Image by author — The outside texture is from https://en.wikipedia.org/wiki/File:Blue_Marble_2002.png, and the inside texture is from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

We have written about three.js fundamentals, 3D modeling, color textures, and environment textures via reflection and refraction.

In this article, we are going to apply textures outside and inside 3D objects, and explore examples to travel in and out of 3D objects.

We reused the Create React App working environment in the previous article, installed with the following packages:

• three.js (three): It is a 3D JavaScript library that renders 3D content on a webpage. It aims to create an easy-to-use, lightweight, cross-browser, general-purpose 3D library.
• react-three-fiber (@react-three/fiber): It is a React renderer for three.js. It allows us to write three.js using JSX, which is more declarative. The React wrapper also handles a lot of things behind the scene, such as canvas resizing and disposing of unmounted objects.
• @react-three/drei: It is a collection of useful helpers for rendering react-three-fiber. It makes it easier to use many types of objects, such as cameras, controls, images, shapes, 3D models, environments, etc.

Step by step, we travel in and out of 3D objects with the following examples:

Look at the Cube From Outside

In three.js, texture is created by applying an image to a surface, or as a reflection or refraction map. A cube needs six images to construct the textures of the six faces. These images are specified in the following order: pos-x, neg-x, pos-y, neg-y, pos-z, and neg-z.

We use the image of a mustard field.

Image by author

Split it into four files, and name them mustard1.jpg, mustard2.jpg, mustard3.jpg, and mustard4.jpg. Put them under the public/textures folder.

Image by author

Here is public/sky.jpg:

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Here is public/grass.jpg:

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These DIY images are not perfect, but they are good enough to prove the concept.

Similar to examples in the texture article, we look at the cube from the outside using the following src/App.js:

We have explained in detail what three.js is and how it works in React. A mesh is a type of object that is triangular polygon mesh based. It is the skeleton that makes up the figure of 3D objects. It is defined by geometry (shape), material (surface), and scene (placement).

• In the above code, the texture images are loaded at lines 7–14. Each texture is set to the map prop of meshBasicMaterial (line 31).
• the Box component (lines 6–37) calls useFrame to perform rotation (lines 16–22). It defines a mesh (lines 25–35), which includes a box/cube (line 26) with width, height, and depth defined as [3, 3, 3].
• The materials (lines 27–34) are configured with meshBasicMaterial, a material for drawing geometries that are not affected by lights. At line 32, the material side is set to THREE.FrontSide.
• Box is displayed on Canvas (lines 41–48), which renders three’s components. Canvas sets the camera’s props to be { fov: 70, near: 0.01, far: 100, position: [0, 0, 6] } (line 42), and it occupies the whole viewport with a sky-blue background (line 43).
• Execute npm start. We watch at the camera position at [0, 0, 6], outside of the box.

Image by auther

Look at the Cube From Inside

Step inside the cube is easy — simply move the camera position inside of the box.

Here is src/App.js:

• At line 32, the material side is set to THREE.BackSide.
• At line 42, the camera is located at [0, 0, 1].
• Execute npm start. We watch at the camera position at [0, 0, 1], inside of the box.

Image by author

Travel in and out of the Cube

We can look at the cube from the outside and inside. It allows us to travel in and out of the cube. Two things are needed to achieve it:

• Move the camera around in and out of the cube.
• Make the material both sided.

Here is src/App.js:

• In useFrame (lines 17–34), the camera moves in each invocation. It moves from the inside of the cube to the outside. If it is too far back (z is beyond 8 at line 23), it moves forward and travels in the cube. If it is too close (z reaches 1 at line 25), it moves backward and travels out of the cube. This movement is repeated.
• At line 44, the material side is set to THREE.DoubleSide.
• Execute npm start. We travel in and out of the cube.

Image by author

Look at the Sphere From Outside

We have projected a reflect/refract map on the surface of a sphere. Here, we apply an image directly to the sphere surface.

Since the sphere surface is not flat, an equirectangular map is needed. The equirectangular map is a 2D image that projects a curved surface of a globe on a plane.

The following equirectangular image is downloaded from Wikipedia, and it is placed under the public/textures folder as map.jpeg.

Image from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

Here is src/App.js:

• At line 6, the equirectangular map is loaded for the texture, which is set to the map prop of meshBasicMaterial (line 20).
• The Sphere component (lines 5–23) calls useFrame to perform rotation (lines 9–15). It defines a mesh (lines 18–21), which includes a sphere (line 19) with radius, widthSegments, and heightSegments defined as [3, 64, 32].
• The material (line 20) is configured with meshBasicMaterial, where side is set to THREE.FrontSide.
• Sphere is displayed on Canvas (lines 27–34), which renders three’s components. Canvas sets the camera’s props to be { fov: 70, near: 0.01, far: 100, position: [0, 0, 6] } (line 28), and it occupies the whole viewport with a light sky blue background (line 29).
• Execute npm start. We watch the camera position at [0, 0, 6], outside of the sphere.

Image by author — The texture is from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

Look at the Sphere From Inside

Travel inside the sphere by moving the camera position.

Here is src/App.js:

• At line 20, the material side is set to THREE.BackSide.
• At line 28, the camera is located at [0, 0, 1].
• Execute npm start. We watch the camera position at [0, 0, 1], inside of the sphere.

Image by author — The texture is from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

Travel in and out of the Sphere

Similar to the cube, we can travel in and out of the sphere. All we need to do is to move the camera around and make the material both sided.

Here is src/App.js:

• In useFrame (lines 9–26), the camera moves in each invocation. It moves from inside of the sphere to outside. If it is too far back (z is beyond 8 at line 23), it moves forward and travels in the sphere. If it is too close (z reaches 1 at line 25), it moves backward and travels out of the sphere. This movement is repeated.
• At line 44, the material side is set to THREE.DoubleSide.
• Execute npm start. We travel in and out of the sphere.

Image by author — The texture is from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

A Sphere With Different Textures on Both Sides

We have put color map at the frontside, backside, and both sides. How can we show different textures for the frontside and backside?

In order to do that, we need to create two objects — one shows the frontside and the other one shows the backside.

We use the sphere to illustrate how it is achieved. First, download the equirectangular image for the other side, and place it under the public/textures folder as map2.png.

Image from https://en.wikipedia.org/wiki/File:Blue_Marble_2002.png

Here is src/App.js:

• At lines 5–34, the Sphere component takes two props, mapName and side.
• At line 43, the first Sphere is placed in Canvas with textures/map2.png for the frontside.
• At line 44, the second Sphere is placed in Canvas with textures/map.jpeg for the backside.
• Execute npm start. We travel in and out of the sphere with different textures on both sides.

Image by author — The outside texture is from https://en.wikipedia.org/wiki/File:Blue_Marble_2002.png, and the inside texture is from https://en.wikipedia.org/wiki/File:Equirectangular_projection_SW.jpg

Conclusion

We have shown code examples to look at textures from outside and inside 3D objects. It is also possible to apply different textures to outside and inside 3D objects. By moving the camera, we can travel in and out of the 3D objects.

Thanks for reading. I hope this was helpful. If you are interested, check out my other Medium articles.

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