rbs Reporter
	Description • 23 years ago

The fix for bug 20394 (and related) requires the support of the following
methods in the nsIRenderingContext API.
============================================================================
  NS_IMETHOD
  GetDimensions(const char* aString, PRUint32 aLength,
                nsDimensions& aDimensions) = 0;
  NS_IMETHOD
  GetDimensions(const PRUnichar* aString, PRUint32 aLength,
                nsDimensions& aDimensions, PRInt32* aFontID = nsnull) = 0;

nsDimensions is the struct to fill. It is described below. Basically, since
font-switching may arise when rendering a piece of (i18n) Unicode string, 
what is needed is to also return the max ascent and max descent of all
the fonts involved. 

For a string in ASCII, there is no font-switching and thus:
  GetDimensions(const char* aString, ...)
  is:
    aDimensions.width = GetWidth(aString) with the current font
    aDimensions.ascent = the current font's ascent
    aDimensions.descent = the current font's descent

For a string in Unicode, font-switching may arise and thus:
  GetDimensions(const PRUnichar* aString, ...)
  is:
    while (font-switching) {
      aDimensions.width += GetWidth(substring) with the current font
      aDimensions.ascent = max{aDimensions.ascent, current font's ascent}
      aDimensions.descent = max{aDimensions.descent, current font's descent}
    }

This is basically what is needed, but it has to be in the dialect expected
by each platform :-(

Together with these, two trivial methods DrawString2(ASCII/Unicode) are also
needed. Unlike DrawString(), these new methods will draw a string without 
tampering with the aY parameter supplied by the caller. They are aimed at 
allowing to draw muliple piece of string from different fonts in separate calls, 
yet while still keeping them baseline-aligned. The DrawString2() are obtained 
from DrawString() in a trivial manner and it is anticipated that they will 
replace DrawString() once the switch to GetDimensions() is over and callers 
fixed.

An example of a patch to hook GetDimensions() is attached to bug 95721:
http://bugzilla.mozilla.org/showattachment.cgi?attach_id=46317

This bug is currently blocking my font changes that could potentially solve:
 - bug 30910 - Pref for minimum font size
 - bug 32536 - text gets wrong font size 
 - bug 61883 - Smarter default prefs for the 5 basic CSS fonts 
 - bug 74186 - Unable to choose different size for serif and sans-serif fonts 
 - bug 96535 - Font sizes too large for Japanese UI 

(and perhaps other bugs as well, and despite the intensive testing, introduce a 
few regressions of its own, in all fairness -- there is no denying the software 
life cycle :-)

============================================================================
/* Struct used to represent the overall extent of a string
   whose rendering may involve switching between different
   fonts that have different metrics.
*/
struct nsDimensions {
  // max ascent amongst all the fonts needed to represent the string
  nscoord ascent;

  // max descent amongst all the fonts needed to represent the string
  nscoord descent;

  // width of the string
  nscoord width;


  nsDimensions()
  {
    Clear();
  }

  /* Set all member data to zero */
  void 
  Clear() {
    ascent = descent = width = 0;
  }

  /* Append another dimension */
  void 
  operator += (const nsDimensions& aOther) {
    if (ascent < aOther.ascent) ascent = aOther.ascent;
    if (descent < aOther.descent) descent = aOther.descent;   
    width += aOther.width;
  }
};

	rbs Reporter
	Comment 3 • 23 years ago

The above patches (together with those recently checked in for OS/2 and BeoS) 
should bring the ports back in the loop, or at least provide enough head start
to plaform gurus to fix typos. I haven't touched Motif because it seems to be 
there only for historical reasons. I mostly saw empty stubs checked in there 
since 1999.

	rbs Reporter
	Comment 4 • 23 years ago

I have checked-in the two patches listed above.

	rbs Reporter
	Comment 5 • 23 years ago

With the recent fix for GfxMac in bug 100868, the three main platforms are now
in parity. Only postscript printing (GfxPS) remains missing.

	Kevin McCluskey (gone)
	Comment 6 • 23 years ago

Re-assigning to dcone

	Vedran Miletic
	Comment 7 • 21 years ago

retargeting

	Simon Paquet [:sipaq]
	Comment 8 • 21 years ago

Not a blocker.

	Zack Weinberg (:zwol)
	Comment 9 • 13 years ago

The need for this internal change has long since been obviated by other internal changes.