demo_utils/imread_pil.py: return demo pattern if pillow is not installed

bindings/imgui_bundle/demos_python/demo_utils/imread_pil.py

@@ -2,9 +2,63 @@
 from numpy.typing import NDArray
 
 
+_HAS_PIL = False
+try:
+    from PIL import Image
+    _HAS_PIL = True
+except ImportError:
+    import logging
+    logging.error("""
+        pillow is required to read images for Dear ImGui Bundle demo (using demo pattern instead). Install it with:
+            pip install pillow   # or conda install pillow
+        """)
+
+
+def _dummy_image(with_alpha: bool) -> NDArray[np.uint8]:
+    """
+    Generates a 400x400 RGBA image with a visually appealing sine wave interference pattern
+    and a transparent background.
+    """
+    width, height = 400, 400
+
+    # Create a grid of x and y coordinates
+    x = np.linspace(-1 * np.pi, 1 * np.pi, width)
+    y = np.linspace(-1 * np.pi, 1 * np.pi, height)
+    X, Y = np.meshgrid(x, y)
+
+    # Calculate sine wave interference pattern
+    pattern = np.sin(X**2 + Y**2) + np.sin(3 * X + 2.5 * Y)
+
+    # Normalize the pattern to range [0, 1]
+    normalized_pattern = (pattern - pattern.min()) / (pattern.max() - pattern.min())
+
+    # Map the pattern to RGB colors
+    R = (np.sin(2 * np.pi * normalized_pattern) * 127 + 128).astype(np.uint8)
+    G = (np.cos(3 * np.pi * normalized_pattern + np.pi / 2) * 127 + 128).astype(np.uint8)
+    B = (np.sin(2 * np.pi * normalized_pattern + np.pi) * 127 + 128).astype(np.uint8)
+
+    # Combine into an RGB image
+    rgb_image = np.dstack((R, G, B))
+
+    if not with_alpha:
+        return rgb_image
+
+    # Create an alpha channel: fully opaque for non-zero patterns
+    alpha = (normalized_pattern > 0.15).astype(np.uint8) * 255
+
+    # Combine RGB and alpha channels into RGBA
+    rgba_image = np.dstack((rgb_image, alpha))
+
+    return rgba_image
+
+
+
+
 def imread_pil(image_file: str, convert_to_bgr: bool = False, load_alpha: bool = False) -> NDArray[np.uint]:
     """Read an image from a file using PIL, returns a numpy array."""
-    from PIL import Image
+    if not _HAS_PIL:
+        return _dummy_image(load_alpha)
+
     image_pil = Image.open(image_file)
 
     def rgb_to_bgr(image: NDArray[np.uint]) -> NDArray[np.uint]: