Add aspect_ratio() function that reads image size from file

- To be able to find an image file with relative path, the directory
  of the .gv file output is injected into each Image data object.
- aspect_ratio() prints a warning and returns 1:1 ratio if it fails.

src/wireviz/DataClasses.py

@@ -3,12 +3,14 @@
 
 from typing import Optional, List, Any, Union
 from dataclasses import dataclass, field
-from wireviz.wv_helper import int2tuple
+from pathlib import Path
+from wireviz.wv_helper import int2tuple, aspect_ratio
 from wireviz import wv_colors
 
 
 @dataclass
 class Image:
+    gv_dir: Path # Directory of .gv file injected as context during parsing
     # Attributes of the image object <img>:
     src: str
     scale: Optional[str] = None  # false | true | width | height | both
@@ -35,10 +37,10 @@ class Image:
             # If only one dimension is specified, compute the other because both are required.
             if self.height:
                 if not self.width:
-                    self.width = self.height # Assuming 1:1 aspect ratio for now.
+                    self.width = self.height * aspect_ratio(self.gv_dir.joinpath(self.src))
             else:
                 if self.width:
-                    self.height = self.width # Assuming 1:1 aspect ratio for now.
+                    self.height = self.width / aspect_ratio(self.gv_dir.joinpath(self.src))
 
 
 @dataclass

src/wireviz/wireviz.py

@@ -44,6 +44,11 @@ def parse(yaml_input: str, file_out: (str, Path) = None, return_types: (None, st
             if len(yaml_data[sec]) > 0:
                 if ty == dict:
                     for key, attribs in yaml_data[sec].items():
+                        # The Image dataclass might need to open an image file with a relative path.
+                        image = attribs.get('image')
+                        if isinstance(image, dict):
+                            image['gv_dir'] = Path(file_out if file_out else '').parent # Inject context
+
                         if sec == 'connectors':
                             if not attribs.get('autogenerate', False):
                                 harness.add_connector(name=key, **attribs)

src/wireviz/wv_helper.py

@@ -158,6 +158,21 @@ def open_file_write(filename):
 def open_file_append(filename):
     return open(filename, 'a', encoding='UTF-8')
 
+
+def aspect_ratio(image_src):
+    try:
+        from PIL import Image
+        image = Image.open(image_src)
+        if image.width > 0 and image.height > 0:
+            return image.width / image.height
+        print(f'aspect_ratio(): image size is {image.width} x {image.height}')
+    except ModuleNotFoundError as error:
+        print(f'aspect_ratio(): {error}')
+    except FileNotFoundError as error:
+        print(f'aspect_ratio(): {error}')
+    return 1 # Assume 1:1 when unable to read actual image size
+
+
 def manufacturer_info_field(manufacturer, mpn):
     if manufacturer or mpn:
         return f'{manufacturer if manufacturer else "MPN"}{": " + str(mpn) if mpn else ""}'