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SkiaTextLayout.cs
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SkiaTextLayout.cs
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using System;
using System.Collections.Generic;
using SkiaSharp;
namespace Microsoft.Maui.Graphics.Skia
{
public class SkiaTextLayout : IDisposable
{
private readonly LayoutLine _callback;
private readonly RectF _rect;
private readonly ITextAttributes _textAttributes;
private readonly string _value;
private readonly TextFlow _textFlow;
private readonly SKPaint _paint;
private readonly bool _disposePaint;
private readonly float _lineHeight;
private readonly float _descent;
public bool WordWrap { get; set; } = true;
public SkiaTextLayout(
string value,
RectF rect,
ITextAttributes textAttributes,
LayoutLine callback,
TextFlow textFlow = TextFlow.ClipBounds,
SKPaint paint = null)
{
_value = value;
_textAttributes = textAttributes;
_rect = rect;
_callback = callback;
_textFlow = textFlow;
_paint = paint;
if (paint == null)
{
_paint = new SKPaint()
{
Typeface = _textAttributes?.Font?.ToSKTypeface() ?? SKTypeface.Default,
TextSize = _textAttributes.FontSize
};
_disposePaint = true;
}
var metrics = _paint.FontMetrics;
_descent = metrics.Descent;
_lineHeight = _paint.FontSpacing;
}
public void LayoutText()
{
if (string.IsNullOrEmpty(_value))
return;
var x = _rect.X;
var y = _rect.Y;
var width = _rect.Width;
var height = _rect.Height;
x += _textAttributes.Margin;
y += _textAttributes.Margin;
width -= (_textAttributes.Margin * 2);
height -= (_textAttributes.Margin * 2);
var top = y;
var bottom = y + height;
if (_textAttributes.HorizontalAlignment == HorizontalAlignment.Right)
_paint.TextAlign = SKTextAlign.Right;
else if (_textAttributes.HorizontalAlignment == HorizontalAlignment.Center)
_paint.TextAlign = SKTextAlign.Center;
var lines = CreateLines(y, bottom, width);
switch (_textAttributes.VerticalAlignment)
{
case VerticalAlignment.Center:
LayoutCenterAligned(lines, x, width, top, height);
break;
case VerticalAlignment.Bottom:
LayoutBottomAligned(lines, x, width, bottom, top);
break;
default:
LayoutTopAligned(lines, x, y, width);
break;
}
_paint.TextAlign = SKTextAlign.Left;
}
private void LayoutCenterAligned(
List<TextLine> lines,
float x,
float width,
float top,
float height)
{
var linesToDraw = lines.Count;
if (_textFlow == TextFlow.ClipBounds)
{
var maxLines = Math.Floor(height / _lineHeight);
linesToDraw = (int)Math.Min(maxLines, lines.Count);
}
// Figure out the vertical center of the rect
var y = top + height / 2;
// Figure out the center index of the list, and the center point to start drawing from.
var startIndex = (lines.Count / 2);
if (linesToDraw % 2 != 0)
y -= _lineHeight / 2;
// Figure out which index to draw first (of the range) and the point of the first line.
for (var i = 0; i < linesToDraw / 2; i++)
{
y -= _lineHeight;
startIndex--;
}
y -= _descent;
// Draw each line.
for (var i = 0; i < linesToDraw; i++)
{
y += _lineHeight;
var line = lines[i + startIndex];
var point = new PointF(x, y);
switch (_textAttributes.HorizontalAlignment)
{
case HorizontalAlignment.Center:
point.X = x + width / 2;
break;
case HorizontalAlignment.Right:
point.X = x + width;
break;
}
_callback(point, _textAttributes, line.Value, 0, 0, 0);
}
}
private void LayoutBottomAligned(
List<TextLine> lines,
float x,
float width,
float bottom,
float top)
{
var y = bottom - _descent;
for (int i = lines.Count - 1; i >= 0; i--)
{
var line = lines[i];
if (_textFlow == TextFlow.ClipBounds && y - _lineHeight < top)
return;
var point = new PointF(x, y);
switch (_textAttributes.HorizontalAlignment)
{
case HorizontalAlignment.Center:
point.X = x + width / 2;
break;
case HorizontalAlignment.Right:
point.X = x + width;
break;
}
_callback(point, _textAttributes, line.Value, 0, 0, 0);
y -= _lineHeight;
}
}
private void LayoutTopAligned(
List<TextLine> lines,
float x,
float y,
float width)
{
y -= _descent;
foreach (var line in lines)
{
y += _lineHeight;
var point = new PointF(x, y);
switch (_textAttributes.HorizontalAlignment)
{
case HorizontalAlignment.Center:
point.X = x + width / 2;
break;
case HorizontalAlignment.Right:
point.X = x + width;
break;
}
_callback(point, _textAttributes, line.Value, 0, 0, 0);
}
}
private List<TextLine> CreateLines(float y, float bottom, float width)
{
var lines = new List<TextLine>();
var index = 0;
var length = _value.Length;
while (index < length)
{
y += _lineHeight;
if (_textFlow == TextFlow.ClipBounds && _textAttributes.VerticalAlignment == VerticalAlignment.Top && y > bottom)
return lines;
var count = (int)_paint.BreakText(_value.Substring(index), width, out var textWidth);
var found = false;
if (WordWrap && index + count < length)
{
for (var i = index + count - 1; i >= index && !found; i--)
{
if (char.IsWhiteSpace(_value[i]))
{
count = i - index + 1;
found = true;
}
}
}
var line = _value.Substring(index, count);
if (found)
textWidth = _paint.MeasureText(line);
lines.Add(new TextLine(line, textWidth));
index += count;
}
return lines;
}
public void Dispose()
{
if (_disposePaint)
_paint?.Dispose();
}
}
public class TextLine
{
public string Value { get; }
public float Width { get; }
public TextLine(
string value,
float width)
{
Value = value;
Width = width;
}
}
}