DWrite: More accurate glyph paths for small fonts

Applying a transformation matrix to a glyph path after converting
floats to fixed point numbers caused caluculation errors. Apply the
transform before the conversion.

Fixes cairo/cairo#611

1 files changed, 37 insertions, 29 deletions

diff --git a/src/win32/cairo-dwrite-font.cpp b/src/win32/cairo-dwrite-font.cpp
index 1d84fc047..8346e4856 100644
--- a/src/win32/cairo-dwrite-font.cpp
+++ b/src/win32/cairo-dwrite-font.cpp
@@ -736,8 +736,9 @@ _cairo_dwrite_scaled_font_init_glyph_metrics(cairo_dwrite_scaled_font_t *scaled_
 class GeometryRecorder : public IDWriteGeometrySink
 {
 public:
-    GeometryRecorder(cairo_path_fixed_t *aCairoPath)
-	: mCairoPath(aCairoPath) {}
+    GeometryRecorder(cairo_path_fixed_t *aCairoPath, const cairo_matrix_t &matrix)
+	: mCairoPath(aCairoPath)
+	, mMatrix(matrix) {}
 
     // IUnknown interface
     IFACEMETHOD(QueryInterface)(IID const& iid, OUT void** ppObject)
@@ -779,10 +780,14 @@ public:
 	D2D1_POINT_2F startPoint,
 	D2D1_FIGURE_BEGIN figureBegin)
     {
-	mStartPoint = startPoint;
+	double x = startPoint.x;
+	double y = startPoint.y;
+	cairo_matrix_transform_point(&mMatrix, &x, &y);
+	mStartPointX = _cairo_fixed_from_double(x);
+	mStartPointY = _cairo_fixed_from_double(y);
 	cairo_status_t status = _cairo_path_fixed_move_to(mCairoPath,
-							  _cairo_fixed_from_double(startPoint.x),
-							  _cairo_fixed_from_double(startPoint.y));
+							  mStartPointX,
+							  mStartPointY);
 	(void)status; /* squelch warning */
     }
 
@@ -791,8 +796,8 @@ public:
     {
 	if (figureEnd == D2D1_FIGURE_END_CLOSED) {
 	    cairo_status_t status = _cairo_path_fixed_line_to(mCairoPath,
-							      _cairo_fixed_from_double(mStartPoint.x),
-							      _cairo_fixed_from_double(mStartPoint.y));
+							      mStartPointX,
+							      mStartPointY);
 	    (void)status; /* squelch warning */
 	}
     }
@@ -802,13 +807,22 @@ public:
 	UINT beziersCount)
     {
 	for (unsigned int i = 0; i < beziersCount; i++) {
+	    double x1 = beziers[i].point1.x;
+	    double y1 = beziers[i].point1.y;
+	    double x2 = beziers[i].point2.x;
+	    double y2 = beziers[i].point2.y;
+	    double x3 = beziers[i].point3.x;
+	    double y3 = beziers[i].point3.y;
+	    cairo_matrix_transform_point(&mMatrix, &x1, &y1);
+	    cairo_matrix_transform_point(&mMatrix, &x2, &y2);
+	    cairo_matrix_transform_point(&mMatrix, &x3, &y3);
 	    cairo_status_t status = _cairo_path_fixed_curve_to(mCairoPath,
-							       _cairo_fixed_from_double(beziers[i].point1.x),
-							       _cairo_fixed_from_double(beziers[i].point1.y),
-							       _cairo_fixed_from_double(beziers[i].point2.x),
-							       _cairo_fixed_from_double(beziers[i].point2.y),
-							       _cairo_fixed_from_double(beziers[i].point3.x),
-							       _cairo_fixed_from_double(beziers[i].point3.y));
+							       _cairo_fixed_from_double(x1),
+							       _cairo_fixed_from_double(y1),
+							       _cairo_fixed_from_double(x2),
+							       _cairo_fixed_from_double(y2),
+							       _cairo_fixed_from_double(x3),
+							       _cairo_fixed_from_double(y3));
 	    (void)status; /* squelch warning */
 	}
     }
@@ -818,16 +832,21 @@ public:
 	UINT pointsCount)
     {
 	for (unsigned int i = 0; i < pointsCount; i++) {
+	    double x = points[i].x;
+	    double y = points[i].y;
+	    cairo_matrix_transform_point(&mMatrix, &x, &y);
 	    cairo_status_t status = _cairo_path_fixed_line_to(mCairoPath,
-							      _cairo_fixed_from_double(points[i].x),
-							      _cairo_fixed_from_double(points[i].y));
+							      _cairo_fixed_from_double(x),
+							      _cairo_fixed_from_double(y));
 	    (void)status; /* squelch warning */
 	}
     }
 
 private:
     cairo_path_fixed_t *mCairoPath;
-    D2D1_POINT_2F mStartPoint;
+    const cairo_matrix_t &mMatrix;
+    cairo_fixed_t mStartPointX;
+    cairo_fixed_t mStartPointY;
 };
 
 static cairo_int_status_t
@@ -837,7 +856,7 @@ _cairo_dwrite_scaled_font_init_glyph_path(cairo_dwrite_scaled_font_t *scaled_fon
     cairo_int_status_t status;
     cairo_path_fixed_t *path;
     path = _cairo_path_fixed_create();
-    GeometryRecorder recorder(path);
+    GeometryRecorder recorder(path, scaled_font->base.scale);
 
     DWRITE_GLYPH_OFFSET offset;
     offset.advanceOffset = 0;
@@ -846,12 +865,7 @@ _cairo_dwrite_scaled_font_init_glyph_path(cairo_dwrite_scaled_font_t *scaled_fon
     FLOAT advance = 0.0;
     cairo_dwrite_font_face_t *dwriteff = (cairo_dwrite_font_face_t*)scaled_font->base.font_face;
 
-    /* GetGlyphRunOutline seems to ignore hinting so just use the em size to get the outline
-     * to avoid rounding errors when converting to cairo_path_fixed_t.
-     */
-    DWRITE_FONT_METRICS metrics;
-    dwriteff->dwriteface->GetMetrics(&metrics);
-    HRESULT hr = dwriteff->dwriteface->GetGlyphRunOutline(metrics.designUnitsPerEm,
+    HRESULT hr = dwriteff->dwriteface->GetGlyphRunOutline(1,
 							  &glyphId,
 							  &advance,
 							  &offset,
@@ -864,12 +878,6 @@ _cairo_dwrite_scaled_font_init_glyph_path(cairo_dwrite_scaled_font_t *scaled_fon
 
     status = (cairo_int_status_t)_cairo_path_fixed_close_path(path);
 
-    /* Now scale the em size down to 1.0 and apply the font matrix and font ctm. */
-    cairo_matrix_t mat = scaled_font->base.ctm;
-    cairo_matrix_multiply(&mat, &scaled_font->base.font_matrix, &mat);
-    cairo_matrix_scale (&mat, 1.0/metrics.designUnitsPerEm, 1.0/metrics.designUnitsPerEm);
-    _cairo_path_fixed_transform(path, &mat);
-
     _cairo_scaled_glyph_set_path (scaled_glyph,
 				  &scaled_font->base,
 				  path);