WIP: Support Kerning ASS header to force Uniscribe rendering for all text

astiob · astiob · commit f17dca95ba77 · 2024-03-02T22:29:37.000+02:00
This force-enables OpenType shaping (GPOS kerning and GSUB ligatures)
and inline font fallback throughout the text.

The existing behaviour (preserved with Kerning: no) is that TextOut and
GetTextExtentPoint32 automatically enable it in CWords that either contain
non-European scripts (as determined by ScriptIsComplex) or use fonts that
lack European support (as determined by having glyphs for the 4 characters
'd', 'M', 'r', '"'), but this leads to inconsistent and suboptimal output:
  * some words or lines may have kerning while others lack it;
  * font choice may differ when the primary font is missing some glyphs,
    and some words or lines may even show tofu boxes while others show
    glyphs from fallback fonts;
  * line layout is performed using widths computed for each individual
    word, but output is often performed several words at a time: if any
    of the words involved triggers complex script shaping, then the whole
    sequence gains kerning and ligatures, which can change the width
    significantly and cause layout inconsistencies such as right-aligned
    lines being placed too far to the left of the alignment point;
  * kerning and ligatures improve text display quality, but subtitle
    authors have no sane way to enable them in European languages;
  * libass currently unconditionally displays ligatures and performs
    font fallback and supports kerning with the Kerning header,
    but VSFilter provides no sane way to achieve the same output.

While we have the chance, also disable (avoid enabling) some legacy
compatibility features concerning bidirectional text and localized digits
when Kerning: yes. This provides more standards-compliant output
and better matches libass's current output.

In a separate commit, bidirectional pair matching may also be enabled
in coordination with libass: to do this, ScriptStringAnalyse simply needs
to be passed a SCRIPT_CONTROL instance with fUseStandardBidi = 1.
diff --git a/src/subtitles/RTS.cpp b/src/subtitles/RTS.cpp
@@ -666,6 +666,33 @@ bool CText::CreatePath(PathData* path_data)
             width += extent.cx + (int)m_style.get().fontSpacing;
         }
     }
+    else if(m_style.get().fGlyphShaping)
+    {
+        succeeded = path_data->BeginPath(g_hDC);
+        if(!succeeded)
+        {
+            SelectFont(g_hDC, hOldFont); ASSERT(0); return(false);
+        }
+        SCRIPT_STRING_ANALYSIS ssa;
+        HRESULT hr = ScriptStringAnalyse(g_hDC, str, str.GetLength(),
+            0, -1, SSA_GLYPHS | SSA_FALLBACK | SSA_LINK,
+            -1, NULL, NULL, NULL, NULL, NULL, &ssa);
+        if(FAILED(hr))
+        {
+            SelectFont(g_hDC, hOldFont); ASSERT(0); return(false);
+        }
+        hr = ScriptStringOut(ssa, 0, 0, 0, NULL, 0, 0, FALSE);
+        ScriptStringFree(&ssa);
+        if(FAILED(hr))
+        {
+            SelectFont(g_hDC, hOldFont); ASSERT(0); return(false);
+        }
+        succeeded = path_data->EndPath(g_hDC);
+        if(!succeeded)
+        {
+            SelectFont(g_hDC, hOldFont); ASSERT(0); return(false);
+        }
+    }
     else
     {
         CSize extent;
@@ -712,6 +739,18 @@ void CText::GetTextInfo(TextInfo *output, const FwSTSStyle& style, const CString
         }
         //          m_width -= (int)m_style.get().fontSpacing; // TODO: subtract only at the end of the line
     }
+    else if(style.get().fGlyphShaping)
+    {
+        SCRIPT_STRING_ANALYSIS ssa;
+        HRESULT hr = ScriptStringAnalyse(g_hDC, str, str.GetLength(),
+            0, -1, SSA_GLYPHS | SSA_FALLBACK | SSA_LINK,
+            -1, NULL, NULL, NULL, NULL, NULL, &ssa);
+        if(FAILED(hr)) {SelectFont(g_hDC, hOldFont); ASSERT(0); return;}
+        const SIZE *pSize = ScriptString_pSize(ssa);
+        if(pSize) output->m_width += pSize->cx;
+        ScriptStringFree(&ssa);
+        if(!pSize) {SelectFont(g_hDC, hOldFont); ASSERT(0); return;}
+    }
     else
     {
         CSize extent;
@@ -2959,6 +2998,7 @@ CSubtitle* CRenderedTextSubtitle::GetSubtitle(int entry)
         tmp.outlineWidthY *= (m_fScaledBAS ? sub->m_scaley : 1) * MAX_SUB_PIXEL;
         tmp.shadowDepthX  *= (m_fScaledBAS ? sub->m_scalex : 1) * MAX_SUB_PIXEL;
         tmp.shadowDepthY  *= (m_fScaledBAS ? sub->m_scaley : 1) * MAX_SUB_PIXEL;
+        tmp.fGlyphShaping |= m_fKerning;
         FwSTSStyle fw_tmp(tmp);
         if(m_nPolygon)
         {
diff --git a/src/subtitles/STS.cpp b/src/subtitles/STS.cpp
@@ -2096,6 +2096,12 @@ if(sver <= 4)   style->scrAlignment = (style->scrAlignment&4) ? ((style->scrAlig
             buff.MakeLower();
             ret.m_fScaledBAS = buff.Find(L"yes") >= 0;
         }
+        else if(entry == L"kerning")
+        {
+            buff = GetStr(buff);
+            buff.MakeLower();
+            ret.m_fKerning = buff.Find(L"yes") >= 0;
+        }
         else if(entry == L"[v4 styles]")
         {
             fRet = true;
@@ -3643,6 +3649,7 @@ void STSStyle::SetDefault()
     fontAngleX    = 
     fontAngleY    = 0;
     relativeTo    = 2;
+    fGlyphShaping = false;
 }
 
 bool STSStyle::operator == (const STSStyle& s) const
diff --git a/src/subtitles/STS.h b/src/subtitles/STS.h
@@ -78,6 +78,9 @@ struct STSStyle: public STSStyleBase
     int      relativeTo;   // 0: window, 1: video, 2: undefined (~window)
                            // Edit: NOT supported now
 
+    bool     fGlyphShaping;  // whether to force-enable complex script shaping
+                             // including kerning, ligatures and font fallback
+
     STSStyle();
 
     void SetDefault();
@@ -180,6 +183,7 @@ class CSimpleTextSubtitle
     int            m_defaultWrapStyle;
     int            m_collisions;
     bool           m_fScaledBAS;
+    bool           m_fKerning;
     CSize          m_layout_size;
 
     CSTSStyleMap   m_styles;

Original file line number	Diff line number	Diff line change
`@@ -2096,6 +2096,12 @@ if(sver <= 4) style->scrAlignment = (style->scrAlignment&4) ? ((style->scrAlig`
`2096`	`2096`	`buff.MakeLower();`
`2097`	`2097`	`ret.m_fScaledBAS = buff.Find(L"yes") >= 0;`
`2098`	`2098`	`}`
	`2099`	`+ else if(entry == L"kerning")`
	`2100`	`+ {`
	`2101`	`+ buff = GetStr(buff);`
	`2102`	`+ buff.MakeLower();`
	`2103`	`+ ret.m_fKerning = buff.Find(L"yes") >= 0;`
	`2104`	`+ }`
`2099`	`2105`	`else if(entry == L"[v4 styles]")`
`2100`	`2106`	`{`
`2101`	`2107`	`fRet = true;`
`@@ -3643,6 +3649,7 @@ void STSStyle::SetDefault()`
`3643`	`3649`	`fontAngleX =`
`3644`	`3650`	`fontAngleY = 0;`
`3645`	`3651`	`relativeTo = 2;`
	`3652`	`+ fGlyphShaping = false;`
`3646`	`3653`	`}`
`3647`	`3654`
`3648`	`3655`	`bool STSStyle::operator == (const STSStyle& s) const`