tdf#93884 windows opengl: make space around cached glyphs depend on font size

Cached glyphs used to have a 2px border in all font sizes, that's too
small for larger fonts. Make the border size depend on the font size for
larger fonts to make sure that the rendered glyphs are indeed
independent.  The introduced GLYPH_SPACE_RATIO = 8 constant is the
smallest value where I don't see overflows anymore for large fonts.

With this, not even the bugdoc renders correctly when presenting, but
also the text is OK when the font size is set to the max allowed by the
UI (96pt).

Change-Id: I52aa5c4444583fc0467291463697a63f2b8fc86c

1 files changed, 39 insertions, 20 deletions

diff --git a/vcl/win/source/gdi/winlayout.cxx b/vcl/win/source/gdi/winlayout.cxx
index 6fc12454e9d8..200c4eea9320 100644
--- a/vcl/win/source/gdi/winlayout.cxx
+++ b/vcl/win/source/gdi/winlayout.cxx
@@ -59,6 +59,14 @@ typedef std::unordered_map<int,int> IntMap;
 
 #include <config_mingw.h>
 
+namespace
+{
+// Extra space at the top and bottom of the glyph in total = tmHeight / GLYPH_SPACE_RATIO;
+const int GLYPH_SPACE_RATIO = 8;
+// Border size at the top of the glyph = tmHeight / GLYPH_OFFSET_RATIO;
+const int GLYPH_OFFSET_RATIO = GLYPH_SPACE_RATIO * 2;
+}
+
 struct OpenGLGlyphCacheChunk
 {
     WORD mnFirstGlyph;
@@ -66,7 +74,18 @@ struct OpenGLGlyphCacheChunk
     std::vector<Rectangle> maLocation;
     std::shared_ptr<OpenGLTexture> mpTexture;
     int mnAscent;
+    int mnHeight;
     bool mbVertical;
+
+    int getExtraSpace() const
+    {
+        return std::max(mnHeight / GLYPH_SPACE_RATIO, 4);
+    }
+
+    int getExtraOffset() const
+    {
+        return std::max(mnHeight / GLYPH_OFFSET_RATIO, 2);
+    }
 };
 
 // win32 specific physical font instance
@@ -278,10 +297,21 @@ bool ImplWinFontEntry::AddChunkOfGlyphs(int nGlyphIndex, const WinLayout& rLayou
         sLine << aABC[i].abcA << ":" << aABC[i].abcB << ":" << aABC[i].abcC << " ";
     SAL_INFO("vcl.gdi.opengl", "ABC widths: " << sLine.str());
 
+    TEXTMETRICW aTextMetric;
+    if (!GetTextMetricsW(hDC, &aTextMetric))
+    {
+        SAL_WARN("vcl.gdi", "GetTextMetrics failed: " << WindowsErrorString(GetLastError()));
+        SelectObject(hDC, hOrigFont);
+        DeleteDC(hDC);
+        return false;
+    }
+    aChunk.mnAscent = aTextMetric.tmAscent;
+    aChunk.mnHeight = aTextMetric.tmHeight;
+
     // Try hard to avoid overlap as we want to be able to use
     // individual rectangles for each glyph. The ABC widths don't
     // take anti-alising into consideration. Let's hope that leaving
-    // four pixels of "extra" space inbetween glyphs will help.
+    // "extra" space inbetween glyphs will help.
     std::vector<int> aDX(nCount);
     int totWidth = 0;
     for (int i = 0; i < nCount; i++)
@@ -291,20 +321,10 @@ bool ImplWinFontEntry::AddChunkOfGlyphs(int nGlyphIndex, const WinLayout& rLayou
             aDX[0] += std::abs(aABC[0].abcA);
         if (i < nCount-1)
             aDX[i] += std::abs(aABC[i+1].abcA);
-        aDX[i] += 4;
+        aDX[i] += aChunk.getExtraSpace();
         totWidth += aDX[i];
     }
 
-    TEXTMETRICW aTextMetric;
-    if (!GetTextMetricsW(hDC, &aTextMetric))
-    {
-        SAL_WARN("vcl.gdi", "GetTextMetrics failed: " << WindowsErrorString(GetLastError()));
-        SelectObject(hDC, hOrigFont);
-        DeleteDC(hDC);
-        return false;
-    }
-    aChunk.mnAscent = aTextMetric.tmAscent;
-
     LOGFONTW aLogfont;
     if (!GetObjectW(rLayout.mhFont, sizeof(aLogfont), &aLogfont))
     {
@@ -336,18 +356,18 @@ bool ImplWinFontEntry::AddChunkOfGlyphs(int nGlyphIndex, const WinLayout& rLayou
     if (!DeleteDC(hDC))
         SAL_WARN("vcl.gdi", "DeleteDC failed: " << WindowsErrorString(GetLastError()));
 
-    // Leave two pixels of extra space also at top and bottom
+    // Leave extra space also at top and bottom
     int nBitmapWidth, nBitmapHeight;
     if (sFaceName[0] == '@')
     {
-        nBitmapWidth = aSize.cy + 4;
+        nBitmapWidth = aSize.cy + aChunk.getExtraSpace();
         nBitmapHeight = totWidth;
         aChunk.mbVertical = true;
     }
     else
     {
         nBitmapWidth = totWidth;
-        nBitmapHeight = aSize.cy + 4;
+        nBitmapHeight = aSize.cy + aChunk.getExtraSpace();
         aChunk.mbVertical = false;
     }
 
@@ -384,9 +404,8 @@ bool ImplWinFontEntry::AddChunkOfGlyphs(int nGlyphIndex, const WinLayout& rLayou
 
     aDC.fill(MAKE_SALCOLOR(0xff, 0xff, 0xff));
 
-    // The 2,2 is for the extra space
-    int nY = 2;
-    int nX = 2;
+    int nY =  aChunk.getExtraOffset();
+    int nX =  nY;
     if (aChunk.mbVertical)
         nX += aDX[0];
     if (!ExtTextOutW(aDC.getCompatibleHDC(), nX, nY, ETO_GLYPH_INDEX, NULL, aGlyphIndices.data(), nCount, aDX.data()))
@@ -416,7 +435,7 @@ bool ImplWinFontEntry::AddChunkOfGlyphs(int nGlyphIndex, const WinLayout& rLayou
             aChunk.maLocation[i].Right() = nPos + aDX[i];
             nPos = aChunk.maLocation[i].Right();
             aChunk.maLocation[i].Top() = 0;
-            aChunk.maLocation[i].Bottom() = aSize.cy + 4;
+            aChunk.maLocation[i].Bottom() = aSize.cy + aChunk.getExtraSpace();
         }
     }
 
@@ -1761,7 +1780,7 @@ bool UniscribeLayout::DrawCachedGlyphs(SalGraphics& rGraphics) const
             {
                 SalTwoRect a2Rects(rChunk.maLocation[n].Left(), rChunk.maLocation[n].Top(),
                                    rChunk.maLocation[n].getWidth(), rChunk.maLocation[n].getHeight(),
-                                   nAdvance + aPos.X() + mpGlyphOffsets[i].du - 2, aPos.Y() + mpGlyphOffsets[i].dv - rChunk.mnAscent - 2,
+                                   nAdvance + aPos.X() + mpGlyphOffsets[i].du - rChunk.getExtraOffset(), aPos.Y() + mpGlyphOffsets[i].dv - rChunk.mnAscent - rChunk.getExtraOffset(),
                                    rChunk.maLocation[n].getWidth(), rChunk.maLocation[n].getHeight()); // ???
                 pImpl->DrawMask(*rChunk.mpTexture, salColor, a2Rects);
             }