Font size problem about libjass HOT 3 CLOSED

1fcb8d6

In short, libjass creates <div>M</div>, then approximates its font size and measures the div's total height.

The code has moved since then and is currently at

// fontSizeElement is the <div>. lineHeight is the "font size" specified in the ASS script. actualFontSize is the CSS font size that needs to be calculated.
fontSizeElement.style.fontFamily = fontFamily;
fontSizeElement.style.fontSize = lineHeight + "px";
actualFontSize = lineHeight * lineHeight / fontSizeElement.offsetHeight;

from libjass.

Thanks a lot!

from libjass.

Note that this is only an approximation. I used to have a loop that tried to iteratively refine the answer (each iteration used the actualFontSize computed from the previous iteration until the lineHeight and fontSizeElement.offsetHeight were very close to each other), but I took it out because a) it's a blocking operation that stalls the browser in a loop, and b) the result from just one iteration is fairly accurate already.

The accuracy suffers for very large font sizes, since the equation basically assumes that the ratio of font size to line height is the same for two different font sizes. This is less true for large font sizes so it might be prudent to have more than one iteration for those.

from libjass.