SceneKit Tutorial Part 3 - Geometry and Material

When I was writing this part of SceneKit Tutorial, Xcode 6.0 GM was released. Compared to former Xcode 6.0 beta versions, Xcode 6.0 GM start supporting iPhone6 and iPhone 6 plus iOS simulators:

New iPhone simulators

 Alright, let me start the main topics of this tutorial. In this part, I will show you some subclasses of SCNGeometry. These subclasses presents kinds of geometry shapes like Sphere, Pyramid, Tube etc. Besides that, I will present the material property of the geometry shapes in SceneKit. The material property of a geometry shape refers to a list of objects of SCNMaterial class. To make a material shown up, we need attach the material to a geometry shape first, then connect the shape to a SCNNode and then put the object of SCNNode into an object of SCNScene.

Everyone can get the source code of Part 3 of SceneKit Tutorial at this link.

You may have seen that I created a box in Part 2.  At first of this part, I will show you two types of geometry shapes: Sphere and Pyramid. Similar to box I've shown before, we use SCNSphere and SCNPyramid to create the two types of shapes:


And then put a camera to view the two shapes:

Here we use the default light from scene, so the geometry figures will look like this:

Really Plain Sphere and Pyramid

OK, it is really plain for the two shapes. We want to add more colors and  textures on the two figures. How to do that? We can add materials to the geometry shapes. Here we use these code to add stars to the geometry:

Now the program will show something like this:

Sphere and Pyramid with Star

One thing I want to mention that when assigning materials to a geometry shape, we use a list of materials. Which means we can assign several materials to a shape. But, not all the materials can be shown up. That depends on how many surface a geometry shape could have. For example, if we assign 2 materials to a sphere, because a sphere has only one surface so the second material in the list will be discarded. Here let me try to create another material with a single color and assign two materials to both sphere and pyramid:

Now one side of the pyramid will looks different, but the sphere keeps the same:

After assigning 2 materials to Sphere and Pyramid

Well, you may say that the 2 figures looks so plain and ugly. The reflective property of SCNMaterial can make the figures looks better. Which means, when the light shining on the geometry shape, the material could reflect something so that the geometry looks more like a real object. For example, I want to the Star image reflect blue light and the blue surface to reflect white light, the code looks like:

myStar.reflective.contents = UIColor.blueColor()

myBlue.reflective.contents = UIColor.whiteColor()

Now the scene will look like this:

Geometry Shapes with Reflective Materials

OK, next I will show you some other subclasses of SCNGeometry, these shapes have there specific features than others.

SCNFloor is usually used in a scene as an infinite plain. In a game it usually shows a wall, a background or a land. Objects of SCNFloor has the feature of reflection, so you can see the shadow of the shapes above and beneath the floor. To create a simple floor, here is the code:


Now the scene will looks like this:

Add a Floor to the Scene

Now let me introduce some properties of reflection of SCNFloor.

//

// Use reflectivity properties of SCNFloor

//

myFloor.reflectivity = 0.9

myFloor.reflectionResolutionScaleFactor = 1.0

myFloor.reflectionFalloffStart = 2.0

myFloor.reflectionFalloffEnd = 10.0

Here the property reflectivity specifies the contrast of the reflection compared to the original object. If its value equals to 1,  the floor looks like a mirror.

The property reflectionResolutionScaleFactor specifies the resolution scale factor of the buffer used to render the reflection, the bigger value will cost more effort to render the reflection.

The property reflectionFalloffStart specifies the distance from the floor where scene contents are reflected at full intensity, and reflectionFalloffEnd specifies the distance from the floor where scene contents are no longer reflected.

By using the values from above code, the result will looks like this:

Effect of a Floor with Reflection Properties

Now let's add materials to the floor, remember that the floor only have one surface, so we can just only see one materials if we assign more than one materials to the geometry:

myFloor.materials = [myStar, myBlue]

It will be:

Set Material to the Floor

If you see the floor from another side of surface(from the space beneath the floor), the floor will be invisible:

Ah, the floor disappeared seen from the another side of the floor.

OK, now the discussion on SCNFloor stops here. Let me introduce another useful subclass of SCNText,  this is used for creating 3D texts in the scene. To create some words in the scene, here is an example:

From above code, we initialized an object of SCNText with a string that will be shown in the scene. And set the font of the string in line 5 and the material of the string in line 6. By setting the text's orientation and position, the stuff in the scene will looks like this:

Add Text in the Scene

It is really cool, isn't it? We can see the reflection of the text on the floor.

This part will end at here. In next part, I will dig into the animation in SceneKit.