draw: add a test for src translation invariance.
Change-Id: Iedd4cc4e2b88c5fa9e4fcd547756588e4d87bfff
Reviewed-on: https://go-review.googlesource.com/7471
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/draw/scale_test.go b/draw/scale_test.go
index ef5192e..30a82c6 100644
--- a/draw/scale_test.go
+++ b/draw/scale_test.go
@@ -131,6 +131,64 @@
}
}
+// translatedImage is an image m translated by t.
+type translatedImage struct {
+ m image.Image
+ t image.Point
+}
+
+func (t *translatedImage) At(x, y int) color.Color { return t.m.At(x-t.t.X, y-t.t.Y) }
+func (t *translatedImage) Bounds() image.Rectangle { return t.m.Bounds().Add(t.t) }
+func (t *translatedImage) ColorModel() color.Model { return t.m.ColorModel() }
+
+// TestSrcTranslationInvariance tests that Scale and Transform are invariant
+// under src translations. Specifically, when some source pixels are not in the
+// bottom-right quadrant of src coordinate space, we consistently round down,
+// not round towards zero.
+func TestSrcTranslationInvariance(t *testing.T) {
+ f, err := os.Open("../testdata/testpattern.png")
+ if err != nil {
+ t.Fatalf("Open: %v", err)
+ }
+ defer f.Close()
+ src, _, err := image.Decode(f)
+ if err != nil {
+ t.Fatalf("Decode: %v", err)
+ }
+ qs := []Interpolator{
+ NearestNeighbor,
+ ApproxBiLinear,
+ CatmullRom,
+ }
+ deltas := []image.Point{
+ {+0, +0},
+ {+0, +5},
+ {+0, -5},
+ {+5, +0},
+ {-5, +0},
+ {+8, +8},
+ {+8, -8},
+ {-8, +8},
+ {-8, -8},
+ }
+
+ for _, q := range qs {
+ want := image.NewRGBA(image.Rect(0, 0, 200, 200))
+ q.Scale(want, want.Bounds(), src, src.Bounds(), nil)
+ for _, delta := range deltas {
+ tsrc := &translatedImage{src, delta}
+
+ got := image.NewRGBA(image.Rect(0, 0, 200, 200))
+ q.Scale(got, got.Bounds(), tsrc, tsrc.Bounds(), nil)
+ if !bytes.Equal(got.Pix, want.Pix) {
+ t.Errorf("pix differ for delta=%v, q=%T", delta, q)
+ }
+
+ // TODO: Transform.
+ }
+ }
+}
+
// The fooWrapper types wrap the dst or src image to avoid triggering the
// type-specific fast path implementations.
type (
diff --git a/testdata/testpattern.png b/testdata/testpattern.png
new file mode 100644
index 0000000..ec87bb5
--- /dev/null
+++ b/testdata/testpattern.png
Binary files differ
