refactor(backend): clean up package re-exports, settings model properties, and unused signals

src/pygui/backend/visualization/chart_geometry.py

@@ -0,0 +1,33 @@
+"""Pure coordinate-mapping math shared by the QQuickPaintedItem chart items
+(GraphQuickItem, TrendChartItem). No QPainter or Qt-widget dependency, so
+it's testable without a GUI — unlike the paint() methods that call it.
+"""
+from __future__ import annotations
+
+
+def value_to_pixel(
+    value: float,
+    value_min: float,
+    value_max: float,
+    pixel_start: float,
+    pixel_span: float,
+) -> float:
+    """Map a value onto a pixel range, inverted so larger values sit at
+    smaller pixel coordinates (screen y grows downward).
+
+    Also used for evenly-spaced tick indices: pass the tick index as
+    `value` and `(tick_count - 1)` as `value_max` with `value_min=0`.
+    """
+    value_range = value_max - value_min
+    if value_range < 1e-9:
+        return pixel_start + pixel_span / 2
+    fraction = 1.0 - (value - value_min) / value_range
+    return pixel_start + fraction * pixel_span
+
+
+def index_to_pixel(index: float, count: int, pixel_start: float, pixel_span: float) -> float:
+    """Map a 0-based sample index onto a pixel range, left to right."""
+    if count <= 1:
+        return pixel_start + pixel_span / 2
+    fraction = index / (count - 1)
+    return pixel_start + fraction * pixel_span