In Koru you usually apply images to shapes using materials. Each side of a shape can have a material, where you can set a diffuse texture using the image you need. This works fine while the shape has proper UV mapping. Although you can setup a missed mapping directly in Koru, it doesn't always work as expected, especially for complex shapes.
For such complex shapes or if you don't want to tailor a special texture just to add a small label onto the shape, you can use decals.
Decal is basically a sticker that you can apply wherever you want. It takes the shape of the object, but also keeps its own proportions. Decals are perfect option for labels, stickers, tags and so on.
Let's start with a simple shape of a ball from the built-in shapes library:
Now scroll down the materials library to the very bottom where the images are located. You can use any image you have, but in this tutorial we'll use the built-in one for convenience. Select the iPad screen sample image and drag it onto the ball:
A popup-menu will appear that lets you either add the image as a decal or load it to the material:
Select Place as Decal item to create a decal object with the image. You will see the image is applied to the ball as a sticker. Notice the new elements in the scene tree and scene materials list:
Congratulations, you've added your first decal in Koru!
Notice the gray circle right in the middle of the decal. This is a decal gizmo that lets you control it with your mouse:
The center circle of the gizmo lets you drag the decal along the shape. The side (smaller) circle lets you rotate and scale the decal to better fit it onto the shape. Give both handles a try to see how they work, this is easy.
As you may also noticed, decal added a node to the scene tree. For more decal options you need to select this node and check the Node Properties panel:
The Node Properties panel has some special parameters for decals:
The rest parameters are exactly the same as for other nodes.
Note that Scale and Angle parameters can be configured using the gizmo and fine-tuned in the properties panel.
If you look at the scene tree, you'll notice that decal is just another node, the child node of the object it is applied to. Decal node may have one or two meshes, depending on the Double-sided option mentioned above. You can't delete or detach decal meshes, they are controlled by the decal itself.
You also can't drag decal node to another node or apply decal to another decal. This is done to ensure the internal decal management works fine.
What you can and should control is the materials of the decal meshes. After all, decal node is just a node and decal geometry is just another geometry for Koru, so you can apply materials exactly the same way, as you do for standard objects.
Decals are dead simple to add and manage, and they are the good option to add artwork to the model that doesn't have UV mapping.