SabinT · March 25, 2024 06:29
diff --git a/Homography.cs b/Homography.cs

 using UnityEngine;

 /// <summary>
 /// Utility to map points inside a unit square (0,0)-(1,1) to a quad defined by 4 points.
 /// Uses math from:
 /// https://github.com/hecomi/uHomography/blob/master/Assets/uHomography/Runtime/Scripts/Homography.cs
 /// Instructions to use for projection mapping:
 /// * Gather screen coordinates of four corner points, and call UpdateMatrix with them.
 /// * The Transform method now will map a point inside a unit square to an appropriate point on the screen quad.
 /// * Create a subdivided quad with both coordinates and uvs from (0,0)-(1,1)
 /// * Use the Transform method to get new coordinates, but keep the UVs the same.
 /// Hecomi's github contains a shader based implementation (no need to subdivide) if you want to investigate that further.
 /// </summary>
 public class Homography
 {
    private readonly float[] _matrix = new float[9];

    public Vector2 Transform(Vector2 pos)
    {
        if (_matrix == null)
        {
            return pos;
        }

        float s = _matrix[6] * pos.x + _matrix[7] * pos.y + _matrix[8];
        float x = (_matrix[0] * pos.x + _matrix[1] * pos.y + _matrix[2]) / s;
        float y = (_matrix[3] * pos.x + _matrix[4] * pos.y + _matrix[5]) / s;
        return new Vector2(x, y);
    }

    public void UpdateMatrix(Vector2 topLeft, Vector2 topRight, Vector2 bottomLeft, Vector2 bottomRight)
    {
        Vector2 p00 = bottomLeft;
        Vector2 p01 = bottomRight;
        Vector2 p10 = topLeft;
        Vector2 p11 = topRight;

        var x00 = p00.x;
        var y00 = p00.y;
        var x01 = p01.x;
        var y01 = p01.y;
        var x10 = p10.x;
        var y10 = p10.y;
        var x11 = p11.x;
        var y11 = p11.y;

        var a = x10 - x11;
        var b = x01 - x11;
        var c = x00 - x01 - x10 + x11;
        var d = y10 - y11;
        var e = y01 - y11;
        var f = y00 - y01 - y10 + y11;

        var h13 = x00;
        var h23 = y00;
        var h32 = (c * d - a * f) / (b * d - a * e);
        var h31 = (c * e - b * f) / (a * e - b * d);
        var h11 = x10 - x00 + h31 * x10;
        var h12 = x01 - x00 + h32 * x01;
        var h21 = y10 - y00 + h31 * y10;
        var h22 = y01 - y00 + h32 * y01;

        // Update existing array
        _matrix[0] = h11;
        _matrix[1] = h12;
        _matrix[2] = h13;
        _matrix[3] = h21;
        _matrix[4] = h22;
        _matrix[5] = h23;
        _matrix[6] = h31;
        _matrix[7] = h32;
        _matrix[8] = 1f;
    }
 }

	using UnityEngine;

	/// <summary>
	/// Utility to map points inside a unit square (0,0)-(1,1) to a quad defined by 4 points.
	/// Uses math from:
	/// https://github.com/hecomi/uHomography/blob/master/Assets/uHomography/Runtime/Scripts/Homography.cs
	/// Instructions to use for projection mapping:
	/// * Gather screen coordinates of four corner points, and call UpdateMatrix with them.
	/// * The Transform method now will map a point inside a unit square to an appropriate point on the screen quad.
	/// * Create a subdivided quad with both coordinates and uvs from (0,0)-(1,1)
	/// * Use the Transform method to get new coordinates, but keep the UVs the same.
	/// Hecomi's github contains a shader based implementation (no need to subdivide) if you want to investigate that further.
	/// </summary>
	public class Homography
	{
	private readonly float[] _matrix = new float[9];

	public Vector2 Transform(Vector2 pos)
	{
	if (_matrix == null)
	{
	return pos;
	}

	float s = _matrix[6] * pos.x + _matrix[7] * pos.y + _matrix[8];
	float x = (_matrix[0] * pos.x + _matrix[1] * pos.y + _matrix[2]) / s;
	float y = (_matrix[3] * pos.x + _matrix[4] * pos.y + _matrix[5]) / s;
	return new Vector2(x, y);
	}

	public void UpdateMatrix(Vector2 topLeft, Vector2 topRight, Vector2 bottomLeft, Vector2 bottomRight)
	{
	Vector2 p00 = bottomLeft;
	Vector2 p01 = bottomRight;
	Vector2 p10 = topLeft;
	Vector2 p11 = topRight;

	var x00 = p00.x;
	var y00 = p00.y;
	var x01 = p01.x;
	var y01 = p01.y;
	var x10 = p10.x;
	var y10 = p10.y;
	var x11 = p11.x;
	var y11 = p11.y;

	var a = x10 - x11;
	var b = x01 - x11;
	var c = x00 - x01 - x10 + x11;
	var d = y10 - y11;
	var e = y01 - y11;
	var f = y00 - y01 - y10 + y11;

	var h13 = x00;
	var h23 = y00;
	var h32 = (c * d - a * f) / (b * d - a * e);
	var h31 = (c * e - b * f) / (a * e - b * d);
	var h11 = x10 - x00 + h31 * x10;
	var h12 = x01 - x00 + h32 * x01;
	var h21 = y10 - y00 + h31 * y10;
	var h22 = y01 - y00 + h32 * y01;

	// Update existing array
	_matrix[0] = h11;
	_matrix[1] = h12;
	_matrix[2] = h13;
	_matrix[3] = h21;
	_matrix[4] = h22;
	_matrix[5] = h23;
	_matrix[6] = h31;
	_matrix[7] = h32;
	_matrix[8] = 1f;
	}
	}