feat(matplotlib): implement circlepacking-basic (#2521)

## Implementation: `circlepacking-basic` - matplotlib

Implements the **matplotlib** version of `circlepacking-basic`.

**File:** `plots/circlepacking-basic/implementations/matplotlib.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20585399783)*

---------

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/circlepacking-basic/implementations/matplotlib.py

@@ -0,0 +1,172 @@
+""" pyplots.ai
+circlepacking-basic: Circle Packing Chart
+Library: matplotlib 3.10.8 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import matplotlib.patches as patches
+import matplotlib.pyplot as plt
+import numpy as np
+
+
+# Set random seed for reproducibility
+np.random.seed(42)
+
+# Hierarchical data: Company departments with team sizes
+# Structure: {name: value} for leaves, {name: {children}} for branches
+hierarchy_data = [
+    ("Company", None, 0),  # Root
+    ("Engineering", "Company", 1),
+    ("Product", "Company", 1),
+    ("Operations", "Company", 1),
+    ("Sales", "Company", 1),
+    ("Frontend", "Engineering", 25),
+    ("Backend", "Engineering", 35),
+    ("DevOps", "Engineering", 15),
+    ("QA", "Engineering", 20),
+    ("Design", "Product", 18),
+    ("Research", "Product", 12),
+    ("PM", "Product", 8),
+    ("HR", "Operations", 10),
+    ("Finance", "Operations", 12),
+    ("Legal", "Operations", 6),
+    ("Admin", "Operations", 8),
+    ("North", "Sales", 22),
+    ("South", "Sales", 18),
+    ("Intl", "Sales", 28),
+]
+
+# Build node structure with computed values
+nodes = {}
+for name, parent, value in hierarchy_data:
+    nodes[name] = {"name": name, "parent": parent, "value": value, "children": []}
+
+# Link children to parents
+for name, node in nodes.items():
+    if node["parent"]:
+        nodes[node["parent"]]["children"].append(name)
+
+# Compute values for branch nodes (sum of children)
+for name in ["Engineering", "Product", "Operations", "Sales"]:
+    nodes[name]["value"] = sum(nodes[c]["value"] for c in nodes[name]["children"])
+nodes["Company"]["value"] = sum(nodes[c]["value"] for c in nodes["Company"]["children"])
+
+# Color scheme by depth level
+depth_colors = {
+    0: "#306998",  # Python Blue - root
+    1: "#FFD43B",  # Python Yellow - departments
+    2: "#5BA0D0",  # Light blue - teams
+}
+depth_alphas = {0: 0.3, 1: 0.7, 2: 0.7}
+
+# Circle packing layout - compute positions
+# We'll use a simple analytical approach for cleaner containment
+circles = []
+
+# Root circle
+root_radius = 280
+circles.append({"name": "Company", "x": 0, "y": 0, "radius": root_radius, "depth": 0})
+
+# Department positioning (4 departments in quadrants)
+dept_names = ["Engineering", "Product", "Operations", "Sales"]
+dept_values = [nodes[d]["value"] for d in dept_names]
+total_dept = sum(dept_values)
+
+# Position departments in a ring within root
+dept_ring_radius = root_radius * 0.52
+dept_angles = [np.pi * 0.75, np.pi * 0.25, -np.pi * 0.25, -np.pi * 0.75]
+
+dept_circles = {}
+for i, dept in enumerate(dept_names):
+    # Radius proportional to sqrt of value
+    dept_radius = np.sqrt(dept_values[i] / total_dept) * root_radius * 0.42
+    dept_x = dept_ring_radius * np.cos(dept_angles[i])
+    dept_y = dept_ring_radius * np.sin(dept_angles[i])
+    circles.append({"name": dept, "x": dept_x, "y": dept_y, "radius": dept_radius, "depth": 1})
+    dept_circles[dept] = {"x": dept_x, "y": dept_y, "radius": dept_radius}
+
+# Team positioning within each department
+for dept in dept_names:
+    children = nodes[dept]["children"]
+    if not children:
+        continue
+
+    parent = dept_circles[dept]
+    child_values = [nodes[c]["value"] for c in children]
+    total_child = sum(child_values)
+    n_children = len(children)
+
+    # Arrange children in a circle within parent
+    child_ring_radius = parent["radius"] * 0.55
+    angle_step = 2 * np.pi / n_children
+    start_angle = np.pi / 2
+
+    for j, child in enumerate(children):
+        child_radius = np.sqrt(child_values[j] / total_child) * parent["radius"] * 0.40
+        angle = start_angle + j * angle_step
+        child_x = parent["x"] + child_ring_radius * np.cos(angle)
+        child_y = parent["y"] + child_ring_radius * np.sin(angle)
+
+        # Ensure child stays within parent boundary
+        dist_to_parent_center = np.sqrt((child_x - parent["x"]) ** 2 + (child_y - parent["y"]) ** 2)
+        max_dist = parent["radius"] - child_radius - 3  # padding
+        if dist_to_parent_center + child_radius > parent["radius"] - 2:
+            scale = max_dist / dist_to_parent_center
+            child_x = parent["x"] + (child_x - parent["x"]) * scale
+            child_y = parent["y"] + (child_y - parent["y"]) * scale
+
+        circles.append({"name": child, "x": child_x, "y": child_y, "radius": child_radius, "depth": 2})
+
+# Create figure (square format for symmetric visualization)
+fig, ax = plt.subplots(figsize=(12, 12))
+
+# Draw circles from largest to smallest (painter's algorithm)
+circles_sorted = sorted(circles, key=lambda c: -c["radius"])
+
+for circle in circles_sorted:
+    color = depth_colors.get(circle["depth"], "#AAAAAA")
+    alpha = depth_alphas.get(circle["depth"], 0.7)
+
+    circ = patches.Circle(
+        (circle["x"], circle["y"]), circle["radius"], facecolor=color, edgecolor="#2C3E50", linewidth=2.5, alpha=alpha
+    )
+    ax.add_patch(circ)
+
+    # Add labels for circles that are large enough
+    if circle["radius"] > 30:
+        fontsize = min(18, max(11, circle["radius"] * 0.25))
+        # Dark text on yellow, white on other colors
+        text_color = "#1A1A1A" if circle["depth"] == 1 else "#FFFFFF"
+        ax.text(
+            circle["x"],
+            circle["y"],
+            circle["name"],
+            ha="center",
+            va="center",
+            fontsize=fontsize,
+            fontweight="bold",
+            color=text_color,
+        )
+
+# Set equal aspect ratio and limits
+ax.set_aspect("equal")
+padding = root_radius * 0.15
+ax.set_xlim(-root_radius - padding, root_radius + padding)
+ax.set_ylim(-root_radius - padding, root_radius + padding)
+
+# Remove axes for cleaner visualization
+ax.axis("off")
+
+# Title - exact format: {spec-id} · {library} · pyplots.ai
+ax.set_title("circlepacking-basic · matplotlib · pyplots.ai", fontsize=24, fontweight="bold", pad=20)
+
+# Legend with correct colors matching actual rendering
+legend_elements = [
+    patches.Patch(facecolor="#306998", edgecolor="#2C3E50", alpha=0.3, label="Company (Root)"),
+    patches.Patch(facecolor="#FFD43B", edgecolor="#2C3E50", alpha=0.7, label="Departments"),
+    patches.Patch(facecolor="#5BA0D0", edgecolor="#2C3E50", alpha=0.7, label="Teams"),
+]
+ax.legend(handles=legend_elements, loc="upper right", fontsize=16, framealpha=0.9)
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight", facecolor="white")

plots/circlepacking-basic/metadata/matplotlib.yaml

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+library: matplotlib
+specification_id: circlepacking-basic
+created: '2025-12-30T00:04:06Z'
+updated: '2025-12-30T00:23:08Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20585399783
+issue: 0
+python_version: 3.13.11
+library_version: 3.10.8
+preview_url: https://storage.googleapis.com/pyplots-images/plots/circlepacking-basic/matplotlib/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/circlepacking-basic/matplotlib/plot_thumb.png
+preview_html: null
+quality_score: 91
+review:
+  strengths:
+  - Excellent hierarchical visualization with proper nesting and containment
+  - Smart use of square figure format (12x12) appropriate for circular visualization
+  - 'Colorblind-safe palette with good visual hierarchy (root: muted blue, departments:
+    bright yellow, teams: light blue)'
+  - Proper area-based sizing using sqrt scaling for accurate visual perception
+  - Clean implementation of painter's algorithm (drawing larger circles first)
+  - Realistic organizational data that makes the visualization immediately understandable
+  - Well-positioned legend that doesn't interfere with the visualization
+  weaknesses:
+  - Team-level circles lack labels (only circles with radius > 30 get labels), making
+    it hard to identify specific teams
+  - Could benefit from showing team names at least for the larger team circles (e.g.,
+    Backend at 35 employees)