Plane.kt

package org.openrndr.extra.meshgenerators

import org.openrndr.draw.VertexBuffer
import org.openrndr.math.Vector2
import org.openrndr.math.Vector3
import org.openrndr.shape.Rectangle

/**
 * Generate a finite plane centered at [center], using the [right], [forward]
 * and [up] vectors for its orientation.
 * [width] and [height] specify the dimensions of the plane.
 * [widthSegments] and [heightSegments] control the plane's number of
 * segments.
 * @return A vertex buffer containing the triangles to render the 3D shape.
 */
fun planeMesh(
    center: Vector3,
    right: Vector3,
    forward: Vector3,
    up: Vector3 = forward.cross(right).normalized,
    width: Double = 1.0,
    height: Double = 1.0,
    widthSegments: Int = 1,
    heightSegments: Int = 1
): VertexBuffer {
    val vertexCount = (widthSegments * heightSegments) * 6
    val vb = meshVertexBuffer(vertexCount)
    vb.put {
        generatePlane(
            center, right, forward, up,
            width, height, widthSegments, heightSegments, bufferWriter(this)
        )
    }
    return vb
}

/**
 * Converts a [Rectangle] to a [VertexBuffer] 2D mesh matching its location and
 * dimensions. [resolution] specifies the size in pixels of the triangles in
 * the mesh.
 * @return A vertex buffer containing the triangles to render the 3D shape.
 */
fun Rectangle.toMesh(
    resolution: Double = 2.0
) = planeMesh(
    center.xy0, Vector3.UNIT_X, Vector3.UNIT_Y, Vector3.UNIT_Z,
    width, height,
    (width / resolution).toInt(),
    (height / resolution).toInt()
)

/**
 * Generates a finite plane with its center at (0,0,0) and spanning the
 * xz-plane.
 * @return A vertex buffer containing the triangles to render the 3D shape.
 */
fun groundPlaneMesh(
    width: Double = 1.0,
    height: Double = 1.0,
    widthSegments: Int = 1,
    heightSegments: Int = 1
) = planeMesh(
    Vector3.ZERO, Vector3.UNIT_X, Vector3.UNIT_Z, Vector3.UNIT_Y,
    width, height, widthSegments, heightSegments
)

/**
 * Generates a finite plane with its center at (0,0,0) and spanning the xy-plane
 * @return A vertex buffer containing the triangles to render the 3D shape.
 */
fun wallPlaneMesh(
    width: Double = 1.0,
    height: Double = 1.0,
    widthSegments: Int = 1,
    heightSegments: Int = 1
) = planeMesh(
    Vector3.ZERO, Vector3.UNIT_X, Vector3.UNIT_Y, Vector3.UNIT_Z,
    width, height, widthSegments, heightSegments
)

/**
 * Generate plane centered at [center], using the [right], [forward] and [up]
 * vectors for its orientation.
 * [width] and [height] specify the dimensions of the plane.
 * [widthSegments] and [heightSegments] control the plane's number of
 * segments.
 *
 * @param writer the vertex writer function
 */
fun generatePlane(
    center: Vector3,
    right: Vector3,
    forward: Vector3,
    up: Vector3 = forward.cross(right).normalized,
    width: Double = 1.0,
    height: Double = 1.0,
    widthSegments: Int = 1,
    heightSegments: Int = 1,
    writer: VertexWriter
) {

    val forwardStep = forward.normalized * (height / heightSegments)
    val rightStep = right.normalized * (width / widthSegments)

    val corner = center -
            forward.normalized * (height * 0.5) -
            right.normalized * (width * 0.5)

    val step = Vector2(1.0 / widthSegments, 1.0 / heightSegments)

    for (v in 0 until heightSegments) {
        for (u in 0 until widthSegments) {

            val uv00 = Vector2(u + 0.0, v + 0.0) * step
            val uv01 = Vector2(u + 0.0, v + 1.0) * step
            val uv10 = Vector2(u + 1.0, v + 0.0) * step
            val uv11 = Vector2(u + 1.0, v + 1.0) * step

            val c00 = corner +
                    forwardStep * v.toDouble() + rightStep * u.toDouble()
            val c01 = corner +
                    forwardStep * (v + 1).toDouble() + rightStep * u.toDouble()
            val c10 = corner +
                    forwardStep * v.toDouble() + rightStep * (u + 1).toDouble()
            val c11 = corner +
                    forwardStep * (v + 1).toDouble() + rightStep * (u + 1).toDouble()

            writer(c11, up, uv00)
            writer(c10, up, uv10)
            writer(c00, up, uv11)

            writer(c00, up, uv11)
            writer(c01, up, uv01)
            writer(c11, up, uv00)
        }
    }
}