Tetra3D

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What is Tetra3D?

Tetra3D is a 3D hybrid software / hardware renderer written in Go by means of Ebitengine, primarily for video games. Compared to a professional 3D rendering system like OpenGL or Vulkan, it's slow(er), but it's also janky, and I love it for that. Tetra3D is largely implemented in software, but uses the GPU a bit for rendering the triangles and for performing inter-object depth testing (by use of Kage shaders to compare and write depth and composite the result onto the finished texture). Depth testing can be turned off for a slight performance increase in exchange for no visual inter-object intersection.

Tetra3D's rendering evokes a similar feeling to primitive 3D game consoles like the PS1, N64, or DS. Being that a largely-software renderer is not nearly fast enough for big, modern 3D titles, the best you're going to get out of Tetra is drawing some 3D elements for your primarily 2D Ebitengine game, or a relatively simple fully 3D game (i.e. something on the level of a PS1, or N64 game). That said, limitation breeds creativity, and I am intrigued at the thought of what people could make with Tetra.

Tetra3D also gives you a Blender add-on to make the Blender > Tetra3D development process flow a bit smoother. See the Releases section for the add-on, and this wiki page for more information.

Why did I make it?

Because there's not really too much of an ability to do 3D for gamedev in Go apart from g3n, go-gl and Raylib-go. I like Go, I like janky 3D, and so, here we are.

It's also interesting to have the ability to spontaneously do things in 3D sometimes. For example, if you were making a 2D game with Ebitengine but wanted to display just a few GUI elements or objects in 3D, Tetra3D should work well for you.

Finally, while this hybrid renderer is not by any means fast, it is relatively simple and easy to use. Any platforms that Ebiten supports should also work for Tetra3D automatically. Basing a 3D framework off of an existing 2D framework also means any improvements or refinements to Ebitengine may be of help to Tetra3D, and it keeps the codebase small and unified between platforms.

Why Tetra3D? Why is it named that?

Because it's like a tetrahedron, a relatively primitive (but visually interesting) 3D shape made of 4 triangles. Otherwise, I had other names, but I didn't really like them very much. "Jank3D" was the second-best one, haha.

How do you get it?

go get github.com/solarlune/tetra3d

Tetra depends on Ebitengine itself for rendering. Tetra3D requires Go v1.18 or above. This minimum required version is somewhat arbitrary, as it could run on an older Go version if a couple of functions (primarily the ones that loads data from a file directly) were changed.

There is an optional Blender add-on as well (tetra3d.py) that can be downloaded from the releases page or from the repo directly (i.e. click on the file and download it). The add-on provides some useful helper functionality that makes using Tetra3D simpler - for more information, check the Wiki.

How do you use it?

Load a scene, render it. A simple 3D framework means a simple 3D API.

Here's an example:

package main

import (
	"errors"
	"fmt"
	"image/color"

	"github.com/solarlune/tetra3d"
	"github.com/hajimehoshi/ebiten/v2"
)

type Game struct {
	GameScene    *tetra3d.Scene
	Camera       *tetra3d.Camera
}

func NewGame() *Game {

	g := &Game{}

	// First, we load a scene from a .gltf or .glb file. LoadGLTFFile takes a filepath and
	// any loading options (nil can be taken as a valid default set of loading options), and 
	// returns a *tetra3d.Library and an error if it was unsuccessful. We can also use 
	// tetra3d.LoadGLTFData() if we don't have access to the host OS's filesystem (if the 
	// assets are embedded, for example).

	library, err := tetra3d.LoadGLTFFile("example.gltf", nil) 

	if err != nil {
		panic(err)
	}

	// A Library is essentially everything that got exported from your 3D modeler - 
	// all of the scenes, meshes, materials, and animations. The ExportedScene of a Library
	// is the scene that was active when the file was exported.

	// We'll clone the ExportedScene so we don't change it irreversibly; making a clone
	// of a Tetra3D resource (Scene, Node, Material, Mesh, Camera, whatever) makes a deep 
	// copy of it.
	g.GameScene = library.ExportedScene.Clone()

	// Tetra3D uses OpenGL's coordinate system (+X = Right, +Y = Up, +Z = Backward [towards the camera]), 
	// in comparison to Blender's coordinate system (+X = Right, +Y = Forward, 
	// +Z = Up). Note that when loading models in via GLTF or DAE, models are
	// converted automatically (so up is +Z in Blender and +Y in Tetra3D automatically).

	// We could create a new Camera as below - we would pass the size of the screen to the 
	// Camera so it can create its own buffer textures (which are *ebiten.Images).

	// g.Camera = tetra3d.NewCamera(ScreenWidth, ScreenHeight)

	// However, we can also just grab an existing camera from the scene if it 
	// were exported from the GLTF file - if exported through Blender's Tetra3D add-on,
	// then the camera size can be easily set from within Blender.

	g.Camera = g.GameScene.Root.Get("Camera").(*tetra3d.Camera)

	// Camera implements the tetra3d.INode interface, which means it can be placed
	// in 3D space and can be parented to another Node somewhere in the scene tree.
	// Models, Lights, and Nodes (which are essentially "empties" one can
	// use for positioning and parenting) can, as well.

	// We can place Models, Cameras, and other Nodes with node.SetWorldPosition() or 
	// node.SetLocalPosition(). There are also variants that take a 3D Vector.

	// The *World variants of positioning functions takes into account absolute space; 
	// the Local variants position Nodes relative to their parents' positioning and 
	// transforms (and is more performant.)
	// You can also move Nodes using Node.Move(x, y, z) / Node.MoveVec(vector).

	// Each Scene has a tree that starts with the Root Node. To add Nodes to the Scene, 
	// parent them to the Scene's base, like so:

	// scene.Root.AddChildren(object)

	// To remove them, you can unparent them from either the parent (Node.RemoveChildren())
	// or the child (Node.Unparent()). When a Node is unparented, it is removed from the scene
	// tree; if you want to destroy the Node, then dropping any references to this Node 
	// at this point would be sufficient.

	// For Cameras, we don't actually need to place them in a scene to view the Scene, since
	// the presence of the Camera in the Scene node tree doesn't impact what it would see.

	// We can see the tree "visually" by printing out the hierarchy:
	fmt.Println(g.GameScene.Root.HierarchyAsString())

	// You can also visualize the scene hierarchy using TetraTerm:
	// https://github.com/SolarLune/tetraterm

	return g
}

func (g *Game) Update() error { return nil }

func (g *Game) Draw(screen *ebiten.Image) {

	// Here, we'll call Camera.Clear() to clear its internal backing texture. This
	// should be called once per frame before drawing your Scene.
	g.Camera.Clear()

	// Now we'll render the Scene from the camera. The Camera's ColorTexture will then 
	// hold the result. 

	// Camera.RenderScene() renders all Nodes in a scene, starting with the 
	// scene's root. You can also use Camera.Render() to simply render a selection of
	// individual Models, or Camera.RenderNodes() to render a subset of a scene tree.
	g.Camera.RenderScene(g.GameScene) 

	// To see the result, we draw the Camera's ColorTexture to the screen. 
	// Before doing so, we'll clear the screen first. In this case, we'll do this 
	// with a color, though we can also go with screen.Clear().
	screen.Fill(color.RGBA{20, 30, 40, 255})

	// Draw the resulting texture to the screen, and you're done! You can 
	// also visualize the depth texture with g.Camera.DepthTexture().
	screen.DrawImage(g.Camera.ColorTexture(), nil) 

	// Note that the resulting texture is indeed just an ordinary *ebiten.Image, so 
	// you can also use this as a texture for a Model's Material, as an example.

}

func (g *Game) Layout(w, h int) (int, int) {
	
	// Here, by simply returning the camera's size, we are essentially
	// scaling the camera's output to the window size and letterboxing as necessary. 

	// If you wanted to extend the camera according to window size, you would 
	// have to resize the camera using the window's new width and height.
	return g.Camera.Size()

}

func main() {

	game := NewGame()

	if err := ebiten.RunGame(game); err != nil {
		panic(err)
	}

}

You can also do collision testing between BoundingObjects, a category of nodes designed for checking against collisions. As a simplified example:

type Game struct {

	Cube *tetra3d.BoundingAABB
	Capsule *tetra3d.BoundingCapsule

}

func NewGame() *Game {

	g := &Game{}

	// Create a new BoundingCapsule named "player", 1 unit tall with a 
	// 0.25 unit radius for the caps at the ends.
	g.Capsule = tetra3d.NewBoundingCapsule("player", 1, 0.25)

	// Create a new BoundingAABB named "block", of 0.5 width, height, 
	// and depth (in that order).
	g.Cube = tetra3d.NewBoundingAABB("block", 0.5, 0.5, 0.5)

	// Move the cube over on the X axis by 4 units.
	g.Cube.Move(-4, 0, 0)

	return g

}

func (g *Game) Update() {

	// Move the capsule 0.2 units to the right every frame.
	g.Capsule.Move(0.2, 0, 0)

	// Will print the result of the Collision, or nil, if there was no intersection.
	fmt.Println(g.Capsule.Collision(g.Cube))

}

If you wanted a deeper collision test with multiple objects, you can do so using IBoundingObject.CollisionTest(). Take a look at the Wiki and the bounds example for more info.

That's basically it. Feel free to examine all of the examples in the examples folder. Calling go run . from within their directories will run them - the mouse usually controls the view, and clicking locks and unlocks the view. You can also view the examples online here.

There's a quick start project repo available here, as well to help with getting started.

For more information, check out the Wiki for tips and tricks.

What's missing?

The following is a rough to-do list (tasks with checks have been implemented):

Collision Type	Sphere	AABB	Triangle	Capsule
Sphere	✅	✅	✅	✅
AABB	✅	✅	⛔	✅
Triangle	✅	⛔	⛔	✅
Capsule	✅	✅	✅	⛔
Ray	✅	✅	✅	✅

✅ = Fully supported, should be working without issues ⛔ = Partially supported; somewhat buggy

Again, it's incomplete and jank. However, it's also pretty cool!

Shout-out time~

Huge shout-out to the open-source community:

StackOverflow, in general, FOR REAL - this would've been impossible otherwise
quartercastle's vector package
fauxgl
tinyrenderer
learnopengl.com
3DCollisions
Simon Rodriguez's "Writing a Small Software Renderer" article
And many other articles that I've forgotten to note down

... For sharing the information and code to make this possible; I would definitely have never been able to create this otherwise.

SolarLune/tetra3d