Thumbnail generation

kobo-uncaged/util.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"image"
 	"os"
 	"path/filepath"
 	"strings"
@@ -74,3 +75,15 @@ func readJSON(fn string, out interface{}) (emptyOrNotExist bool, err error) {
 
 	return false, json.NewDecoder(f).Decode(out)
 }
+
+// resizeKeepAspectRatioByExpanding resizes a sz to fill bounds while keeping
+// the aspect ratio. It is based on Qt::KeepAspectRatioByExpanding.
+func resizeKeepAspectRatioByExpanding(sz image.Point, bounds image.Point) image.Point {
+	if sz.X == 0 || sz.Y == 0 {
+		return sz
+	}
+	if rw := bounds.Y * sz.X / sz.Y; rw >= bounds.X {
+		return image.Pt(rw, bounds.Y)
+	}
+	return image.Pt(bounds.X, bounds.Y*sz.Y/sz.X)
+}

kobo-uncaged/util_test.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"image"
+	"testing"
+)
+
+func TestResizeKeepAspectRatioByExpanding(t *testing.T) {
+	for _, tc := range []struct{ sz, bounds, res image.Point }{
+		// don't resize if width or height is zero
+		{image.Pt(0, 0), image.Pt(0, 0), image.Pt(0, 0)},
+		{image.Pt(1, 0), image.Pt(0, 0), image.Pt(1, 0)},
+		{image.Pt(0, 1), image.Pt(0, 0), image.Pt(0, 1)},
+		// same aspect ratio
+		{image.Pt(1, 1), image.Pt(1, 1), image.Pt(1, 1)},
+		{image.Pt(1, 1), image.Pt(5, 5), image.Pt(5, 5)},
+		{image.Pt(5, 5), image.Pt(1, 1), image.Pt(1, 1)},
+		// limited by width
+		{image.Pt(2, 3), image.Pt(6, 6), image.Pt(6, 9)},
+		{image.Pt(2, 4), image.Pt(6, 6), image.Pt(6, 12)},
+		{image.Pt(6, 9), image.Pt(2, 3), image.Pt(2, 3)},
+		{image.Pt(6, 12), image.Pt(2, 4), image.Pt(2, 4)},
+		// limited by height
+		{image.Pt(3, 2), image.Pt(6, 6), image.Pt(9, 6)},
+		{image.Pt(4, 2), image.Pt(6, 6), image.Pt(12, 6)},
+		{image.Pt(9, 6), image.Pt(3, 2), image.Pt(3, 2)},
+		{image.Pt(12, 6), image.Pt(4, 2), image.Pt(4, 2)},
+	} {
+		if rz := resizeKeepAspectRatioByExpanding(tc.sz, tc.bounds); !rz.Eq(tc.res) {
+			t.Errorf("resize %s to %s: expected %s, got %s", tc.sz, tc.bounds, tc.res, rz)
+		}
+	}
+}