Fix font rendering issues because of an incorrect transform.

This regressed in https://pdfium.googlesource.com/pdfium/+/71c24b839498fb89184002ed30fcff353e1e402c. The code would reach into FreeType internals and reset transform_flags. This would effectively set the font's transform matrix to the identity (since a transform is only used if the flag is set). I removed it because I assumed this is only a cache, and any other place that would call FT_Load_Glyph would have set a transform first. Apparently that's not the case (verified through adding some additional code). The fix is to reset the transform matrix after changing it. This is functionally equivalent to the previous behavior, since if the flag was 0 but there was a transform, it would be ignored until another transform is set.

BUG=479434
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1163423005.

1 files changed, 37 insertions, 4 deletions

diff --git a/core/src/fxge/ge/fx_ge_text.cpp b/core/src/fxge/ge/fx_ge_text.cpp
index 1cdf5b2ef3..88eeb47218 100644
--- a/core/src/fxge/ge/fx_ge_text.cpp
+++ b/core/src/fxge/ge/fx_ge_text.cpp
@@ -12,6 +12,37 @@
 #undef FX_GAMMA_INVERSE
 #define FX_GAMMA(value)			(value)
 #define FX_GAMMA_INVERSE(value)	(value)
+
+namespace {
+
+void ResetTransform(FT_Face face) {
+    FXFT_Matrix  matrix;
+    matrix.xx = 0x10000L;
+    matrix.xy = 0;
+    matrix.yx = 0;
+    matrix.yy = 0x10000L;
+    FXFT_Set_Transform(face, &matrix, 0);
+}
+
+// Sets the given transform on the font, and resets it to the identity when it
+// goes out of scope.
+class ScopedFontTransform
+{
+public:
+    ScopedFontTransform(FT_Face face, FXFT_Matrix* matrix) : m_Face(face) {
+        FXFT_Set_Transform(m_Face, matrix, 0);
+    }
+
+    ~ScopedFontTransform() {
+        ResetTransform(m_Face);
+    }
+
+private:
+    FT_Face m_Face;
+};
+
+}
+
 FX_RECT FXGE_GetGlyphsBBox(FXTEXT_GLYPHPOS* pGlyphAndPos, int nChars, int anti_alias, FX_FLOAT retinaScaleX, FX_FLOAT retinaScaleY)
 {
     FX_RECT rect(0, 0, 0, 0);
@@ -1312,7 +1343,7 @@ CFX_GlyphBitmap* CFX_FaceCache::RenderGlyph(CFX_Font* pFont, FX_DWORD glyph_inde
             pFont->AdjustMMParams(glyph_index, dest_width, pFont->GetSubstFont()->m_Weight);
         }
     }
-    FXFT_Set_Transform(m_Face, &ft_matrix, 0);
+    ScopedFontTransform scoped_transform(m_Face, &ft_matrix);
     int load_flags = (m_Face->face_flags & FT_FACE_FLAG_SFNT) ? FXFT_LOAD_NO_BITMAP : (FXFT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING);
     int error = FXFT_Load_Glyph(m_Face, glyph_index, load_flags);
     if (error) {
@@ -1456,6 +1487,8 @@ FX_BOOL OutputText(void* dib, int x, int y, CFX_Font* pFont, double font_size,
                      glyph_index, argb);
         x_pos += (FX_FLOAT)w / em;
     }
+    if (pText_matrix)
+        ResetTransform(face);
     return TRUE;
 }
 FX_BOOL OutputGlyph(void* dib, int x, int y, CFX_Font* pFont, double font_size,
@@ -1472,7 +1505,7 @@ FX_BOOL OutputGlyph(void* dib, int x, int y, CFX_Font* pFont, double font_size,
         ft_matrix.xy = ft_matrix.yx = 0;
         ft_matrix.yy = (signed long)(font_size / 64 * 65536);
     }
-    FXFT_Set_Transform(pFont->m_Face, &ft_matrix, 0);
+    ScopedFontTransform scoped_transform(pFont->m_Face, &ft_matrix);
     FX_BOOL ret = _OutputGlyph(dib, x, y, pFont,
                                glyph_index, argb);
     return ret;
@@ -1621,8 +1654,8 @@ CFX_PathData* CFX_Font::LoadGlyphPath(FX_DWORD glyph_index, int dest_width)
             AdjustMMParams(glyph_index, dest_width, m_pSubstFont->m_Weight);
         }
     }
-    FXFT_Set_Transform(m_Face, &ft_matrix, 0);
-    int load_flags = (m_Face->face_flags & FT_FACE_FLAG_SFNT) ? FXFT_LOAD_NO_BITMAP : FXFT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING;      
+    ScopedFontTransform scoped_transform(m_Face, &ft_matrix);
+    int load_flags = (m_Face->face_flags & FT_FACE_FLAG_SFNT) ? FXFT_LOAD_NO_BITMAP : FXFT_LOAD_NO_BITMAP | FT_LOAD_NO_HINTING;
     int error = FXFT_Load_Glyph(m_Face, glyph_index, load_flags);
     if (error) {
         return NULL;