add arrow example

scripts/arrows.py

@@ -0,0 +1,21 @@
+
+import compas
+from compas.colors import Color
+from compas.geometry import Vector
+from compas_viewer.viewer import Viewer
+
+viewer = Viewer()
+
+N = 10
+M = 10
+
+for i in range(N):
+    for j in range(M):
+        viewer.scene.add(
+            Vector(0, 0, (i + j + 1) / 5),
+            anchor = [i, j, 0],
+            linecolor=Color(i / N, j / M, 0.0),
+            name=f"Arrow_{i}_{j}",
+        )
+
+viewer.show()

src/compas_viewer/components/color.py

@@ -176,7 +176,7 @@ def __init__(
         elif isinstance(default_color, ColorDict):
             default_color = default_color.default
         else:
-            raise ValueError("Invalid color type.")
+            raise ValueError("Invalid color type. : {}".format(type(default_color)))
         default_color = QColor(*remap_rgb(default_color, to_range_one=False))
 
         self.color_button = QPushButton(self)

src/compas_viewer/components/layout.py

@@ -138,7 +138,7 @@ def set_layout(self, items: list[dict], obj: Any) -> None:
                 min_val: float = sub_item.get("min_val", None)
                 max_val: float = sub_item.get("max_val", None)
 
-                if attr and not hasattr(obj, attr):
+                if attr and getattr(obj, attr, None) is None:
                     # TODO: @Tsai, this needs to be handled at upper level.
                     continue