ArtifactForms/MeshLibCore

package mesh.modifier;

import math.Vector3f;
import mesh.Mesh3D;

/**
 * A modifier that applies a shear transformation to a 3D mesh. The shear effect
 * distorts the mesh along a specified axis, creating a slanted or skewed
 * appearance.
 * 
 * The transformation is applied to each vertex of the mesh based on the
 * specified shear axis and factor.
 */
public class ShearModifier implements IMeshModifier {

    /**
     * Represents the axis and plane along which the shear is applied.
     * 
     * <pre>
     * - XY: Shear along the X-axis based on the Y-coordinate.
     * - XZ: Shear along the X-axis based on the Z-coordinate.
     * - YX: Shear along the Y-axis based on the X-coordinate.
     * - YZ: Shear along the Y-axis based on the Z-coordinate.
     * - ZX: Shear along the Z-axis based on the X-coordinate.
     * - ZY: Shear along the Z-axis based on the Y-coordinate.
     * </pre>
     */
    public enum ShearAxis {
        XY, XZ, YX, YZ, ZX, ZY
    }

    /**
     * The factor by which the mesh is sheared.
     */
    private float shearFactor;

    /**
     * The axis along which the shear transformation is applied.
     */
    private ShearAxis axis;

    /**
     * Constructs a ShearModifier with the specified shear axis and factor.
     * 
     * @param axis        the axis along which the shear transformation is applied
     * @param shearFactor the factor by which the mesh is sheared
     * @throws IllegalArgumentException if axis is null
     */
    public ShearModifier(ShearAxis axis, float shearFactor) {
        if (axis == null) {
            throw new IllegalArgumentException("Shear axis cannot be null.");
        }
        this.axis = axis;
        this.shearFactor = shearFactor;
    }

    /**
     * Applies the shear transformation to the given mesh.
     * 
     * @param mesh the mesh to be modified
     * @return the modified mesh with the shear transformation applied
     */
    @Override
    public Mesh3D modify(Mesh3D mesh) {
        validateMesh(mesh);
        if (mesh.vertices.isEmpty()) {
            return mesh;
        }
        applyShear(mesh);
        return mesh;
    }

    /**
     * Applies the shear transformation to all vertices in the given mesh.
     * 
     * This method uses a parallel stream to process the vertices, applying the
     * shear transformation in a concurrent manner for improved performance on
     * large meshes. The shear transformation is determined by the specified shear
     * axis and factor.
     * 
     * @param mesh the mesh whose vertices will be sheared
     * @throws IllegalArgumentException if the mesh is null or contains null
     *                                  vertices
     */
    private void applyShear(Mesh3D mesh) {
        mesh.vertices.parallelStream().forEach(this::applyShearToVertex);
    }

    /**
     * Applies the shear transformation to a single vertex based on the specified
     * shear axis and factor.
     * 
     * @param vertex the vertex to modify
     */
    private void applyShearToVertex(Vector3f vertex) {
        switch (axis) {
        case XY -> vertex.x += shearFactor * vertex.y;
        case XZ -> vertex.x += shearFactor * vertex.z;
        case YX -> vertex.y += shearFactor * vertex.x;
        case YZ -> vertex.y += shearFactor * vertex.z;
        case ZX -> vertex.z += shearFactor * vertex.x;
        case ZY -> vertex.z += shearFactor * vertex.y;
        default ->
          throw new IllegalArgumentException("Unsupported shear axis: " + axis);
        }
    }

    /**
     * Validates that the mesh is not null.
     *
     * @param mesh the mesh to validate.
     * @throws IllegalArgumentException if the mesh is null.
     */
    private void validateMesh(Mesh3D mesh) {
        if (mesh == null) {
            throw new IllegalArgumentException("Mesh cannot be null.");
        }
    }

    /**
     * Gets the current shear axis.
     * 
     * @return the shear axis
     */
    public ShearAxis getAxis() {
        return axis;
    }

    /**
     * Sets the shear axis.
     * 
     * @param axis the shear axis to set
     */
    public void setAxis(ShearAxis axis) {
        if (axis == null) {
            throw new IllegalArgumentException("Shear axis cannot be null.");
        }
        this.axis = axis;
    }

    /**
     * Gets the current shear factor.
     * 
     * @return the shear factor
     */
    public float getShearFactor() {
        return shearFactor;
    }

    /**
     * Sets the shear factor.
     * 
     * @param shearFactor the shear factor to set
     */
    public void setShearFactor(float shearFactor) {
        this.shearFactor = shearFactor;
    }

}