Cube.kt

package io.github.sceneview.mesh

import com.google.android.filament.Engine
import io.github.sceneview.math.Direction
import io.github.sceneview.math.Position
import io.github.sceneview.math.Size

/**
 * Creates a [Geometry] in the shape of a cube with the give specifications.
 *
 * @param size the size of the constructed cube
 * @param center the center of the constructed cube
 */
class Cube(engine: Engine, size: Size, center: Position) : Geometry(
    engine = engine,
    vertices = mutableListOf<Vertex>().apply {
        val extents = size * 0.5f
        val p0 = center + Size(-extents.x, -extents.y, extents.z)
        val p1 = center + Size(extents.x, -extents.y, extents.z)
        val p2 = center + Size(extents.x, -extents.y, -extents.z)
        val p3 = center + Size(-extents.x, -extents.y, -extents.z)
        val p4 = center + Size(-extents.x, extents.y, extents.z)
        val p5 = center + Size(extents.x, extents.y, extents.z)
        val p6 = center + Size(extents.x, extents.y, -extents.z)
        val p7 = center + Size(-extents.x, extents.y, -extents.z)
        val up = Direction(y = 1.0f)
        val down = Direction(y = -1.0f)
        val front = Direction(z = -1.0f)
        val back = Direction(z = 1.0f)
        val left = Direction(x = -1.0f)
        val right = Direction(x = 1.0f)
        val uv00 = UvCoordinate(x = 0.0f, y = 0.0f)
        val uv10 = UvCoordinate(x = 1.0f, y = 0.0f)
        val uv01 = UvCoordinate(x = 0.0f, y = 1.0f)
        val uv11 = UvCoordinate(x = 1.0f, y = 1.0f)
        // Bottom
        addAll(
            listOf(
                Vertex(position = p0, normal = down, uvCoordinate = uv01),
                Vertex(position = p1, normal = down, uvCoordinate = uv11),
                Vertex(position = p2, normal = down, uvCoordinate = uv10),
                Vertex(position = p3, normal = down, uvCoordinate = uv00),
                // Left
                Vertex(position = p7, normal = left, uvCoordinate = uv01),
                Vertex(position = p4, normal = left, uvCoordinate = uv11),
                Vertex(position = p0, normal = left, uvCoordinate = uv10),
                Vertex(position = p3, normal = left, uvCoordinate = uv00),
                // Back
                Vertex(position = p4, normal = back, uvCoordinate = uv01),
                Vertex(position = p5, normal = back, uvCoordinate = uv11),
                Vertex(position = p1, normal = back, uvCoordinate = uv10),
                Vertex(position = p0, normal = back, uvCoordinate = uv00),
                // Front
                Vertex(position = p6, normal = front, uvCoordinate = uv01),
                Vertex(position = p7, normal = front, uvCoordinate = uv11),
                Vertex(position = p3, normal = front, uvCoordinate = uv10),
                Vertex(position = p2, normal = front, uvCoordinate = uv00),
                // Right
                Vertex(position = p5, normal = right, uvCoordinate = uv01),
                Vertex(position = p6, normal = right, uvCoordinate = uv11),
                Vertex(position = p2, normal = right, uvCoordinate = uv10),
                Vertex(position = p1, normal = right, uvCoordinate = uv00),
                // Top
                Vertex(position = p7, normal = up, uvCoordinate = uv01),
                Vertex(position = p6, normal = up, uvCoordinate = uv11),
                Vertex(position = p5, normal = up, uvCoordinate = uv10),
                Vertex(position = p4, normal = up, uvCoordinate = uv00)
            )
        )
    },
    submeshes = mutableListOf<Submesh>().apply {
        val sideCount = 6
        val verticesPerSide = 4
        for (i in 0 until sideCount) {
            add(
                Submesh(
                    // First triangle for this side.
                    3 + verticesPerSide * i,
                    1 + verticesPerSide * i,
                    0 + verticesPerSide * i,
                    // Second triangle for this side.
                    3 + verticesPerSide * i,
                    2 + verticesPerSide * i,
                    1 + verticesPerSide * i
                )
            )
        }
    })