Canvas 作爲繪製文本時,是以基線爲基準繪製的,不是左上角
FontMetrics對象
它以四個基本座標爲基準,分別爲:
・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對象
FontMetrics fontMetrics = textPaint.getFontMetrics();
String text = "abcdefghijklmnopqrstu";
// 計算每一個座標
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;
// 繪製文本
canvas.drawText( text, baseX, baseY, textPaint);
// BaseLine描畫
Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);>
baseLinePaint.setColor( Color.RED);
canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint);
// Base描畫
canvas.drawCircle( baseX, baseY, 5, baseLinePaint);
// TopLine描畫
Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
topLinePaint.setColor( Color.LTGRAY);
canvas.drawLine(0, topY, getWidth(), topY, topLinePaint);
// AscentLine描畫
Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
ascentLinePaint.setColor( Color.GREEN);
canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint);
// DescentLine描畫
Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
descentLinePaint.setColor( Color.YELLOW);
canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint);
// ButtomLine描畫
Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
bottomLinePaint.setColor( Color.MAGENTA);
canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);