feat(altair): implement rose-basic (#5596)

## Implementation: `rose-basic` - python/altair

Implements the **python/altair** version of `rose-basic`.

**File:** `plots/rose-basic/implementations/python/altair.py`

**Parent Issue:** #1003

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25151891021)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/rose-basic/implementations/python/altair.py

@@ -1,139 +1,89 @@
-""" pyplots.ai
+""" anyplot.ai
 rose-basic: Basic Rose Chart
-Library: altair 6.0.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: altair 6.1.0 | Python 3.13.13
+Quality: 87/100 | Updated: 2026-04-30
 """
 
+import os
+
 import altair as alt
 import numpy as np
 import pandas as pd
 
 
-# Data - Monthly rainfall in mm (cyclical 12-month pattern)
+# Theme
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+
+# Data - Monthly rainfall in mm (12-month cyclical pattern)
 months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
 rainfall = [78, 52, 68, 45, 35, 28, 22, 30, 55, 85, 92, 88]
 
 n = len(months)
-
-# Calculate angles starting at 12 o'clock (top) and going clockwise
-# -90 degrees offset to start at top, then proceeding clockwise
 angle_step = 360 / n
 start_angles = [-90 + i * angle_step for i in range(n)]
 end_angles = [-90 + (i + 1) * angle_step for i in range(n)]
 
-# Create DataFrame with explicit angles
 df = pd.DataFrame(
-    {
-        "month": months,
-        "value": rainfall,
-        "order": range(n),
-        "startAngle": np.radians(start_angles),
-        "endAngle": np.radians(end_angles),
-    }
+    {"month": months, "value": rainfall, "startAngle": np.radians(start_angles), "endAngle": np.radians(end_angles)}
 )
 
-# Max value for radius scaling - use 100 for nicer gridline values
 max_val = 100
+chart_radius = 460
 
-# Color palette - colorblind-friendly distinct colors
-colors = [
-    "#306998",  # Python Blue (Jan)
-    "#FFD43B",  # Python Yellow (Feb)
-    "#4ECDC4",  # Teal (Mar)
-    "#FF6B6B",  # Coral (Apr)
-    "#95E1D3",  # Mint (May)
-    "#F38181",  # Salmon (Jun)
-    "#A8D5BA",  # Sage (Jul)
-    "#FFC93C",  # Gold (Aug)
-    "#5D9CEC",  # Sky Blue (Sep)
-    "#AC92EB",  # Lavender (Oct)
-    "#EC87C0",  # Pink (Nov)
-    "#48CFAD",  # Seafoam (Dec)
-]
-
-# Create radial gridlines data (concentric circles at 25, 50, 75, 100 mm)
+# Radial gridlines at 25, 50, 75, 100 mm
 grid_values = [25, 50, 75, 100]
-grid_data = pd.DataFrame({"value": grid_values, "label": [f"{v}" for v in grid_values]})
+grid_data = pd.DataFrame({"value": grid_values})
 
-# Chart radius for the radial visualization
-chart_radius = 450
-
-# Radial gridlines - concentric circles using mark_arc
 gridlines = (
     alt.Chart(grid_data)
-    .mark_arc(filled=False, stroke="#cccccc", strokeWidth=1.5, strokeDash=[6, 4])
+    .mark_arc(filled=False, stroke=INK_SOFT, strokeWidth=1.0, strokeOpacity=0.35, strokeDash=[6, 4])
     .encode(
-        theta=alt.value(2 * np.pi),  # Full circle
+        theta=alt.value(2 * np.pi),
         radius=alt.Radius("value:Q", scale=alt.Scale(type="linear", domain=[0, max_val], range=[0, chart_radius])),
     )
 )
 
-# Grid labels positioned at 3 o'clock position (right side) to avoid overlap with data
+# Grid labels at 3 o'clock position
 grid_label_data = pd.DataFrame(
-    {
-        "value": grid_values,
-        "label": [f"{v} mm" for v in grid_values],
-        # Position labels at 3 o'clock (right) - angle = 0 degrees
-        "theta": [0.0] * len(grid_values),
-    }
+    {"value": grid_values, "label": [f"{v} mm" for v in grid_values], "theta": [0.0] * len(grid_values)}
 )
 
 grid_labels = (
     alt.Chart(grid_label_data)
-    .mark_text(fontSize=18, fontWeight="bold", dx=12, color="#666666", align="left", baseline="middle")
+    .mark_text(fontSize=18, dx=10, align="left", baseline="middle")
     .encode(
         theta=alt.Theta("theta:Q"),
         radius=alt.Radius("value:Q", scale=alt.Scale(type="linear", domain=[0, max_val], range=[0, chart_radius])),
         text="label:N",
+        color=alt.value(INK_SOFT),
     )
 )
 
-# Rose chart using mark_arc with explicit angles to start at 12 o'clock
+# Rose chart segments — viridis colormap for value-based color encoding (12 categories)
 rose = (
     alt.Chart(df)
-    .mark_arc(stroke="#ffffff", strokeWidth=2, innerRadius=0)
+    .mark_arc(stroke=PAGE_BG, strokeWidth=2, innerRadius=0)
     .encode(
         theta=alt.Theta("startAngle:Q", stack=None),
         theta2=alt.Theta2("endAngle:Q"),
         radius=alt.Radius("value:Q", scale=alt.Scale(type="linear", domain=[0, max_val], range=[0, chart_radius])),
-        color=alt.Color(
-            "month:N",
-            scale=alt.Scale(domain=months, range=colors),
-            legend=None,  # Legend disabled to control canvas size; colors are self-explanatory with labels
-        ),
+        color=alt.Color("value:Q", scale=alt.Scale(scheme="viridis"), legend=None),
         tooltip=[alt.Tooltip("month:N", title="Month"), alt.Tooltip("value:Q", title="Rainfall (mm)")],
     )
 )
 
-# Calculate label positions - midpoint angle for each segment
-mid_angles = [(-90 + (i + 0.5) * angle_step) for i in range(n)]
+# Value labels near segment tips
+mid_angles = [-90 + (i + 0.5) * angle_step for i in range(n)]
 mid_angles_rad = np.radians(mid_angles)
 
-# For small values that cluster together (Jun-Aug: 28, 22, 30), push labels further out
-# to prevent crowding; larger values can have labels closer to segment edge
-label_radii = []
-for v in rainfall:
-    if v < 35:
-        # Small segments - push label further outside segment
-        label_radii.append(max(v * 1.35, 45))
-    else:
-        # Normal segments - position just outside
-        label_radii.append(v * 1.15)
-
-# Create label data with theta and radius for polar positioning
-label_data = pd.DataFrame({"month": months, "value": rainfall, "theta": mid_angles_rad, "labelRadius": label_radii})
+label_radii = [max(v * 1.35, 45) if v < 35 else v * 1.15 for v in rainfall]
 
-# Create month labels positioned at outer edge of chart
-month_label_data = pd.DataFrame(
-    {
-        "month": months,
-        "theta": mid_angles_rad,
-        "labelRadius": [115] * n,  # Just outside the 100mm gridline
-    }
-)
+label_data = pd.DataFrame({"month": months, "value": rainfall, "theta": mid_angles_rad, "labelRadius": label_radii})
 
-# Text labels showing values on each segment using polar coordinates
-text = (
+value_labels = (
     alt.Chart(label_data)
     .mark_text(fontSize=20, fontWeight="bold")
     .encode(
@@ -142,11 +92,13 @@
             "labelRadius:Q", scale=alt.Scale(type="linear", domain=[0, max_val], range=[0, chart_radius])
         ),
         text=alt.Text("value:Q"),
-        color=alt.value("#333333"),
+        color=alt.value(INK),
     )
 )
 
-# Month labels at outer edge
+# Month labels at outer edge — just beyond the 100 mm gridline
+month_label_data = pd.DataFrame({"month": months, "theta": mid_angles_rad, "labelRadius": [115.0] * n})
+
 month_labels = (
     alt.Chart(month_label_data)
     .mark_text(fontSize=22, fontWeight="bold")
@@ -156,66 +108,23 @@
             "labelRadius:Q", scale=alt.Scale(type="linear", domain=[0, max_val], range=[0, chart_radius])
         ),
         text=alt.Text("month:N"),
-        color=alt.value("#333333"),
+        color=alt.value(INK),
     )
 )
 
 # Combine all layers
 chart = (
-    alt.layer(gridlines, grid_labels, rose, text, month_labels)
-    .properties(title=alt.Title(text="rose-basic · altair · pyplots.ai", fontSize=32, anchor="middle", offset=15))
-    .configure_view(strokeWidth=0)
+    alt.layer(gridlines, grid_labels, rose, value_labels, month_labels)
+    .properties(
+        width=1200,
+        height=1200,
+        background=PAGE_BG,
+        title=alt.Title(text="rose-basic · altair · anyplot.ai", fontSize=32, anchor="middle", offset=20, color=INK),
+    )
+    .configure_view(strokeWidth=0, fill=PAGE_BG)
     .configure_axis(grid=False, domain=False, ticks=False, labels=False, title=None)
 )
 
-# Save chart - Altair radial charts position content in upper portion
-# Use high scale factor to ensure quality, then crop to center the content
-chart.save("plot_raw.png", scale_factor=3.0)
-chart.save("plot.html")
-
-# Post-process: crop to center the radial chart and resize to 3600x3600 (square format)
-from PIL import Image
-
-
-img = Image.open("plot_raw.png")
-width, height = img.size
-
-# Altair radial charts center content horizontally but place it in the upper portion vertically
-# The radial center is approximately at 36% from the top of the rendered image
-content_center_y = int(height * 0.36)
-content_center_x = width // 2
-
-# Use a crop size that captures all content including outer month labels with some padding
-crop_size = min(width, int(height * 0.80))
-
-# Center the crop on the content
-left = content_center_x - crop_size // 2
-top = content_center_y - crop_size // 2
-right = left + crop_size
-bottom = top + crop_size
-
-# Adjust if crop extends beyond image boundaries
-if left < 0:
-    left = 0
-    right = crop_size
-if top < 0:
-    top = 0
-    bottom = crop_size
-if right > width:
-    right = width
-    left = width - crop_size
-if bottom > height:
-    bottom = height
-    top = height - crop_size
-
-cropped = img.crop((left, top, right, bottom))
-
-# Resize to target 3600x3600
-final = cropped.resize((3600, 3600), Image.Resampling.LANCZOS)
-final.save("plot.png")
-
-# Clean up temp file
-import os
-
-
-os.remove("plot_raw.png")
+# Save
+chart.save(f"plot-{THEME}.png", scale_factor=3.0)
+chart.save(f"plot-{THEME}.html")