Round scale to nearest 26.6 fixed point.

CONTRIBUTORS

@@ -27,6 +27,7 @@
 # Please keep the list sorted.
 
 Andrew Gerrand <[email protected]>
+Dmitri Shuralyov <[email protected]>
 Jeff R. Allen <[email protected]> <[email protected]>
 Maksim Kochkin <[email protected]>
 Michael Fogleman <[email protected]>

freetype.go

@@ -78,7 +78,7 @@ type Context struct {
 // PointToFixed converts the given number of points (as in "a 12 point font")
 // into a 26.6 fixed point number of pixels.
 func (c *Context) PointToFixed(x float64) fixed.Int26_6 {
-	return fixed.Int26_6(x * float64(c.dpi) * (64.0 / 72.0))
+	return fixed.Int26_6(0.5 + (x * c.dpi * 64 / 72))
 }
 
 // drawContour draws the given closed contour with the given offset.
@@ -260,7 +260,7 @@ func (c *Context) DrawString(s string, p fixed.Point26_6) (fixed.Point26_6, erro
 // recalc recalculates scale and bounds values from the font size, screen
 // resolution and font metrics, and invalidates the glyph cache.
 func (c *Context) recalc() {
-	c.scale = fixed.Int26_6(c.fontSize * c.dpi * (64.0 / 72.0))
+	c.scale = fixed.Int26_6(0.5 + (c.fontSize * c.dpi * 64 / 72))
 	if c.f == nil {
 		c.r.SetBounds(0, 0)
 	} else {

freetype_test.go

@@ -12,6 +12,8 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+
+	"golang.org/x/image/math/fixed"
 )
 
 func BenchmarkDrawString(b *testing.B) {
@@ -57,3 +59,26 @@ func BenchmarkDrawString(b *testing.B) {
 	mallocs = ms.Mallocs - mallocs
 	b.Logf("%d iterations, %d mallocs per iteration\n", b.N, int(mallocs)/b.N)
 }
+
+func TestScaling(t *testing.T) {
+	c := NewContext()
+	for _, tc := range [...]struct {
+		in   float64
+		want fixed.Int26_6
+	}{
+		{in: 12, want: fixed.I(12)},
+		{in: 11.992, want: fixed.I(12) - 1},
+		{in: 11.993, want: fixed.I(12)},
+		{in: 12.007, want: fixed.I(12)},
+		{in: 12.008, want: fixed.I(12) + 1},
+		{in: 86.4, want: fixed.Int26_6(86<<6 + 26)}, // Issue https://github.com/golang/freetype/issues/85.
+	} {
+		c.SetFontSize(tc.in)
+		if got, want := c.scale, tc.want; got != want {
+			t.Errorf("scale after SetFontSize(%v) = %v, want %v", tc.in, got, want)
+		}
+		if got, want := c.PointToFixed(tc.in), tc.want; got != want {
+			t.Errorf("PointToFixed(%v) = %v, want %v", tc.in, got, want)
+		}
+	}
+}