Target: Android >= 1.6 on a pure Canvas.
Suppose I want to write a function that will draw a (width, height) large red rectangle and then draw a black Hello World text inside. I want the text to be visually in the center of the rectangle. So let's try:
void drawHelloRectangle(Canvas c, int topLeftX, int topLeftY, int width, int height) { Paint mPaint = new Paint(); // height of 'Hello World'; height*0.7 looks good int fontHeight = (int)(height*0.7); mPaint.setColor(COLOR_RED); mPaint.setStyle(Style.FILL); c.drawRect( topLeftX, topLeftY, topLeftX+width, topLeftY+height, mPaint); mPaint.setTextSize(fontHeight); mPaint.setColor(COLOR_BLACK); mPaint.setTextAlign(Align.CENTER); c.drawText( "Hello World", topLeftX+width/2, ????, mPaint); }
Now I don't know what to put in drawText's argument marked by ????
, i.e. I don't know how to vertically align the text.
Something like
???? = topLeftY + height/2 + fontHeight/2 - fontHeight/8;
appears to work more or less ok, but there must be a better way.
To center both vertically and horizontally, use padding and text-align: center : I am vertically and horizontally centered.
Use the line-height Property to Align Text Vertically in CSS If we have single-line text, we can use the line-height property to align the text vertically within a div . The line-height CSS property sets the height of a line box. It is used to set the distance between lines of text.
cx
and cy
:private final Rect textBounds = new Rect(); //don't new this up in a draw method public void drawTextCentred(Canvas canvas, Paint paint, String text, float cx, float cy){ paint.getTextBounds(text, 0, text.length(), textBounds); canvas.drawText(text, cx - textBounds.exactCenterX(), cy - textBounds.exactCenterY(), paint); }
height()/2f
work the same?exactCentre()
= (top + bottom) / 2f
.
height()/2f
= (bottom - top) / 2f
These would only yield the same result when top
is 0
. This may be the case for some fonts at all sizes, or other fonts at some sizes, but not for all fonts at all sizes.
textY = topLeftY + height/2 - (mPaint.descent() + mPaint.ascent()) / 2
The distance from "baseline" to "center" should be -(mPaint.descent() + mPaint.ascent()) / 2
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