The TextMetrics
interface represents the dimensions of a piece of text in the canvas; a textMetrics()
instance can be retrieved using the CanvasRenderingContext2D.measureText()
method.
Properties
TextMetrics.width
Read only- Is a
double
giving the calculated width of a segment of inline text in CSS pixels. It takes into account the current font of the context. TextMetrics.actualBoundingBoxLeft
Read only- Is a
double
giving the distance from the alignment point given by theCanvasRenderingContext2D.textAlign
property to the left side of the bounding rectangle of the given text, in CSS pixels. The distance is measured parallel to the baseline. TextMetrics.actualBoundingBoxRight
Read only- Is a
double
giving the distance from the alignment point given by theCanvasRenderingContext2D.textAlign
property to the right side of the bounding rectangle of the given text, in CSS pixels. The distance is measured parallel to the baseline. TextMetrics.fontBoundingBoxAscent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
attribute to the top of the highest bounding rectangle of all the fonts used to render the text, in CSS pixels. TextMetrics.fontBoundingBoxDescent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
attribute to the bottom of the bounding rectangle of all the fonts used to render the text, in CSS pixels. TextMetrics.actualBoundingBoxAscent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
attribute to the top of the bounding rectangle used to render the text, in CSS pixels. TextMetrics.actualBoundingBoxDescent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
attribute to the bottom of the bounding rectangle used to render the text, in CSS pixels. TextMetrics.emHeightAscent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
property to the top of the em square in the line box, in CSS pixels. TextMetrics.emHeightDescent
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
property to the bottom of the em square in the line box, in CSS pixels. TextMetrics.hangingBaseline
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
property to the hanging baseline of the line box, in CSS pixels. TextMetrics.alphabeticBaseline
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
property to the alphabetic baseline of the line box, in CSS pixels. TextMetrics.ideographicBaseline
Read only- Is a
double
giving the distance from the horizontal line indicated by theCanvasRenderingContext2D.textBaseline
property to the ideographic baseline of the line box, in CSS pixels.
Examples
Baselines illustrated
This example demonstrates the baselines the TextMetrics
object holds. The default baseline is the alphabeticBaseline
. See also the CanvasRenderingContext2D.textBaseline
property.
HTML
<canvas id="canvas" width="550" height="500"></canvas>
JavaScript
const canvas = document.getElementById('canvas'); const ctx = canvas.getContext('2d'); const baselinesAboveAlphabetic = ['fontBoundingBoxAscent', 'actualBoundingBoxAscent', 'emHeightAscent', 'hangingBaseline']; const baselinesBelowAlphabetic = ['ideographicBaseline', 'emHeightDescent', 'actualBoundingBoxDescent', 'fontBoundingBoxDescent']; const baselines = [...baselinesAboveAlphabetic, ...baselinesBelowAlphabetic]; ctx.font = '25px serif'; ctx.strokeStyle = 'red'; baselines.forEach(function (baseline, index) { let text = 'Abcdefghijklmnop (' + baseline + ')'; let textMetrics = ctx.measureText(text); let y = 50 + index * 50; ctx.beginPath(); ctx.fillText(text, 0, y); let lineY = y - Math.abs(textMetrics[baseline]); if (baselinesBelowAlphabetic.includes(baseline)) { lineY = y + Math.abs(textMetrics[baseline]); } ctx.moveTo(0, lineY); ctx.lineTo(550, lineY); ctx.stroke(); });
Result
Measuring text width
When measuring the x-direction of a piece of text, the sum of actualBoundingBoxLeft
and actualBoundingBoxRight
can be wider than the width of the inline box (width
), due to slanted/italic fonts where characters overhang their advance width.
It can therefore be useful to use the sum of actualBoundingBoxLeft
and actualBoundingBoxRight
as a more accurate way to get the absolute text width:
const canvas = document.getElementById('canvas'); const ctx = canvas.getContext('2d'); const text = 'Abcdefghijklmnop'; ctx.font = 'italic 50px serif'; const textMetrics = ctx.measureText(text); console.log(textMetrics.width); // 459.8833312988281 console.log(Math.abs(textMetrics.actualBoundingBoxLeft) + Math.abs(textMetrics.actualBoundingBoxRight)); // 462.8833333333333
Specifications
Specification |
---|
HTML Living Standard The definition of 'TextMetrics' in that specification. |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
TextMetrics | Chrome Full support 4 | Edge Full support 12 | Firefox Full support 1.5 | IE Full support 9 | Opera Full support 9 | Safari Full support 3.1 | WebView Android Full support Yes | Chrome Android Full support Yes | Firefox Android Full support 31 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes |
actualBoundingBoxAscent | Chrome
Full support
77
| Edge Full support 79 | Firefox Full support 74 | IE No support No | Opera ? | Safari Full support Yes | WebView Android Full support 77 | Chrome Android
Full support
77
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android Full support 12.0 |
actualBoundingBoxDescent | Chrome
Full support
77
| Edge Full support 79 | Firefox Full support 74 | IE No support No | Opera ? | Safari Full support Yes | WebView Android Full support 77 | Chrome Android
Full support
77
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android Full support 12.0 |
actualBoundingBoxLeft | Chrome
Full support
77
| Edge Full support 79 | Firefox Full support 74 | IE No support No | Opera ? | Safari Full support Yes | WebView Android Full support 77 | Chrome Android
Full support
77
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android Full support 12.0 |
actualBoundingBoxRight | Chrome
Full support
77
| Edge Full support 79 | Firefox Full support 74 | IE No support No | Opera ? | Safari Full support Yes | WebView Android Full support 77 | Chrome Android
Full support
77
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android Full support 12.0 |
alphabeticBaseline | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
emHeightAscent | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
emHeightDescent | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
fontBoundingBoxAscent | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
fontBoundingBoxDescent | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS No support No | Samsung Internet Android No support No |
hangingBaseline | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
ideographicBaseline | Chrome
Full support
Yes
| Edge
Full support
79
| Firefox
Full support
74
| IE No support No | Opera ? | Safari Full support Yes | WebView Android No support No | Chrome Android
Full support
Yes
| Firefox Android No support No | Opera Android ? | Safari iOS Full support Yes | Samsung Internet Android No support No |
width | Chrome Full support 4 | Edge Full support 12 | Firefox Full support 1.5 | IE Full support 9 | Opera Full support 9 | Safari Full support 3.1 | WebView Android Full support Yes | Chrome Android Full support Yes | Firefox Android Full support 31 | Opera Android Full support Yes | Safari iOS Full support 3.2 | Samsung Internet Android Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.
- User must explicitly enable this feature.
- User must explicitly enable this feature.
See also
- Creator method in
CanvasRenderingContext2D
- The
<canvas>
element and its associated interface,HTMLCanvasElement