feat: use back_design for back rendering in export

backend/apps/exports/utils.py

@@ -66,6 +66,15 @@ def get_effective_design(project, card_key):
     return base
 
 
+def get_effective_back_design(project):
+    """获取背面设计配置，合并 back_design 与 card_overrides['back']"""
+    base = dict(project.back_design or {})
+    overrides = (project.card_overrides or {}).get('back', {})
+    if overrides:
+        base.update(overrides)
+    return base
+
+
 def load_image_safe(file_path):
     """加载图片，找不到时返回 None"""
     if not file_path:
@@ -373,9 +382,13 @@ def draw_joker(canvas, design, which, project, card_key, asset):
     canvas.alpha_composite(block, (w - tw - 4 - pad, h - 2 * th - 6 - pad))
 
 
-def draw_back(canvas, design, asset):
-    """绘制背面：素材图 + 位置微调，无素材时退化为文字"""
+def draw_back(canvas, back_design, asset):
+    """绘制背面：素材图 + 位置微调 + 色调叠加，无素材时退化为文字"""
     w, h = canvas.size
+    # 填充背景色
+    bg_color = back_design.get('background_color', '#1A237E') or '#1A237E'
+    canvas.paste(hex_to_rgba(bg_color, 255), (0, 0, w, h))
+
     body_pad_x = int(w * 0.15)
     body_pad_y_top = int(h * 0.18)
     body_pad_y_bot = int(h * 0.22)
@@ -384,9 +397,9 @@ def draw_back(canvas, design, asset):
 
     if asset:
         try:
-            image_dx = float(design.get('image_dx', 0))
-            image_dy = float(design.get('image_dy', 0))
-            image_scale = float(design.get('image_scale', 1))
+            image_dx = float(back_design.get('image_dx', 0))
+            image_dy = float(back_design.get('image_dy', 0))
+            image_scale = float(back_design.get('image_scale', 1))
             offset_x = int(body_w * image_dx)
             offset_y = int(body_h * image_dy)
 
@@ -399,13 +412,26 @@ def draw_back(canvas, design, asset):
             x = body_pad_x + offset_x + (body_w - img.width) // 2
             y = body_pad_y_top + offset_y + (body_h - img.height) // 2
             canvas.alpha_composite(img, (x, y))
+
+            # 色调叠加
+            pattern_color = back_design.get('pattern_color')
+            if pattern_color:
+                tint = Image.new('RGBA', (w, h), hex_to_rgba(pattern_color, 80))
+                canvas.alpha_composite(tint)
         except Exception:
             pass
     else:
+        # 退化：绘制边框 + 文字
+        border_color = back_design.get('border_color', '#C0A050') or '#C0A050'
         draw = ImageDraw.Draw(canvas)
+        border_width = int(back_design.get('border_width', 3) or 3)
+        if border_width > 0:
+            half = max(1, border_width // 2)
+            draw.rectangle(((half, half), (w - half, h - half)),
+                           outline=hex_to_rgba(border_color, 255), width=border_width)
         fnt = make_text_font('Times New Roman', max(40, int(h * 0.08)), bold=True)
         text = 'CARD BACK'
-        color = hex_to_rgba(design.get('border_color', '#333333'), 255)
+        color = hex_to_rgba(border_color, 255)
         bb = draw.textbbox((0, 0), text, font=fnt)
         tw, th = bb[2] - bb[0], bb[3] - bb[1]
         draw.text(((w - tw) // 2, (h - th) // 2), text, font=fnt, fill=color)
@@ -439,12 +465,14 @@ def generate_card_png(project, card_key, resolution='standard'):
             break
         draw_joker(canvas, design, which, project, card_key, asset)
     elif card_key in ('back', 'card-back'):
+        back_design = get_effective_back_design(project)
         back_asset = None
         for a in project.assets.filter(asset_type='back'):
             p = os.path.join('media', a.file_path) if a.file_path else None
             back_asset = load_image_safe(p) if p else None
             break
-        draw_back(canvas, design, back_asset)
+        draw_back(canvas, back_design, back_asset)
+        return canvas
     else:
         # 'suit-rank'
         parts = card_key.split('-')