造二維構圖

以程式生二維圖形：SVG 構建、圖表佈局演算法、影像合成、批次處理流。涵向量圖形生成、點陣圖像處理、字體排印，與圖表、示意圖、資訊圖之自動化產出。

適用時機

• 以程式生示意圖、流程圖、資訊圖
• 造可重現之科學圖或出版圖
• 自動化產出徽章、圖示、視覺資產
• 合成多圖像或資料可視化
• 建標準庫所無之自訂圖表型
• 以參數變動批次生圖
• 為網頁或印刷造 SVG 範本

輸入

步驟

1. 立 Python 環境

裝二維構圖所需之庫：

# Core libraries
pip install svgwrite pillow cairosvg

# Optional: advanced features
pip install drawsvg reportlab pycairo

# For data-driven graphics
pip install matplotlib numpy pandas

預期： 庫裝成 失敗時： 察 Python 版本（3.7+），用虛擬環境以避衝突

2. 造基本 SVG 圖形

以 svgwrite 生 SVG：

import svgwrite
from svgwrite import cm, mm

def create_basic_svg(output_path):
    """Create a simple SVG graphic."""
    # Initialize drawing (use mm for precise dimensions)
    dwg = svgwrite.Drawing(output_path, size=('180mm', '120mm'), profile='full')

    # Add background rectangle
    dwg.add(dwg.rect(
        insert=(0, 0),
        size=('100%', '100%'),
        fill='white'
    ))

    # Add shapes
    dwg.add(dwg.circle(
        center=(90*mm, 60*mm),
        r=30*mm,
        fill='lightblue',
        stroke='navy',
        stroke_width=2
    ))

    dwg.add(dwg.rect(
        insert=(30*mm, 30*mm),
        size=(60*mm, 40*mm),
        fill='lightgreen',
        stroke='darkgreen',
        stroke_width=2,
        rx=5,  # Rounded corners
        ry=5
    ))

    # Add text
    dwg.add(dwg.text(
        'Example Graphic',
        insert=(90*mm, 20*mm),
        text_anchor='middle',
        font_size='18pt',
        font_family='Arial',
        fill='black'
    ))

    dwg.save()
    print(f"Saved: {output_path}")

預期： SVG 檔已生，含形狀與文字 失敗時： 察 svgwrite 版本，驗輸出目錄可寫

3. 以佈局邏輯建示意圖

以算出之位造結構化示意圖：

def create_flowchart(steps, output_path):
    """Generate a flowchart from list of steps."""
    dwg = svgwrite.Drawing(output_path, size=('800px', '600px'))

    # Layout parameters
    box_width = 120
    box_height = 60
    spacing_y = 100
    start_x = 340
    start_y = 50

    for i, step in enumerate(steps):
        y_pos = start_y + i * spacing_y

        # Draw box
        box = dwg.add(dwg.g(id=f'step_{i}'))

        box.add(dwg.rect(
            insert=(start_x, y_pos),
            size=(box_width, box_height),
            fill='lightblue',
            stroke='navy',
            stroke_width=2,
            rx=5,
            ry=5
        ))

        # Add text (wrapped if needed)
        text_lines = wrap_text(step, max_width=16)
        text_y = y_pos + box_height/2 - (len(text_lines)-1) * 7

        for j, line in enumerate(text_lines):
            box.add(dwg.text(
                line,
                insert=(start_x + box_width/2, text_y + j*14),
                text_anchor='middle',
                font_size='12pt',
                font_family='Arial',
                fill='black'
            ))

        # Draw arrow to next step
        if i < len(steps) - 1:
            arrow_start_y = y_pos + box_height
            arrow_end_y = y_pos + spacing_y

            dwg.add(dwg.line(
                start=(start_x + box_width/2, arrow_start_y),
                end=(start_x + box_width/2, arrow_end_y),
                stroke='black',
                stroke_width=2,
                marker_end=dwg.marker(
                    id='arrow',
                    viewBox='0 0 10 10',
                    refX=5,
                    refY=5,
                    markerWidth=6,
                    markerHeight=6,
                    orient='auto'
                )
            ))

    dwg.save()

def wrap_text(text, max_width=20):
    """Simple text wrapping."""
    words = text.split()
    lines = []
    current_line = []

    for word in words:
        test_line = ' '.join(current_line + [word])
        if len(test_line) <= max_width:
            current_line.append(word)
        else:
            if current_line:
                lines.append(' '.join(current_line))
            current_line = [word]

    if current_line:
        lines.append(' '.join(current_line))

    return lines

預期： 流程圖已生，含相連之方塊與箭頭 失敗時： 調佈局計算，驗箭頭標記之定義

4. 合成點陣圖像

以 Pillow 合多圖：

from PIL import Image, ImageDraw, ImageFont, ImageFilter
import os

def composite_images(image_paths, output_path, layout='grid'):
    """Composite multiple images into single output."""
    # Load images
    images = [Image.open(path) for path in image_paths]

    if layout == 'grid':
        # Calculate grid dimensions
        n = len(images)
        cols = int(n ** 0.5)
        rows = (n + cols - 1) // cols

        # Get max dimensions
        max_width = max(img.width for img in images)
        max_height = max(img.height for img in images)

        # Create composite canvas
        canvas_width = cols * max_width
        canvas_height = rows * max_height
        composite = Image.new('RGB', (canvas_width, canvas_height), 'white')

        # Paste images
        for i, img in enumerate(images):
            row = i // cols
            col = i % cols
            x = col * max_width
            y = row * max_height
            composite.paste(img, (x, y))

    elif layout == 'horizontal':
        # Horizontal concatenation
        total_width = sum(img.width for img in images)
        max_height = max(img.height for img in images)
        composite = Image.new('RGB', (total_width, max_height), 'white')

        x_offset = 0
        for img in images:
            composite.paste(img, (x_offset, 0))
            x_offset += img.width

    elif layout == 'vertical':
        # Vertical concatenation
        max_width = max(img.width for img in images)
        total_height = sum(img.height for img in images)
        composite = Image.new('RGB', (max_width, total_height), 'white')

        y_offset = 0
        for img in images:
            composite.paste(img, (0, y_offset))
            y_offset += img.height

    composite.save(output_path)
    print(f"Saved composite: {output_path}")

def add_annotations(image_path, annotations, output_path):
    """Add text annotations to image."""
    img = Image.open(image_path)
    draw = ImageDraw.Draw(img)

    # Load font
    try:
        font = ImageFont.truetype("Arial.ttf", 24)
    except:
        font = ImageFont.load_default()

    for annotation in annotations:
        text = annotation['text']
        position = annotation['position']
        color = annotation.get('color', 'black')

        # Add text shadow for readability
        shadow_offset = 2
        draw.text(
            (position[0] + shadow_offset, position[1] + shadow_offset),
            text,
            font=font,
            fill='white'
        )
        draw.text(position, text, font=font, fill=color)

    img.save(output_path)

預期： 合成圖已生，佈局得宜 失敗時： 察輸入圖皆在、驗圖像模式相容

5. 生資料驅動之圖形

自資料造可視化：

import numpy as np

def create_bar_chart_svg(data, labels, output_path):
    """Generate SVG bar chart from data."""
    dwg = svgwrite.Drawing(output_path, size=('600px', '400px'))

    # Chart area
    margin = 50
    chart_width = 500
    chart_height = 300
    bar_spacing = 10

    # Calculate bar dimensions
    n_bars = len(data)
    bar_width = (chart_width - (n_bars - 1) * bar_spacing) / n_bars

    # Scale data to fit chart
    max_value = max(data)
    scale = chart_height / max_value

    # Draw axes
    dwg.add(dwg.line(
        start=(margin, margin),
        end=(margin, margin + chart_height),
        stroke='black',
        stroke_width=2
    ))
    dwg.add(dwg.line(
        start=(margin, margin + chart_height),
        end=(margin + chart_width, margin + chart_height),
        stroke='black',
        stroke_width=2
    ))

    # Draw bars
    for i, (value, label) in enumerate(zip(data, labels)):
        x = margin + i * (bar_width + bar_spacing)
        bar_height = value * scale
        y = margin + chart_height - bar_height

        # Bar
        dwg.add(dwg.rect(
            insert=(x, y),
            size=(bar_width, bar_height),
            fill='steelblue',
            stroke='navy',
            stroke_width=1
        ))

        # Value label
        dwg.add(dwg.text(
            f'{value:.1f}',
            insert=(x + bar_width/2, y - 5),
            text_anchor='middle',
            font_size='10pt',
            fill='black'
        ))

        # X-axis label
        dwg.add(dwg.text(
            label,
            insert=(x + bar_width/2, margin + chart_height + 20),
            text_anchor='middle',
            font_size='10pt',
            fill='black'
        ))

    dwg.save()

預期： SVG 長條圖已生，資料已縮放 失敗時： 處邊界案（空資料、負值），加驗證

6. 批次生圖

自動化多圖之造：

def batch_generate_badges(users, template_path, output_dir):
    """Generate badge for each user."""
    os.makedirs(output_dir, exist_ok=True)

    for user in users:
        output_path = os.path.join(output_dir, f"{user['id']}_badge.svg")

        dwg = svgwrite.Drawing(output_path, size=('300px', '100px'))

        # Background
        dwg.add(dwg.rect(
            insert=(0, 0),
            size=('100%', '100%'),
            fill='#3366cc',
            rx=10,
            ry=10
        ))

        # User name
        dwg.add(dwg.text(
            user['name'],
            insert=(150, 40),
            text_anchor='middle',
            font_size='20pt',
            font_weight='bold',
            fill='white'
        ))

        # User role
        dwg.add(dwg.text(
            user['role'],
            insert=(150, 70),
            text_anchor='middle',
            font_size='14pt',
            fill='lightblue'
        ))

        dwg.save()
        print(f"Generated badge: {output_path}")

預期： 各資料項皆生獨立圖形 失敗時： 察資料結構，缺欄以預設值處之

7. SVG 轉點陣

匯 SVG 為 PNG/PDF 以供多用：

import cairosvg

def svg_to_png(svg_path, png_path, dpi=300):
    """Convert SVG to PNG with specified DPI."""
    # Calculate pixel dimensions from DPI
    # Assuming A4 size as example
    width_inches = 8.27
    height_inches = 11.69

    width_px = int(width_inches * dpi)
    height_px = int(height_inches * dpi)

    cairosvg.svg2png(
        url=svg_path,
        write_to=png_path,
        output_width=width_px,
        output_height=height_px
    )
    print(f"Converted to PNG: {png_path}")

def svg_to_pdf(svg_path, pdf_path):
    """Convert SVG to PDF."""
    cairosvg.svg2pdf(url=svg_path, write_to=pdf_path)
    print(f"Converted to PDF: {pdf_path}")

預期： 點陣輸出已生於指定解析度 失敗時： 若缺則裝 cairo 系統庫，察 SVG 之有效性

驗證清單

• 圖形於目標應用中渲染無誤
• 文字可讀且位置得宜
• 色合規格（察十六進制碼）
• 尺寸合用例
• SVG 合標準（若需）
• 點陣匯出 DPI 正確
• 佈局適應資料變動
• 批次處理完而無誤
• 輸出檔分組得宜
• 程式含誤處理

常見陷阱

1. 單位之惑：SVG 單位（px、mm、cm）與螢幕像素、印刷 DPI 之別
2. 文字溢：文字超形狀邊界；宜施換行
3. 字體可得：系統字體或異，宜內嵌或用網安之字體
4. 座標計：網格佈局中之差一錯
5. 色格式：SVG 用十六進制字串（#rrggbb），非元組
6. SVG 有效性：察 XML 結構，閉所有標籤
7. 檔路：處特殊字元與檔名中之空
8. 記憶體用：大批次操作或需分塊
9. 比例：改尺寸時保比
10. 透明：PNG 支援 alpha，JPEG 則否

相關技能

• render-publication-graphic：出版專屬之輸出需求
• create-3d-scene：三維之類似程式化法
• generate-quarto-report：整合圖形於報告中