package com.exh.bevel;

import com.exh.math.primitive.Geo;
import com.exh.math.primitive.Point3;
import com.exh.math.primitive.Quad;

public class SurfaceShader {

	public final static class Params {
		public double			mZ = 0;
		public final Point3	mN = new Point3();
	}
	
	private final double[]		mX = new double[2];	// 0 = left, 1 = right
	private final double[]		mZ = new double[2];
	private final Point3[]		mN = Point3.newArray(2);
		
	private final Point3		mA = new Point3(),
								mB = new Point3(),
								mOut = new Point3();

	// Call setTo() with a Y value first.
	void getAt(final double x, final Params p) {
		final double		pos = (x-mX[0]) / (mX[1]-mX[0]);
		p.mZ = (mZ[0] * (1-pos)) + (mZ[1] * pos);
		p.mN.x = (mN[0].x * (1-pos)) + (mN[1].x * pos);
		p.mN.y = (mN[0].y * (1-pos)) + (mN[1].y * pos);
		p.mN.z = (mN[0].z * (1-pos)) + (mN[1].z * pos);
	}

	void setTo(final Surface s, final double y) {
		mA.y = mB.y = y;
		mA.x = s.mL-1;
		mB.x = s.mR+1;

		mZ[0] = 0;
		mZ[1] = 0;
		mX[0] = 1000000;
		mX[1] = -1000000;
		
		double				minY = 0, maxY = 0;
		int					minK = -1, maxK = -1;
		Point3				prev = s.mQ.mPt[Quad.SIZE-1];
		final boolean		isTri = s.mQ.mPt[1].sameAs(s.mQ.mPt[2]);
		for (int k=0; k<Quad.SIZE; k++) {
			final Point3	next = s.mQ.mPt[k];
			// Handle the case where the quad is really a tri by skipping
			// one of the interior points.
			if (!(isTri && k == 2)) {
				if (Geo.lineSegmentIntersection(mA, mB, prev, next, mOut)) {
					if (mOut.x < mX[0]) {
						mX[0] = mOut.x;
						minY = mOut.y;
						minK = k;
					}
					if (mOut.x > mX[1]) {
						mX[1] = mOut.x;
						maxY = mOut.y;
						maxK = k;
					}
				}
			}
			prev = next;
		}
		if (minK < 0) {
			System.out.println("Error in shader y=" + y + " q=" + s.mQ);
			return;
		}
		// Interpolate the left and right sides
		fill(s, minK, minY, 0);
		fill(s, maxK, maxY, 1);
	}
	
	private final void fill(final Surface s, final int idx, final double y,
							final int dst) {
		final int		pidx = (idx <= 0 ? Quad.SIZE-1 : idx-1);
		Point3			prev = s.mQ.mPt[pidx];
		Point3			next = s.mQ.mPt[idx];
		final double	segD = Geo.dist(prev.x, prev.y, next.x, next.y),
						ptD = Geo.dist(prev.x, prev.y, mX[dst], y);
		final double	pos = ptD / segD;
		// Depth
		mZ[dst] = ((prev.z * (1-pos)) + (next.z * pos));
		// Normal
		prev = s.mPtNormal[pidx];
		next = s.mPtNormal[idx];
		mN[dst].x = ((prev.x * (1-pos)) + (next.x * pos));
		mN[dst].y = ((prev.y * (1-pos)) + (next.y * pos));
		mN[dst].z = ((prev.z * (1-pos)) + (next.z * pos));
	}
}