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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.

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  • 21
    Every time you put Android in the question title a kitten will die so please stop doing that. Thanks. Commented Feb 5, 2011 at 20:20
  • 1
    9 years later, this question and the accepted answer are still relevant Commented Jul 31, 2020 at 1:38

9 Answers 9

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Example to centre on 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); }

Why doesn't 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.

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15 Comments

This should be the accepted answer. Not only it's the simplest one of them all, it's the only one that really, optically centers the text vertically, properly taking ascents and descents into account (not generally but the actual ones present in the actual text to be displayed).
Been through a lot of hoops and loops to crack this - and then its as simple as this. This is the answer you are looking for!
Can someone tell me why textBounds.height() / 2 doesn't work as expected? (At least not for me.) I found this answer and replaced height() with centerY() and now it works...
1. First the code does not take into account the alignment of the text (for example it will not work if align is CENTER) 2. As this method simply translate the center of the text's bounds when we actually paint the text it will not fit the bounds (not considering ascent and descent of the text)
@Alex it does what it does, I'm sorry if it doesn't fit your requirements. "when we actually paint the text it will not fit the bounds" it fits the bounds, we just moved the centre.
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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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2 Comments

This didn't work for me but the accepted answer worked perfectly. Maybe the result this approach looks better if the font is smaller.
I tried a few techniques in this question and found yours is the best overall. Unlike the accepted answer, this one provides consistent results regardless of what your text is. And also unlike the accepted answer, yours centres relative to a capital letter's mid-point, which I think is what most people would expect.
23

Based on steelbytes' response, the updated code would look something like:

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); String textToDraw = new String("Hello World"); Rect bounds = new Rect(); mPaint.getTextBounds(textToDraw, 0, textToDraw.length(), bounds); c.drawText(textToDraw, topLeftX+width/2, topLeftY+height/2+(bounds.bottom-bounds.top)/2, mPaint); }
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17

Since drawing text at Y means that the baseline of the text will end up Y pixels down from the origin, what you need to do when you want to center text within a rectangle of (width, height) dimensions is:

paint.setTextAlign(Paint.Align.CENTER); // centers horizontally canvas.drawText(text, width / 2, (height - paint.ascent()) / 2, paint);

Keep in mind that the ascent is negative (which explains the minus sign).

This does not take the descent into account, which is usually what you want (the ascent is generally the height of caps above the baseline).

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1 Comment

I just tried this answer but found that the text wasn't centred relative to capital letters like you suggested. Instead, I had to also use descent() to get this behaviour.
9

using mPaint.getTextBounds() you can ask how big the text will be when drawn, then using that info you can calc where you want to draw it.

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4 Comments

getTextBounds() belongs to Paint, not Canvas
Remember that when you say vertically centered text you probably mean around the ascending portion of the character, not the baseline. When you draw using Align.CENTER the Y-coordinate will center on the character baseline.
@CameronLowellPalmer Could you elaborate a bit more on that?
@Peterdk I recommend you try this for yourself, but what you are measuring is the bounds of drawn text. That means if the text descends below the baseline and you are lining up several, separately drawn words, you are going to have text that doesn't line up the way you expect.The word 'grow' descends below the baseline, the word 'hi' does not. So if you find the center of the TextBounds of those two words and then divide by 2 to find the height you will get an undesirable result.
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public static PointF getTextCenterToDraw(String text, RectF region, Paint paint) { Rect textBounds = new Rect(); paint.getTextBounds(text, 0, text.length(), textBounds); float x = region.centerX() - textBounds.width() * 0.4f; float y = region.centerY() + textBounds.height() * 0.4f; return new PointF(x, y); }

Usage:

PointF p = getTextCenterToDraw(text, rect, paint); canvas.drawText(text, p.x, p.y, paint);
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1

I stumbled on this question when trying to solve my issue, and @Weston's answer works fine with me.

In case of Kotlin: 

private fun drawText(canvas: Canvas) { paint.textSize = 80f val text = "Hello!" val textBounds = Rect() paint.getTextBounds(text, 0, text.length, textBounds); canvas.drawText(text, cx- textBounds.exactCenterX(), cy - textBounds.exactCenterY(), paint); //in case of another Rect as a container: //canvas.drawText(text, containerRect.exactCenterX()- textBounds.exactCenterX(), containerRect.exactCenterY() - textBounds.exactCenterY(), paint); }
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1

Here is a SkiaSharp C# extension method for anyone looking for it 

public static void DrawTextCenteredVertically(this SKCanvas canvas, string text, SKPaint paint, SKPoint point) { var textY = point.Y + (((-paint.FontMetrics.Ascent + paint.FontMetrics.Descent) / 2) - paint.FontMetrics.Descent); canvas.DrawText(text, point.X, textY, paint); }
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0 
private final Rect textBounds = new Rect();//No need o create again public void drawTextCentred(Canvas canvas, Paint paint, String text, float cx, float cy, float desiredWidth) { final float testTextSize = 48f; paint.setTextSize(testTextSize); Rect bounds = new Rect(); paint.getTextBounds(text, 0, text.length(), bounds); float desiredTextSize = testTextSize * desiredWidth / bounds.width(); paint.setTextSize(desiredTextSize); paint.getTextBounds(text, 0, text.length(), textBounds); paint.setTextAlign(Paint.Align.CENTER); canvas.drawText(text, cx, cy - textBounds.exactCenterY(), paint); }
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1 Comment

Please don't post only code as answer, but also provide an explanation what your code does and how it solves the problem of the question. Answers with an explanation are usually more helpful and of better quality, and are more likely to attract upvotes.

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