[orx-mesh, orx-mesh-generator, orx-obj-loader] Add decal and tangent tools

orx-mesh/src/commonMain/kotlin/IndexedPolygonExtensions.kt

@@ -0,0 +1,33 @@
+package org.openrndr.extra.mesh
+
+import org.openrndr.math.LinearType
+import org.openrndr.math.Vector3
+
+internal fun <T : LinearType<T>> bc(barycentric: Vector3, items: List<T>): T {
+    return (items[0] * barycentric.x) + (items[1] * barycentric.y) + (items[2] * barycentric.z)
+}
+
+/**
+ * Evaluate a point in triangle
+ * @param vertexData the vertex data to use
+ * @param barycentric the barycentric coordinates of the point to evaluate
+ */
+fun IIndexedPolygon.point(vertexData: VertexData, barycentric: Vector3): Point {
+    require(positions.size == 3)
+
+    val positions = vertexData.positions.slice(positions)
+    val colors = vertexData.colors.slice(colors)
+    val normals = vertexData.normals.slice(normals)
+    val tangents = vertexData.tangents.slice(tangents)
+    val bitangents = vertexData.bitangents.slice(bitangents)
+    val textureCoords = vertexData.textureCoords.slice(textureCoords)
+
+    return Point(
+        (if (positions.isNotEmpty()) bc(barycentric, positions) else null)!!,
+        if (textureCoords.isNotEmpty()) bc(barycentric, textureCoords) else null,
+        if (colors.isNotEmpty()) bc(barycentric, colors) else null,
+        if (normals.isNotEmpty()) bc(barycentric, normals) else null,
+        if (tangents.isNotEmpty()) bc(barycentric, tangents) else null,
+        if (bitangents.isNotEmpty()) bc(barycentric, bitangents) else null
+    )
+}