Shrink效果

开发过程中很多地方会用到文字自动缩放的功能，有些是设计如此，有些是防止策划文字配置超出预定的个数。其实都是一种情况，要在显示区域固定的情况下，显示出所有文字，当显示不全的时候就要缩小字号。
　　UGUI的Text提供了Best Fit选项支持自动缩放，开启后Text会自动在[Min Size, Max Size]区间中选择“合适”的字号进行渲染。本来挺好的一个功能，却被做成了奇葩（越发怀念NGUI了）。
　　在实际使用的时候，基本Best Fit只取到了Min或Max两个值。因为当一行放不下所有文字的时候，UGUI就会缩小字号。最终的结果就是，要么是一行的Max大字，要么是多行的Min小字，中间的过度几乎看不到。
　　在这方面NGUI UILabel的ShrinkContent做的就比较好，整个显示区域无法容纳全部内容的时候，才会缩小字号。本文的解决方案也是借鉴NGUI来的：

public class ShrinkText : Text
{
    /// <summary>
    /// 当前可见的文字行数
    /// </summary>
    public int VisibleLines { get; private set; }

    private void _UseFitSettings()
    {
        TextGenerationSettings settings = GetGenerationSettings(rectTransform.rect.size);
        settings.resizeTextForBestFit = false;

        if (!resizeTextForBestFit)
        {
            cachedTextGenerator.Populate(text, settings);
            return;
        }

        int minSize = resizeTextMinSize;
        int txtLen = text.Length;
        for (int i = resizeTextMaxSize; i >= minSize; --i)
        {
            settings.fontSize = i;
            cachedTextGenerator.Populate(text, settings);
            if (cachedTextGenerator.characterCountVisible == txtLen) break;
        }
    }

    private readonly UIVertex[] _tmpVerts = new UIVertex[4];
    protected override void OnPopulateMesh(VertexHelper toFill)
    {
        if (null == font) return;

        m_DisableFontTextureRebuiltCallback = true;
        _UseFitSettings();
        Rect rect = rectTransform.rect;
        
        Vector2 textAnchorPivot = GetTextAnchorPivot(alignment);
        Vector2 zero = Vector2.zero;
        zero.x = Mathf.Lerp(rect.xMin, rect.xMax, textAnchorPivot.x);
        zero.y = Mathf.Lerp(rect.yMin, rect.yMax, textAnchorPivot.y);
        Vector2 vector2 = PixelAdjustPoint(zero) - zero;
        IList<UIVertex> verts = cachedTextGenerator.verts;
        float num1 = 1f / pixelsPerUnit;
        int num2 = verts.Count - 4;
        toFill.Clear();
        if (vector2 != Vector2.zero)
        {
            for (int index1 = 0; index1 < num2; ++index1)
            {
                int index2 = index1 & 3;
                _tmpVerts[index2] = verts[index1];
                _tmpVerts[index2].position *= num1;
                _tmpVerts[index2].position.x += vector2.x;
                _tmpVerts[index2].position.y += vector2.y;
                if (index2 == 3)
                    toFill.AddUIVertexQuad(this._tmpVerts);
            }
        }
        else
        {
            for (int index1 = 0; index1 < num2; ++index1)
            {
                int index2 = index1 & 3;
                _tmpVerts[index2] = verts[index1];
                _tmpVerts[index2].position *= num1;
                if (index2 == 3)
                    toFill.AddUIVertexQuad(_tmpVerts);
            }
        }
        m_DisableFontTextureRebuiltCallback = false;
        VisibleLines = cachedTextGenerator.lineCount;
    }
}

[2021-03-30 更新]

新项目使用Unity2020.3.1f1，发现这个脚本会少一个字符，大概看了下Text源码改了，把内容相应复制一下即可解决。变化的内容暂不深究了，没啥时间。

private void _UseFitSettings()
{
    TextGenerationSettings settings = GetGenerationSettings(rectTransform.rect.size);
    settings.resizeTextForBestFit = false;

    if (!resizeTextForBestFit)
    {
        cachedTextGenerator.PopulateWithErrors(text, settings, gameObject);
        return;
    }

    int minSize = resizeTextMinSize;
    int txtLen = text.Length;
    for (int i = resizeTextMaxSize; i >= minSize; --i)
    {
        settings.fontSize = i;
        cachedTextGenerator.PopulateWithErrors(text, settings, gameObject);
        if (cachedTextGenerator.characterCountVisible == txtLen) break;
    }
}

protected override void OnPopulateMesh(VertexHelper toFill)
{
    if (null == font) return;

    m_DisableFontTextureRebuiltCallback = true;
    _UseFitSettings();

    // Apply the offset to the vertices
    IList<UIVertex> verts = cachedTextGenerator.verts;
    float unitsPerPixel = 1 / pixelsPerUnit;
    int vertCount = verts.Count;

    // We have no verts to process just return (case 1037923)
    if (vertCount <= 0)
    {
        toFill.Clear();
        return;
    }

    Vector2 roundingOffset = new Vector2(verts[0].position.x, verts[0].position.y) * unitsPerPixel;
    roundingOffset = PixelAdjustPoint(roundingOffset) - roundingOffset;
    toFill.Clear();
    if (roundingOffset != Vector2.zero)
    {
        for (int i = 0; i < vertCount; ++i)
        {
            int tempVertsIndex = i & 3;
            _tmpVerts[tempVertsIndex] = verts[i];
            _tmpVerts[tempVertsIndex].position *= unitsPerPixel;
            _tmpVerts[tempVertsIndex].position.x += roundingOffset.x;
            _tmpVerts[tempVertsIndex].position.y += roundingOffset.y;
            if (tempVertsIndex == 3)
                toFill.AddUIVertexQuad(_tmpVerts);
        }
    }
    else
    {
        for (int i = 0; i < vertCount; ++i)
        {
            int tempVertsIndex = i & 3;
            _tmpVerts[tempVertsIndex] = verts[i];
            _tmpVerts[tempVertsIndex].position *= unitsPerPixel;
            if (tempVertsIndex == 3)
                toFill.AddUIVertexQuad(_tmpVerts);
        }
    }

    m_DisableFontTextureRebuiltCallback = false;
    VisibleLines = cachedTextGenerator.lineCount;
}