Bug #175108. Crashes when displaying to non-RENDER enabled servers when trying to empty text. Measure all the glyphs before they are passed to the draw functions and if there's nothing but empty glyphs, don't bother drawing.

gfx/src/gtk/nsFontMetricsXft.cpp

@@ -138,7 +138,7 @@ static void GdkRegionSetXftClip(GdkRegion *aGdkRegion, XftDraw *aDraw);
 #define UCS2_NOMAPPING 0xFFFD
 #define UCS2_SPACE 0x0020
 
-static XftCharFontSpec  gFontSpecBuffer[FONT_SPEC_BUFFER_SIZE];
+static XftGlyphFontSpec gFontSpecBuffer[FONT_SPEC_BUFFER_SIZE];
 
 PRLogModuleInfo *gXftFontLoad = nsnull;
 
@@ -547,17 +547,20 @@ nsFontMetricsXft::DrawString(const char *aString, PRUint32 aLength,
 
     // set up our spec buffer
     PRBool useLocalSpecBuffer = PR_FALSE;
-    XftCharFontSpec *specBuffer = gFontSpecBuffer;
+    XftGlyphFontSpec *specBuffer = gFontSpecBuffer;
 
     // see if we have to allocate our own spec buffer
     if (aLength > FONT_SPEC_BUFFER_SIZE) {
         useLocalSpecBuffer = PR_TRUE;
-        specBuffer = new XftCharFontSpec[aLength];
+        specBuffer = new XftGlyphFontSpec[aLength];
 
         if (!specBuffer)
             return NS_ERROR_FAILURE;
     }
 
+    // If we find a glyph that is non-empty, this will be set.
+    PRBool foundGlyph = PR_FALSE;
+
     // our X offset when drawing
     nscoord xOffset = 0;
 
@@ -571,17 +574,29 @@ nsFontMetricsXft::DrawString(const char *aString, PRUint32 aLength,
         // convert this into device coordinates
         aContext->GetTranMatrix()->TransformCoord(&x, &y);
 
-        specBuffer[i].font = mWesternFont->GetXftFont();
-        specBuffer[i].ucs4 = c;
         specBuffer[i].x = x;
         specBuffer[i].y = y;
+        specBuffer[i].font = mWesternFont->GetXftFont();
+        specBuffer[i].glyph = XftCharIndex(GDK_DISPLAY(),
+                                           mWesternFont->GetXftFont(), c);
+
+        // check to see if this glyph is non-empty
+        if (!foundGlyph) {
+            XGlyphInfo info;
+            XftGlyphExtents(GDK_DISPLAY(), specBuffer[i].font,
+                            &specBuffer[i].glyph, 1, &info);
+
+            if (info.width && info.height)
+                foundGlyph = PR_TRUE;
+        }
 
         // bump up our spacing
         xOffset += *aSpacing++;
     }
 
     // go forth and blit!
-    XftDrawCharFontSpec(draw, &color, specBuffer, aLength);
+    if (foundGlyph)
+        XftDrawGlyphFontSpec(draw, &color, specBuffer, aLength);
 
     // only free memory if we didn't use the static buffer
     if (useLocalSpecBuffer)
@@ -611,7 +626,7 @@ nsFontMetricsXft::DrawString(const PRUnichar* aString, PRUint32 aLength,
     // If we've been asked to draw more than the buffer size, allocate
     // a temporary buffer.  This avoids allocations for every draw.
     PRBool useLocalSpecBuffer = PR_FALSE;
-    XftCharFontSpec *specBuffer = gFontSpecBuffer;
+    XftGlyphFontSpec *specBuffer = gFontSpecBuffer;
 
     // The spec buffer length might change if there's a character that
     // we can't render in the middle of the string.  Because of this,
@@ -620,7 +635,7 @@ nsFontMetricsXft::DrawString(const PRUnichar* aString, PRUint32 aLength,
 
     if (aLength > FONT_SPEC_BUFFER_SIZE) {
         useLocalSpecBuffer = PR_TRUE;
-        specBuffer = new XftCharFontSpec[aLength];
+        specBuffer = new XftGlyphFontSpec[aLength];
 
         if (!specBuffer)
             return NS_ERROR_FAILURE;
@@ -629,6 +644,9 @@ nsFontMetricsXft::DrawString(const PRUnichar* aString, PRUint32 aLength,
     float P2T;
     mDeviceContext->GetDevUnitsToAppUnits(P2T);
 
+    // If we find a glyph that is non-empty, this will be set.
+    PRBool foundGlyph = PR_FALSE;
+
     // Set up the mini font, if it hasn't already been done before.
     // If it fails, we'll just substitute the space character below.
 
@@ -690,20 +708,36 @@ nsFontMetricsXft::DrawString(const PRUnichar* aString, PRUint32 aLength,
 
     FoundFont:
         // use current found font to render this character
-        specBuffer[specBufferLen].font = currFont->GetXftFont();
-        specBuffer[specBufferLen].ucs4 = c;
         specBuffer[specBufferLen].x = x;
         specBuffer[specBufferLen].y = y;
+        specBuffer[specBufferLen].font = currFont->GetXftFont();
+        specBuffer[specBufferLen].glyph = XftCharIndex(GDK_DISPLAY(),
+                                                       currFont->GetXftFont(),
+                                                       c);
+
+        // check to see if this glyph is non-empty
+        if (!foundGlyph) {
+            XGlyphInfo info;
+            XftGlyphExtents(GDK_DISPLAY(), specBuffer[specBufferLen].font,
+                            &specBuffer[specBufferLen].glyph,
+                            1, &info);
+
+            if (info.width && info.height)
+                foundGlyph = PR_TRUE;
+        }
+
         ++specBufferLen;
 
         if (aSpacing)
             xOffset += *aSpacing++;
         else
             xOffset += NSToCoordRound(currFont->GetWidth16(&c, 1) * P2T);
+
     }
 
     // Go forth and blit!
-    XftDrawCharFontSpec(draw, &color, specBuffer, specBufferLen);
+    if (foundGlyph)
+        XftDrawGlyphFontSpec(draw, &color, specBuffer, specBufferLen);
 
     // only free memory if we didn't use the static buffer
     if (useLocalSpecBuffer)