How text works in canvas
Unfortunately no, you can’t produce text with background with the text methods – only fill or outline the text itself.
This is because the glyphs from the typeface (font) are converted to individual shapes or paths if you want, where the background of it would be the inner part of the glyph itself (the part you see when using fill). There is no layer for the black-box (the rectangle which the glyph fits within) the glyph is using besides from using its geometric position, so we need to provide a sort-of black-box and bearings ourselves.
On the old computer systems most fonts where binary font which where setting or clearing a pixels. Instead of just clearing the background one could opt to provide a background instead. This is not the case with vector based typefaces by default (a browser has direct access to the glyphs geometry and can therefor provide a background this way).
Creating custom background
In order to create a background you would need to draw it first using other means such as shapes or an image.
Examples:
ctx.fillRect(x, y, width, height);
or
ctx.drawImage(image, x, y [, width, height]);
then draw the text on top:
ctx.fillText('My text', x, y);
You can use measureText
to find out the width of the text (in the future also the height: ascend + descend) and use that as a basis:
var width = ctx.measureText('My text').width; /// width in pixels
You can wrap all this in a function. The function here is basic but you can expand it with color and background parameters as well as padding etc.
/// expand with color, background etc.
function drawTextBG(ctx, txt, font, x, y) {
/// lets save current state as we make a lot of changes
ctx.save();
/// set font
ctx.font = font;
/// draw text from top - makes life easier at the moment
ctx.textBaseline="top";
/// color for background
ctx.fillStyle="#f50";
/// get width of text
var width = ctx.measureText(txt).width;
/// draw background rect assuming height of font
ctx.fillRect(x, y, width, parseInt(font, 10));
/// text color
ctx.fillStyle="#000";
/// draw text on top
ctx.fillText(txt, x, y);
/// restore original state
ctx.restore();
}
ONLINE DEMO HERE
Just note that this way of “measuring” height is not accurate. You can measure height of a font by using a temporary div/span element and get the calculated style from that when font and text is set for it.