v0.54.0: Kaleidostrobe at 60 fps, its big window on the GPU, two-tone gray mode, sync can go sooner

The plugin still steps at its own 25 fps, frame for frame; between frames
the turn continues, textures crossfade, and the cone follows a preview of
the newest audio, so beats land a refresh sooner. The big window replays
the original's GL calls through OpenGL (QPainter took ~40 ms a frame at
1080p); without GL it falls back. Gray mode is only the gray-mode colour on
the panel background. The sync slider goes to -50 ms (sooner).

tests/test_round85.py

@@ -0,0 +1,102 @@
+"""Round 85: Kaleidostrobe at 60 fps, its big window on the GPU, gray mode
+as two tones, and a sync slider that can also say "sooner".
+
+1. Between the plugin's 25 fps frames: a smooth turn, crossfaded textures,
+   the cone driven by a preview of the newest audio — which must never
+   change the original's own frames.
+2. Gray mode: the gray-mode colour on the panel background, nothing else.
+3. The sync slider below zero.
+4. The big window: an OpenGL canvas for Kaleidostrobe, QPainter without GL.
+"""
+import numpy as np
+
+from PyQt6.QtGui import QColor
+
+from lintunes.kaleidostrobe import engine as ks
+from lintunes.gui import visualizer_styles as vs
+from lintunes.gui.visualizer_kaleido import KaleidostrobeRenderer
+from lintunes.preferences import Preferences
+
+from test_round84 import GOLDEN, _digest, _frame, _paint, _FakePlayer, _LastFm
+
+
+class TestBetweenFrames:
+    def test_previews_between_frames_change_nothing(self):
+        """The renderer asks for a preview every screen refresh; the frames
+        must still be the original's."""
+        engine = ks.Kaleidostrobe(seed=1000, ticks=1000)
+        for f, (spectrum, ticks) in enumerate(zip(GOLDEN["spectra"], GOLDEN["ticks"])):
+            engine.preview(spectrum, int(ticks) + 1)
+            engine.preview(GOLDEN["spectra"][-1 - f], int(ticks) + 2)
+            frame = engine.step(spectrum, int(ticks))
+            assert _digest(frame.textures[0]) == GOLDEN["tex_digest"][f][0], f"frame {f}"
+            assert _digest(frame.textures[1]) == GOLDEN["tex_digest"][f][1], f"frame {f}"
+
+    def test_gray_mode_is_two_tone(self, qapp):
+        """Only the gray-mode colour and the panel's background, blended."""
+        r = KaleidostrobeRenderer()
+        for _ in range(5):
+            r.advance(_frame(dt=0.04))
+        r.dimmed = True                     # the widget then passes its gray
+        r.panel = QColor(240, 236, 230)
+        img = _paint(r, 120, 80, color="#606060")
+        ground, ink = np.array([240, 236, 230.]), np.array([96, 96, 96.])
+        k = (img - ground) / (ink - ground)               # 0 = ground, 1 = ink
+        assert np.ptp(k, axis=-1).max() < 0.03            # on the line between
+        assert k.min() > -0.02 and k.max() < 1.02
+        assert k.max() - k.min() > 0.3                    # and still a picture
+
+    def test_draws_between_the_plugins_frames(self, qapp):
+        """60 fps on screen: the turn moves every refresh, frames at 25."""
+        r = KaleidostrobeRenderer()
+        r.advance(_frame(dt=0.04))
+        turns, frames = [], []
+        for _ in range(12):
+            r.advance(_frame(dt=1 / 60))
+            turns.append(r._shown[0][0].turn)
+            frames.append(r._engine.frame_count)
+        assert len(set(turns)) == 12                      # every refresh
+        assert np.all(np.diff(turns) > 0)                 # smoothly onward
+        assert frames[-1] - frames[0] == 4                # 12/60 s at 25 fps
+
+class TestSyncSooner:
+    def test_negative_delay_is_kept(self):
+        assert vs.sync_delay_ms({"visualizer_sync_delay_ms": -30}) == -30
+        assert vs.sync_delay_ms({"visualizer_sync_delay_ms": -999}) == vs.SYNC_DELAY_LIMITS[0]
+
+    def test_slider_reads_sooner_and_later(self, qapp, tmp_path, monkeypatch):
+        from lintunes.gui import preferences_dialog as pd
+        monkeypatch.setattr(pd, "load_config", lambda: {})
+        dialog = pd.PreferencesDialog(Preferences(tmp_path), _LastFm())
+        assert dialog._sync_slider.minimum() < 0
+        assert pd._sync_text(-20) == "20 ms sooner"
+        assert pd._sync_text(40) == "40 ms later"
+
+
+class TestBigWindow:
+    def _vis(self, tmp_path, style):
+        from lintunes.gui.visualizer import VisualizerWidget
+        prefs = Preferences(tmp_path)
+        prefs.set("visualizer_style", style)
+        return prefs, VisualizerWidget(_FakePlayer(), prefs)
+
+    def test_kaleidostrobe_gets_the_gl_canvas(self, qapp, tmp_path):
+        prefs, vis = self._vis(tmp_path, "kaleidostrobe")
+        vis.open_big()
+        try:
+            assert vis._big._canvas is not None and not vis._big._canvas.isHidden()
+            prefs.set("visualizer_style", "bars")          # another style
+            vis._repaint()
+            assert vis._big._canvas.isHidden()
+        finally:
+            vis._big.close()
+
+    def test_without_opengl_it_paints_with_qpainter(self, qapp, tmp_path):
+        prefs, vis = self._vis(tmp_path, "kaleidostrobe")
+        vis.open_big()
+        try:
+            vis._big._canvas.unavailable.emit()             # no GL driver
+            assert vis._big._canvas.isHidden()
+            assert not vis._big._wants_gl()
+        finally:
+            vis._big.close()