Re: fontSize and percentages

Almost.  See corrections/comments inline below.


On Tue, Aug 20, 2013 at 1:58 AM, De Muyter, Yves (Contractor) <
Yves.DeMuyter@eu.sony.com> wrote:

> I can make following conclusion:****
>
> ** **
>
> used tts:fontSize=”75%”****
>
> default tts:fontSize=”1c”****
>
> cellResolution=”16 32”
>

Keep in mind that the default cellResolution is "32 15", meaning 32 columns
and 15 rows. Columns is specified first, rows second. I will assume that in
this example you are specifying a non-default cell resolution and that you
reversed the values, i.e., you should have said "32 16" if you meant 32
columns and 16 rows.


> ****
>
> tt extend=”640px 480px”
>

I assume that here you mean tts:extent="640px 480px" on the root <tt/>
element.


> ****
>
> ** **
>
> scaleH = scaling factor to scale emH to 480/16 ( = 1c height )
>

It would be better to restate this as follows:

(1) tts:fontSize="75%" (on some content element E) is resolved to a
computed value of 22.5px as follows:

   - if the region R into which E is select in a synchronic intermediate
   document does not specify a font size, then the initial value of 1c applies
   to the region R, and, as a consequence, the computed value of fontSize on R
   is 30px (480px/16);
   - every other ancestor A of E up to (but not including) R, inherits this
   value of 30px to form the computed value of fontSIze for A (provided A does
   not specify a font size itself);
   - the value 75% on E is resolved according to its immediate ancestor A',
   to 30px * 75% = 22.5px;

(2) scaleH = scaling factor to scale emH to 22.5px;


> ****
>
> ** **
>
> font height:  (scaleH * emH) * 75%****
>
> font width: (*scaleH* * emW) * 75%
>

Given the above, best restate this as:

(1) computed font height of E: 22.5px
(2) computed font width of E: 22.5px
(3) scale font isomorphically so that EM square is 22.5px in height


> ****
>
> ** **
>
> where emH = em height and em W = em width, the constants from the font
> chosen.****
>
> ** **
>
> Is it so that if I would use tts:fontSize=”75% 75%”, it would
> mathematically mean it’s deducted from a default that is tts:fontSize=”1c
> 1c”  and hence have following formulas ?****
>
> ** **
>
> scaleW = scaling factor to scale emW to 640/32 ( = 1c width )****
>
> ** **
>
> font height:  (scaleH * emH) * 75%****
>
> font width: (scaleW * emW) * 75%
>

Using the above corrections, this would be best stated as:

(1) computed font height of E: 22.5px
(2) computed font width of E: 15px
(3) scale font anamorphically so that EM square is 22.5px in height and
15px in width


> Thanks****
>
> ** **
>
> Yves****
>
> ** **
>
> *From:* Glenn Adams [mailto:glenn@skynav.com]
> *Sent:* 19 August 2013 17:45
> *To:* Nigel Megitt
> *Cc:* De Muyter, Yves (Contractor); public-tt@w3.org
> *Subject:* Re: fontSize and percentages****
>
> ** **
>
> ** **
>
> On Mon, Aug 19, 2013 at 8:19 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
> wrote:****
>
> Yves' question has highlighted that there's ambiguity in the current spec.
> Before we raise this as an issue is there some wording I've missed that
> says that EM cell aspect ratio should be preserved when one length
> specification is provided?****
>
> ** **
>
> This is equivalent to saying "If a single <length><http://www.w3.org/TR/ttaf1-dfxp/#style-value-length> value
> is specified, then this length applies equally to horizontal and vertical
> scaling of a glyph's EM square".****
>
> ** **
>
>  ****
>
> My search yielded zero results.****
>
> ** **
>
> For reference, my understanding of the words as currently written in 8.2.9
> is as follows:****
>
>    - When length is specified in percentage, this is (as in the table in
>    8.2.9) "relative to parent element's font size, or if no parent element,
>    then relative to the *Computed Cell Size"*****
>    - In this example there's no parent element font size so it's relative
>    to the cell size, which is 20px (width) x 32 px (height).****
>
> When you say "it's relative", it refers only to the process of resolving
> percentage specifications. It does not imply that the EM cell is the same
> as the TTML cell size, and also doesn't imply anything about the aspect
> ratio of the EM cell.****
>
> ** **
>
> See the note in 6.2.1:****
>
> ** **
>
> "The use of a uniform grid is employed only for the purpose of measuring
> lengths and expressing coordinates. In particular, it is not assumed that
> the presentation of text or the alignment of individual glyph areas is
> coordinated with this grid. Such alignment is possible, but requires the
> use of a monospaced font and a font size whose EM square exactly matches
> the cell size."****
>
>
>    - This sets the 100% size of the glyph's EM square, which in this case
>    is not square but rectangular. [I suspect this is the point of divergence
>    in the interpretation]****
>
> I'm not exactly sure what you mean by "this" in "This sets ...".****
>
> ** **
>
> In the case of outline fonts, the EM square is always square. In font
> files, e.g., OpenType, the EM square is associated with a coordinates space
> by specifying a resolution on this square, for OTF, this is unitsPerEm,
> defined in the 'head' table [1].****
>
> ** **
>
> This resolution is always uniform in both dimensions. In many Postscript
> based fonts, this is specified as 1000. In many OpenType and TrueType
> fonts, this is specified as 2048; however, the number can vary from 16 to
> 16384, as determined by font designer. Each glyph's outline is specified in
> coordinates within this coordinate space (but notes that outline points are
> not constrained to be interior to the EM square).****
>
> ** **
>
> [1] http://www.microsoft.com/typography/otspec/head.htm****
>
> ** **
>
> In the case of bitmap fonts, one may have a non-square "EM square", though
> here, the EM square is generally associated with a font bounding box, whose
> width and height can be construed as the EM square. For example, one might
> have for a BDF font [2] the following:****
>
> ** **
>
> FONTBOUNDINGBOX 16 16 0 -2****
>
> ** **
>
> [2] http://en.wikipedia.org/wiki/Glyph_Bitmap_Distribution_Format****
>
> ** **
>
> Here, one could create a double height font using a bounding box of, say:*
> ***
>
> ** **
>
> FONTBOUNDINGBOX 16 32 0 0****
>
> ** **
>
> or one that corresponds to the example "cell size" in this thread:****
>
> ** **
>
> FONTBOUNDINGBOX 15 24 0 0****
>
> ** **
>
> So, let's say we are using a bitmap font whose bounding box is 16px by
> 16px (square) with this example file whose cell size is 15px by 32px
> (non-square). Then a fontSize="75%" is the same as specifying font size of
> (32px * 75%) 24px. So, we need to scale this font by (24/16) 150% in both
> width and height.****
>
> ** **
>
> Let's say that instead we had specified fontSize="75% 75%", then this is
> the same as specifying of (15px * 75%) 11px (rounding to nearest integer)
> width and (32px * 75%) 24px height, i.e., the same as fontSize="11px 24px".
> So, we need to scale this font by (11/16) 68.75% in width and (24/16) 150%
> in height.****
>
> ** **
>
> So, we have:****
>
> ** **
>
> fontSize="75%"     : scale(24/16,24/16) : scale(150%,150%)****
>
> fontSize="75% 75%" : scale(11/16,24/16) : scale(69%,150%)****
>
> ** **
>
> If instead, we used a bitmap font whose bounding box is 7px by 16px
> (non-square), then we would arrive at:****
>
> ** **
>
> fontSize="75%"     : scale(24/16,24/16) : scale(150%,150%)****
>
> fontSize="75% 75%" : scale(11/7,24/16)  : scale(157%,150%)****
>
> ** **
>
>
>    - The wording "If a single <length><http://www.w3.org/TR/ttaf1-dfxp/#style-value-length>value is specified, then this length applies equally to horizontal and
>    vertical scaling of a glyph's EM square" for a percentage means that the
>    same percentage scaling is applied to both dimensions.****
>    - The note "The expression 1c means one cell, where 'c' expresses the *
>    cell* length unit as defined by *8.3.9 <length>*<http://www.w3.org/TR/ttaf1-dfxp/#style-value-length>.
>    When a single <length> is expressed using cell units, then it refers to the
>    height of the *Computed Cell Size*." does *not* apply because the
>    length is expressed in percentages not cell units.****
>    - Therefore the width is 640/32 * 75%.****
>
> I'd also note that I agree that the desired behaviour should primarily be
> to select a font with the required height (or as close to it as possible)
> and if any scaling is to be applied, do so equally in both dimensions if
> the scaling factor is the same in both dimensions, regardless of whether
> one or two values are provided. ****
>
> ** **
>
> No. If two values are specified, then scaling is independent in width and
> height.****
>
>  ****
>
> ** **
>
> The wording in 8.3.9 is perhaps a model for this: "When specified relative
> to a font whose size is expressed as a single length measure or as two
> length measures of equal length, the unit of measure em is considered to
> be identical to that defined by [XSL 1.1]<http://www.w3.org/TR/ttaf1-dfxp/#xsl11>,
> § 5.9.13; however, when specified relative to a font whose size is
> expressed as two length measures of non-equal lengths, then one em is
> equal to the inline progression dimension of the anamorphically scaled font
> when used to specify lengths in the inline progression direction and equal
> to the block progression dimension of the scaled font when used to specify
> lengths in the block progression direction."****
>
> ** **
>
> This text is correct, and defines how to interpret the meaning of the 'em'
> unit in accordance to whether it applies in width or height.****
>
>  ****
>
> ** **
>
> One could argue that the first paragraph in 8.2.9 sets up this problem:***
> *
>
> ** **
>
> The tts:fontSize attribute is used to specify a style property that
> defines the font size for glyphs that are selected for glyph areas
> generated by content flowed into a region.****
>
> ** **
>
> Perhaps rewording this to be:****
>
> ** **
>
> The tts:fontSize attribute is used to specify a style property that
> defines the desired font size for selecting and scaling glyphs that are
> selected for glyph areas generated by content flowed into a region. Where
> tts:fontSize is non-anamorphic, i.e. has the same computed value for
> height and width, glyphs should be selected primarily to match as closely
> as possible their height to the computed value, and any scaling should
> preserve the ratio of height to width for each glyph. ****
>
> ** **
>
> I'm not seeing a problem here. Perhaps your misunderstanding came from an
> incorrect association with computed cell size and em square, since I notice
> you didn't quote the language I noted from 6.2.1 above.****
>
>  ****
>
> ** **
>
> would remove the issue?****
>
> ** **
>
> Nigel****
>
> ** **
>
> ** **
>
> On 19/08/2013 14:08, "Glenn Adams" <glenn@skynav.com> wrote:****
>
> ** **
>
> ** **
>
> ** **
>
> On Mon, Aug 19, 2013 at 5:11 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
> wrote:****
>
> Hi Yves, ****
>
> ** **
>
> The draft text for the next edition of the specification, at
> http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-fontSize includes a note
> that hopefully answers your question, as well as making clear that when
> only one length value is specified it applies equally to horizontal and
> vertical scaling, and is proportional to the cell size when specifed as a
> percentage. ****
>
> ** **
>
> The answer to your first question is yes, the width is 640/32 * 75% = 15.*
> ***
>
> ** **
>
> Actually, this is wrong, since it doesn't preserve EM cell aspect ratio.
> If there is one length specification, it applies uniformly to both
> dimensions, however, the resolution of a percentage size is in accordance
> only with the height of a cell (if resolved related to a cell unit).****
>
> ** **
>
> So, for example, if the intrinsic size of an EM square is 1px (width) x
> 1px (height), then your example would scale this EM square to 24px (width)
> x 24px (height).****
>
> ** **
>
> On the other hand, if you specified fontSize="75% 75%", then this would
> scale the EM square to 15px (width) x 24px (height).****
>
> ** **
>
> The relevant spec language is at 8.2.9:****
>
> ** **
>
> If a single <length><https://dvcs.w3.org/hg/ttml/raw-file/default/ttml10/spec/ttaf1-dfxp.html#style-value-length> value
> is specified, then this length applies equally to horizontal and vertical
> scaling of a glyph's EM square; if two <length><https://dvcs.w3.org/hg/ttml/raw-file/default/ttml10/spec/ttaf1-dfxp.html#style-value-length> values
> are specified, then the first expresses the horizontal scaling and the
> second expresses vertical scaling.****
>
>  ****
>
> ** **
>
> Non-proportional scaling is the expected behaviour to allow font sizes
> that are 2 rows in height and 1 column in width to be denoted. ****
>
> ** **
>
> Nigel****
>
> ** **
> ------------------------------
>
> *From:* Nigel Megitt
> *Sent:* 19 August 2013 12:02
> *To:* De Muyter, Yves (Contractor); public-tt@w3.org
> *Subject:* RE: fontSize and percentages****
> ------------------------------
>
> *From:* De Muyter, Yves (Contractor) [Yves.DeMuyter@eu.sony.com]
> *Sent:* 19 August 2013 08:30
> *To:* public-tt@w3.org
> *Subject:* fontSize and percentages****
>
> Hello,****
>
>  ****
>
> I have a question regarding percentages on fontSize and having 1 or 2
> values on the tts:fontSize attribute.****
>
>  ****
>
> Given this example (some unneeded attributes are omitted for readability):
> ****
>
>  ****
>
> <tt tts:extent="640px 480px" ttp:cellResolution="32 15">****
>
> <head>****
>
> <layout>****
>
>                 <region xml:id="r1" tts:fontFamily="monospace"
>  tts:fontSize="75%">****
>
> </layout>****
>
> </head>****
>
> <body>****
>
>                 <div region="r1">****
>
>                                 <p>This is text</p>****
>
>                 </div>****
>
> </body>****
>
> </tt>****
>
>  ****
>
> It means the height of the fontsize is 480/15 * 75% = 24****
>
>  ****
>
> Does it also mean the width of the fontsize is 640/32 * 75% = 15  ?****
>
>  ****
>
> Or does it mean we need to use the scaling value of the height and apply
> that equally to the width to have proportional scaling ? The spec doesn¹t
> clearly say that having a single scaling factor means you need to have
> proportional scaling, that¹s why I¹m hesitating right now for this detail.
> ****
>
>  ****
>
> Yves De Muyter****
>
> Techsoft Centre****
>
> Technology and Software Centre Europe (TSCE)****
>
>  ****
>
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