused, other = by_focus(s)
+        snap = s.snapshot()
+        check("neither pane is touched",
+              content_fg(snap, other) == GREEN and
+              content_fg(snap, focused) == GREEN,
+              f"{content_fg(snap, other)} {content_fg(snap, focused)}")
+
+
 def test_dims_everything_but_the_focused_pane():
     with Session(SH, cols=80, rows=14, config=cfg(unfocused_cfg(128))) as s:
         s.until_text("BLOCK")
@@ -168,10 +200,7 @@ def test_dragging_greys_the_other_panes():
               ch[0] == ch[2], str(grey))
 
         release(s, right["x"] + 5, right["y"] + 3)
-        snap = s.snapshot()
-        for p in s.panes():
-            check(f"pane {p['id']} is back to its own colour after the drop",
-                  content_fg(snap, p) == GREEN, str(content_fg(snap, p)))
+        check_at_rest(s, "after the drop")
 
 
 def test_full_strength_is_a_true_grey():
@@ -197,9 +226,7 @@ def test_a_press_that_never_moves_greys_nothing():
         left, right = split(s)
 
         press(s, left["x"] + 4, left["y"])
-        snap = s.snapshot()
-        check("pressing without moving greys nothing",
-              content_fg(snap, right) == GREEN, str(content_fg(snap, right)))
+        check_at_rest(s, "a press that never moved")
         release(s, left["x"] + 4, left["y"])
         s.settle(120)
 
@@ -333,10 +360,7 @@ def test_a_drag_that_ends_off_a_pane_still_clears():
         s.settle(120)
         motion(s, 0, 0)          # out into the margin
         release(s, 0, 0)
-        snap = s.snapshot()
-        for p in s.panes():
-            check(f"pane {p['id']} is un-greyed after a drop into nowhere",
-                  content_fg(snap, p) == GREEN, str(content_fg(snap, p)))
+        check_at_rest(s, "a drop into nowhere")
 
 
 def test_a_keystroke_mid_drag_clears_the_greying():
@@ -349,9 +373,7 @@ def test_a_keystroke_mid_drag_clears_the_greying():
         motion(s, right["x"] + 5, right["y"] + 3)
         s.settle(120)
         s.send("x")
-        snap = s.snapshot()
-        check("the greying goes with the drag it belonged to",
-              content_fg(snap, right) == GREEN, str(content_fg(snap, right)))
+        check_at_rest(s, "a keystroke mid-drag")
 
 
 # ---- the config block ------------------------------------------------------
@@ -424,8 +446,7 @@ def test_the_dragged_pane_can_have_a_state_of_its_own():
         check("the pane in your hand takes the dragging state",
               content_fg(snap, left) == "#0000ff", str(content_fg(snap, left)))
         release(s, right["x"] + 5, right["y"] + 3)
-        check("and gives it back on release",
-              content_fg(s.snapshot(), s.panes()[0]) == GREEN, "")
+        check_at_rest(s, "after the drop")
 
 
 def test_the_hovered_pane_is_a_different_state_from_the_rest():
@@ -527,7 +548,8 @@ def test_an_unknown_state_is_refused():
 
 
 if __name__ == "__main__":
-    test_off_by_default()
+    test_the_default_dims_the_pane_you_are_not_in()
+    test_nothing_is_dimmed_with_the_knob_at_zero()
     test_dims_everything_but_the_focused_pane()
     test_the_dimming_follows_focus()
     test_dimming_never_touches_the_chrome()