android drawText

Canvas 作为绘制文本时，是以基线为基准绘制的，不是左上角

FontMetrics对象

它以四个基本坐标为基准，分别为：

・FontMetrics.top

・FontMetrics.ascent

・FontMetrics.descent

・FontMetrics.bottom

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示例：

Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);

textPaint.setTextSize( 35);

textPaint.setColor( Color.WHITE);

// FontMetrics对象

FontMetrics fontMetrics = textPaint.getFontMetrics();

String text = "abcdefghijklmnopqrstu";

// 计算每一个坐标

float baseX = 0;

float baseY = 100;

float topY = baseY + fontMetrics.top;

float ascentY = baseY + fontMetrics.ascent;

float descentY = baseY + fontMetrics.descent;

float bottomY = baseY + fontMetrics.bottom;

// 绘制文本

canvas.drawText( text, baseX, baseY, textPaint);

// BaseLine描画

Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);>

baseLinePaint.setColor( Color.RED);

canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint);

// Base描画

canvas.drawCircle( baseX, baseY, 5, baseLinePaint);

// TopLine描画

Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);

topLinePaint.setColor( Color.LTGRAY);

canvas.drawLine(0, topY, getWidth(), topY, topLinePaint);

// AscentLine描画

Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);

ascentLinePaint.setColor( Color.GREEN);

canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint);

// DescentLine描画

Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);

descentLinePaint.setColor( Color.YELLOW);

canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint);

// ButtomLine描画

Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);

bottomLinePaint.setColor( Color.MAGENTA);

canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);