Cocos3D - background shown through meshes

Question

I imported the .pod file created from Blender and the blue background is shown through the eyelash and eyebrow meshes. Does anyone know why I'm encountering this?

WITHOUT additional material (looking normal except the root of the hair).

WITH new green material added to her left shoulder, the eyebrow and eyelash began showing the background

Answer 1

This issue is caused by the order in which the nodes are being rendered in your scene.

In the first model, the hair is drawn first, then the skin, then the eyebrows and eyelashes. In the second model, the hair, eyebrows and eyelashes are all drawn before the skin. By the time the skin under the hair or eyelashes is drawn, the depth buffer indicates that something closer to the camera has already been drawn, and the engine doesn't bother rendering those skin pixels. But because the eyelashes, eyebrows and hair all contain transparency, we end up looking right through them onto the backdrop.

This design use of a depth buffer is key to all 3D rendering. It's how the engine knows not to render pixels that are being visually occluded by another object, otherwise all we'd ever see was the last object to be rendered.However, when rendering overlapping objects that contain transparency, it's important to get the rendering order correct, so that more distant objects that are behind closer transparent objects are rendered first.

In Cocos3D, there are several tool available for you to order your transparent objects for rendering:

1. The first, and primary tool, is the drawingSequencer that is managed by the CC3Scene. You can configure several different types of drawing sequencers. The default sequencer is smart enough to render all opaque objects first, then to render the objects that contain transparency in decreasing order of distance from the camera (rendering farther objects first). This works best for most scenes, and in particular where objects are moving around and can move in front of each other unpredictably. Unfortunately, in your custom CC3Scene initialization code (which you sent me per the question comments), you replaced the default drawing sequencer with one that does not sequence transparent objects based on distance. If you remove that change, everything works properly.

2. Objects that are not explicitly sequenced by distance (as in part 1 above) are rendered in the order in which they are added to the scene. You can therefore also define rendering order by ensuring that the objects are added to your scene in the order in which you want them rendered. This can work well for static models, such as your first character (if you change it to add the hair after the skin).

3. CC3Node also has a zOrder property, which allows you to override the rendering order explicitly, so that objects with larger zOrder value are rendered before those with smaller zOrder values. This is useful when you have a static model whose components cannot be added in rendering order, or to temporarily override the rendering order of two transparent objects that might be passing in front of each other. Using the zOrder property does depend on using a drawingSequencer that makes use of it (the default drawing sequencer does).

4. Finally, you can temporarily turn off depth testing or masking when rendering particular nodes, by setting the shouldDisableDepthTest and shouldDisableDepthMask properties to YES on those nodes.