On Tue, Aug 30, 2011 at 3:56 PM, Charles Pritchard <[email protected]> wrote: > On Aug 30, 2011, at 3:26 PM, "Tab Atkins Jr." <[email protected]> wrote: >> On Tue, Aug 30, 2011 at 3:19 PM, Charles Pritchard <[email protected]> wrote: >>> >>> I'd like to see a new property added to the TextMetrics object from Canvas >>> 2d. >>> >>> var t = ctx.measureText('text span'); >>> t == { width: int, baseline: int }; >>> >>> The baseline corresponds to the vertical offset of the anchor point. >>> A tiny number. It's not the same as height, but it has a similar use. >>> >>> It allows allows the author to manage style markers on spans of text >>> presenting different baselines. >>> >>> The following textBaseline image can not be generated in canvas: >>> https://developer.mozilla.org/en/drawing_text_using_a_canvas >>> http://www.whatwg.org/specs/web-apps/current-work/images/baselines.png >>> >>> It can, but we have to do css hacks/edge detection, as measureText is >>> insufficient. >>> By exposing the baseline offset in the TextMetrics method, we would be able >>> to generate >>> the lines in that image, and appropriately position the text captions. >>> >>> It seems appropriate that the illustration for textBaseline be something >>> that can be easily generated from within canvas. The same standard is held >>> for SVG documentation. >> >> Agreed, though there are multiple baselines that could be requested. >> The diagram you link to points out three of them. The alphabetic >> baseline is what you want most of the time, but all of them can be >> useful depending on the type of text you're formatting. > > The author would have to set ctx.textBaseline, and re-run TextMetrics for > each baseline they are incorporating. > > The enumeration of supported baselines is already in the canvas spec.
Okay, that's reasonable. ~TJ
