feat: add watermark to generated PDF (仅供学习参考, diagonal, semi-transparent)

app/services/pdf_generator.py

@@ -11,6 +11,7 @@ from reportlab.platypus import (
 from reportlab.pdfbase import pdfmetrics
 from reportlab.pdfbase.ttfonts import TTFont
 from reportlab.lib.enums import TA_CENTER, TA_LEFT
+from reportlab.pdfgen import canvas as pdfcanvas
 
 # 注册中文字体
 # Windows 和 Linux 使用不同路径
@@ -269,5 +270,23 @@ def generate_pdf(plan_id, student_name, content, output_dir, rendered_report=Non
                 elif line:
                     pdf.add_paragraph(line)
 
-    doc.build(pdf.elements)
+    # 水印函数（每页都绘制）
+    def draw_watermark(c, doc):
+        if not CHINESE_FONT_OK:
+            return
+        c.saveState()
+        try:
+            c.setFont("Chinese", 14)
+            # 浅灰色半透明
+            c.setFillColor(colors.Color(0.6, 0.6, 0.6, alpha=0.25))
+            # 旋转45度
+            c.translate(A4[0]/2, A4[1]/2)
+            c.rotate(45)
+            # 绘制水印文字（居中）
+            c.drawCentredString(0, 0, "仅供学习参考")
+        except Exception:
+            pass  # 字体问题则跳过水印
+        c.restoreState()
+
+    doc.build(pdf.elements, onFirstPage=draw_watermark, onLaterPages=draw_watermark)
     return output_path