JBR-1761 Printing a comment block in landscape mode results in oddly rotated italic letters

Author: JB-Dmitry

src/java.desktop/share/native/libfontmanager/freetypeScaler.c

@@ -662,16 +662,40 @@ static void setupLoadRenderFlags(FTScalerContext *context, int fcHintStyle, FcBo
 }
 #endif
 
+// values used by FreeType (as of version 2.10.1) for italics transformation matrix in FT_GlyphSlot_Oblique
+#define FT_MATRIX_ONE 0x10000
+#define FT_MATRIX_OBLIQUE_XY 0x0366A
+
+static void setupTransform(FT_Matrix* target, FTScalerContext *context) {
+    FT_Matrix* transform = &context->transform;
+    if (context->doItalize) {
+        // we cannot use FT_GlyphSlot_Oblique as it doesn't work well with arbitrary transforms,
+        // so we add corresponding shear transform to the requested glyph transformation
+        target->xx = FT_MATRIX_ONE;
+        target->xy = FT_MATRIX_OBLIQUE_XY;
+        target->yx = 0;
+        target->yy = FT_MATRIX_ONE;
+        FT_Matrix_Multiply(transform, target);
+    } else {
+        target->xx = transform->xx;
+        target->xy = transform->xy;
+        target->yx = transform->yx;
+        target->yy = transform->yy;
+    }
+}
+
 static int setupFTContext(JNIEnv *env, jobject font2D, FTScalerInfo *scalerInfo, FTScalerContext *context,
                           FT_Bool configureFont) {
+    FT_Matrix matrix;
     int errCode = 0;
     scalerInfo->env = env;
     scalerInfo->font2D = font2D;
 
     if (context != NULL) {
-        FT_UInt dpi = (FT_UInt) getScreenResolution(env);
-        FT_Set_Transform(scalerInfo->face, &context->transform, NULL);
+        setupTransform(&matrix, context);
+        FT_Set_Transform(scalerInfo->face, &matrix, NULL);
 
+        FT_UInt dpi = (FT_UInt) getScreenResolution(env);
         errCode = FT_Set_Char_Size(scalerInfo->face, 0, ADJUST_FONT_SIZE(context->ptsz, dpi), dpi, dpi);
         if (errCode) return errCode;
 
@@ -869,11 +893,8 @@ static int setupFTContext(JNIEnv *env, jobject font2D, FTScalerInfo *scalerInfo,
     return 0;
 }
 
-/* ftsynth.c uses (0x10000, 0x0366A, 0x0, 0x10000) matrix to get oblique
-   outline.  Therefore x coordinate will change by 0x0366A*y.
-   Note that y coordinate does not change. These values are based on
-   libfreetype version 2.9.1. */
-#define OBLIQUE_MODIFIER(y)  (context->doItalize ? ((y)*0x366A/0x10000) : 0)
+// using same values as for the transformation matrix
+#define OBLIQUE_MODIFIER(y)  (context->doItalize ? ((y)*FT_MATRIX_OBLIQUE_XY/FT_MATRIX_ONE) : 0)
 
 /* FT_GlyphSlot_Embolden (ftsynth.c) uses FT_MulFix(units_per_EM, y_scale) / 24
  * strength value when glyph format is FT_GLYPH_FORMAT_OUTLINE. This value has
@@ -1242,9 +1263,6 @@ Java_sun_font_FreetypeFontScaler_getGlyphImageNative(
     if (context->doBold) { /* if bold style */
         FT_GlyphSlot_Embolden(ftglyph);
     }
-    if (context->doItalize) { /* if oblique */
-        FT_GlyphSlot_Oblique(ftglyph);
-    }
 
     /* generate bitmap if it is not done yet
      e.g. if algorithmic styling is performed and style was added to outline */
@@ -1470,9 +1488,6 @@ static FT_Outline* getFTOutline(JNIEnv* env, jobject font2D,
     if (context->doBold) { /* if bold style */
         FT_GlyphSlot_Embolden(ftglyph);
     }
-    if (context->doItalize) { /* if oblique */
-        FT_GlyphSlot_Oblique(ftglyph);
-    }
 
     FT_Outline_Translate(&ftglyph->outline,
                          FloatToF26Dot6(xpos),