[ui] Viewer3D: add support for vertex-colored meshes

Use PerVertexColorMaterial if any vertex color data is available on a mesh without textures.

meshroom/ui/components/scene3D.py

@@ -45,6 +45,13 @@ class Scene3DHelper(QObject):
             count += sum([attr.count() for attr in geo.attributes() if attr.name() == "vertexPosition"])
         return count / 3
 
+    @Slot(Qt3DCore.QEntity, result=int)
+    def vertexColorCount(self, entity):
+        count = 0
+        for geo in entity.findChildren(Qt3DRender.QGeometry):
+            count += sum([attr.count() for attr in geo.attributes() if attr.name() == "vertexColor"])
+        return count
+
 
 class TrackballController(QObject):
     """

meshroom/ui/qml/Viewer3D/MaterialSwitcher.qml

@@ -62,7 +62,11 @@ Entity {
             },
             State {
                 name: "Textured"
-                PropertyChanges { target: m; material: diffuseMap ? textured : solid }
+                PropertyChanges {
+                    target: m;
+                    // "textured" material resolution order: diffuse map > vertex color data >  no color info
+                    material: diffuseMap ? textured : (Scene3DHelper.vertexColorCount(root.parent) ? colored : solid)
+                }
             }
         ]
     }
@@ -80,6 +84,11 @@ Entity {
         diffuse: root.diffuseColor
     }
 
+    PerVertexColorMaterial {
+        id: colored
+        objectName: "VertexColorMaterial"
+    }
+
     DiffuseSpecularMaterial {
         id: textured
         objectName: "TexturedMaterial"