Fix for Thai characters with a below mark

Some Thai characters with a mark below got drawn under fonts descent
causing them to be clipped in some situations.

Added checking for this and use of lower offset if needed.

Task-Number: ou1cimx1#979179
Change-Id: If9fb643d4dee24342215a637c805d52b78584333
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

3 files changed, 16 insertions, 4 deletions

diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
index af0ee52..48e9064 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
@@ -344,6 +344,11 @@ static inline void positionCluster(HB_ShaperItem *item, int gfrom,  int glast)
 
         }
 
+        // Check drawing below fonts descent
+        if (cmb == HB_Combining_Below || cmb == HB_Combining_BelowRight)
+            if ((markMetrics.height + offset) > item->font->klass->getFontMetric(item->font, HB_FontDescent))
+                offset = markMetrics.y; // Use offset from mark metrics so it won't get drawn below descent
+
         // combining marks of different class don't interact. Reset the rectangle.
         if (cmb != lastCmb) {
             //qDebug("resetting rect");
diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
index 470e27b..b3f5226 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
@@ -231,7 +231,8 @@ typedef struct {
 } HB_GlyphMetrics;
 
 typedef enum {
-    HB_FontAscent
+    HB_FontAscent,
+    HB_FontDescent
 } HB_FontMetric;
 
 typedef struct {
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 0253657..05e4e9e 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -128,11 +128,17 @@ static void hb_getGlyphMetrics(HB_Font font, HB_Glyph glyph, HB_GlyphMetrics *me
 
 static HB_Fixed hb_getFontMetric(HB_Font font, HB_FontMetric metric)
 {
-    if (metric == HB_FontAscent) {
-        QFontEngine *fe = (QFontEngine *)font->userData;
+    QFontEngine *fe = (QFontEngine *)font->userData;
+    switch (metric) {
+    case HB_FontAscent:
         return fe->ascent().value();
+        break;
+    case HB_FontDescent:
+        return fe->descent().value();
+        break;
+    default:
+        return 0;
     }
-    return 0;
 }
 
 HB_Error QFontEngine::getPointInOutline(HB_Glyph glyph, int flags, hb_uint32 point, HB_Fixed *xpos, HB_Fixed *ypos, hb_uint32 *nPoints)