AutoExpandGridLayoutGroup

/// <summary>
/// AutoExpandGridLayoutGroup a variation of Unity's Grid Layout Group.
/// It sorts children under a panel into dynamic grid layout.
/// Also resizes children inside panel according to panel size and child count.
/// Helps taken from https://forum.unity.com/threads/solved-how-to-make-grid-layout-group-cell-size-x-auto-expand.448534/
/// </summary>
using UnityEngine;
using System.Collections.Generic;

namespace UnityEngine.UI
{
    [AddComponentMenu("Layout/Auto Expand Grid Layout Group", 152)]
    public class AutoExpandGridLayoutGroup : LayoutGroup
    {
        public enum Corner { UpperLeft = 0, UpperRight = 1, LowerLeft = 2, LowerRight = 3 }
        public enum Axis { Horizontal = 0, Vertical = 1 }
        public enum Constraint { Flexible = 0, FixedColumnCount = 1, FixedRowCount = 2 }

        [SerializeField]
        protected Corner m_StartCorner = Corner.UpperLeft;
        public Corner startCorner { get { return m_StartCorner; } set { SetProperty(ref m_StartCorner, value); } }

        [SerializeField]
        protected Axis m_StartAxis = Axis.Horizontal;
        public Axis startAxis { get { return m_StartAxis; } set { SetProperty(ref m_StartAxis, value); } }

        [SerializeField]
        protected Vector2 m_CellSize = new Vector2(100, 100);
        public Vector2 cellSize { get { return m_CellSize; } set { SetProperty(ref m_CellSize, value); } }

        [SerializeField]
        protected Vector2 m_Spacing = Vector2.zero;
        public Vector2 spacing { get { return m_Spacing; } set { SetProperty(ref m_Spacing, value); } }

        [SerializeField]
        protected Constraint m_Constraint = Constraint.Flexible;
        public Constraint constraint { get { return m_Constraint; } set { SetProperty(ref m_Constraint, value); } }

        [SerializeField]
        protected int m_ConstraintCount = 2;
        public int constraintCount { get { return m_ConstraintCount; } set { SetProperty(ref m_ConstraintCount, Mathf.Max(1, value)); } }

        protected AutoExpandGridLayoutGroup()
        { }

        #if UNITY_EDITOR
        protected override void OnValidate()
        {
            base.OnValidate();
            constraintCount = constraintCount;
        }
        #endif

        protected override void OnRectTransformDimensionsChange(){
            base.OnRectTransformDimensionsChange ();
            float meSize = getPieceSquareCalculated (rectTransform.rect.size.y, rectTransform.rect.size.x, rectChildren.Count);
            m_CellSize = new Vector2 (meSize,meSize);
        }
        protected virtual void OnTransformChildrenChanged(){
            base.OnTransformChildrenChanged();
            float meSize = getPieceSquareCalculated (rectTransform.rect.size.y, rectTransform.rect.size.x, rectChildren.Count);
            m_CellSize = new Vector2 (meSize,meSize);
        }
        public override void CalculateLayoutInputHorizontal()
        {
            base.CalculateLayoutInputHorizontal();

            int minColumns = 0;
            int preferredColumns = 0;
            if (m_Constraint == Constraint.FixedColumnCount)
            {
                minColumns = preferredColumns = m_ConstraintCount;
            }
            else if (m_Constraint == Constraint.FixedRowCount)
            {
                minColumns = preferredColumns = Mathf.CeilToInt(rectChildren.Count / (float)m_ConstraintCount - 0.001f);
            }
            else
            {
                minColumns = 1;
                preferredColumns = Mathf.CeilToInt(Mathf.Sqrt(rectChildren.Count));
            }

            SetLayoutInputForAxis(
                padding.horizontal + (cellSize.x + spacing.x) * minColumns - spacing.x,
                padding.horizontal + (cellSize.x + spacing.x) * preferredColumns - spacing.x,
                -1, 0);
        }

        public override void CalculateLayoutInputVertical()
        {
            int minRows = 0;
            if (m_Constraint == Constraint.FixedColumnCount)
            {
                minRows = Mathf.CeilToInt(rectChildren.Count / (float)m_ConstraintCount - 0.001f);
            }
            else if (m_Constraint == Constraint.FixedRowCount)
            {
                minRows = m_ConstraintCount;
            }
            else
            {
                float width = rectTransform.rect.size.x;
                int cellCountX = Mathf.Max(1, Mathf.FloorToInt((width - padding.horizontal + spacing.x + 0.001f) / (cellSize.x + spacing.x)));
                minRows = Mathf.CeilToInt(rectChildren.Count / (float)cellCountX);
            }

            float minSpace = padding.vertical + (cellSize.y + spacing.y) * minRows - spacing.y;
            SetLayoutInputForAxis(minSpace, minSpace, -1, 1);
        }

        public override void SetLayoutHorizontal()
        {
            SetCellsAlongAxis(0);
        }

        public override void SetLayoutVertical()
        {
            SetCellsAlongAxis(1);
        }

        private void SetCellsAlongAxis(int axis)
        {
            // Normally a Layout Controller should only set horizontal values when invoked for the horizontal axis
            // and only vertical values when invoked for the vertical axis.
            // However, in this case we set both the horizontal and vertical position when invoked for the vertical axis.
            // Since we only set the horizontal position and not the size, it shouldn't affect children's layout,
            // and thus shouldn't break the rule that all horizontal layout must be calculated before all vertical layout.

            if (axis == 0)
            {
                // Only set the sizes when invoked for horizontal axis, not the positions.
                for (int i = 0; i < rectChildren.Count; i++)
                {
                    RectTransform rect = rectChildren[i];

                    m_Tracker.Add(this, rect,
                        DrivenTransformProperties.Anchors |
                        DrivenTransformProperties.AnchoredPosition |
                        DrivenTransformProperties.SizeDelta);

                    rect.anchorMin = Vector2.up;
                    rect.anchorMax = Vector2.up;
                    rect.sizeDelta = cellSize;
                }
                return;
            }

            float width = rectTransform.rect.size.x;
            float height = rectTransform.rect.size.y;

            int cellCountX = 1;
            int cellCountY = 1;
            if (m_Constraint == Constraint.FixedColumnCount)
            {
                cellCountX = m_ConstraintCount;
                cellCountY = Mathf.CeilToInt(rectChildren.Count / (float)cellCountX - 0.001f);
            }
            else if (m_Constraint == Constraint.FixedRowCount)
            {
                cellCountY = m_ConstraintCount;
                cellCountX = Mathf.CeilToInt(rectChildren.Count / (float)cellCountY - 0.001f);
            }
            else
            {
                if (cellSize.x + spacing.x <= 0)
                    cellCountX = int.MaxValue;
                else
                    cellCountX = Mathf.Max(1, Mathf.FloorToInt((width - padding.horizontal + spacing.x + 0.001f) / (cellSize.x + spacing.x)));

                if (cellSize.y + spacing.y <= 0)
                    cellCountY = int.MaxValue;
                else
                    cellCountY = Mathf.Max(1, Mathf.FloorToInt((height - padding.vertical + spacing.y + 0.001f) / (cellSize.y + spacing.y)));
            }

            int cornerX = (int)startCorner % 2;
            int cornerY = (int)startCorner / 2;

            int cellsPerMainAxis, actualCellCountX, actualCellCountY;
            if (startAxis == Axis.Horizontal)
            {
                cellsPerMainAxis = cellCountX;
                actualCellCountX = Mathf.Clamp(cellCountX, 1, rectChildren.Count);
                actualCellCountY = Mathf.Clamp(cellCountY, 1, Mathf.CeilToInt(rectChildren.Count / (float)cellsPerMainAxis));
            }
            else
            {
                cellsPerMainAxis = cellCountY;
                actualCellCountY = Mathf.Clamp(cellCountY, 1, rectChildren.Count);
                actualCellCountX = Mathf.Clamp(cellCountX, 1, Mathf.CeilToInt(rectChildren.Count / (float)cellsPerMainAxis));
            }

            Vector2 requiredSpace = new Vector2(
                actualCellCountX * cellSize.x + (actualCellCountX - 1) * spacing.x,
                actualCellCountY * cellSize.y + (actualCellCountY - 1) * spacing.y
            );
            Vector2 startOffset = new Vector2(
                GetStartOffset(0, requiredSpace.x),
                GetStartOffset(1, requiredSpace.y)
            );

            for (int i = 0; i < rectChildren.Count; i++)
            {
                int positionX;
                int positionY;
                if (startAxis == Axis.Horizontal)
                {
                    positionX = i % cellsPerMainAxis;
                    positionY = i / cellsPerMainAxis;
                }
                else
                {
                    positionX = i / cellsPerMainAxis;
                    positionY = i % cellsPerMainAxis;
                }

                if (cornerX == 1)
                    positionX = actualCellCountX - 1 - positionX;
                if (cornerY == 1)
                    positionY = actualCellCountY - 1 - positionY;

                float realsize = ((width - (spacing[0] * (actualCellCountX - 1))) / actualCellCountX);
                SetChildAlongAxis(rectChildren[i], 0, startOffset.x + (realsize + spacing[0]) * positionX, realsize);
                SetChildAlongAxis(rectChildren[i], 1, startOffset.y + (cellSize[1] + spacing[1]) * positionY, cellSize[1]);
            }
        }
        public static float getPieceSquareCalculated(float height, float width, int numberOfPieces)
        {
            float px = Mathf.Ceil(Mathf.Sqrt(numberOfPieces * width / height)) +1;
            px = px == 0 ? 1 : px;
            float sx, sy;
            if (Mathf.Floor(px * height / width) * px < numberOfPieces)
                sx = height / Mathf.Ceil(px * height / width);
            else
                sx = width / px;
            float py = Mathf.Ceil(Mathf.Sqrt(numberOfPieces * height / width))+1;
            py = py == 0 ? 1 : py;
            if (Mathf.Floor(py * width / height) * py < numberOfPieces)
                sy = width / Mathf.Ceil(width * py / height);
            else
                sy = height / py;
            return Mathf.Max(sx, sy);
        }
    }
}