Replace false rounding scaler with self written one.

cmd/mtwebmapper/TODO

@@ -1,3 +1 @@
-* Use a scaler that uses the fact that tiles are powers of 
-  two and do _not_ round up/or down nearest neighbor interpolation.
 * Generate and use ETags to improve caching behavior.

cmd/mtwebmapper/main.go

@@ -8,6 +8,7 @@ import (
 	"flag"
 	"fmt"
 	"image"
+	"image/color"
 	"image/png"
 	"log"
 	"net/http"
@@ -19,9 +20,42 @@ import (
 	"bitbucket.org/s_l_teichmann/mtredisalize/common"
 
 	"github.com/gorilla/mux"
-	"github.com/nfnt/resize"
 )
 
+func blowUp(src image.Image) *image.RGBA {
+
+	// TODO: Use fix point arithmetic, fast path for image.RGBA
+
+	dst := image.NewRGBA(image.Rect(0, 0, 256, 256))
+
+	sw, sh := src.Bounds().Dx(), src.Bounds().Dy()
+
+	dx := float32(sw) / float32(256)
+	dy := float32(sh) / float32(256)
+
+	bx, by := src.Bounds().Min.X, src.Bounds().Min.Y
+
+	py := float32(by)
+	for y := 0; y < 256; y++ {
+		sy := int(py)
+		ox := -1
+		px := float32(bx)
+		var col color.Color
+		for x := 0; x < 256; x++ {
+			sx := int(px)
+			if sx != ox { // Minimize interface indirection access.
+				ox = sx
+				col = src.At(sx, sy)
+			}
+			dst.Set(x, y, col)
+			px += dx
+		}
+		py += dy
+	}
+
+	return dst
+}
+
 func toUint(s string) uint {
 	var err error
 	var x int
@@ -102,8 +136,7 @@ func main() {
 		}
 
 		img = si.SubImage(image.Rect(int(xo), int(yo), int(xo+w), int(yo+w)))
-		//fmt.Printf("%s\n", img.Bounds())
-		img = resize.Resize(256, 256, img, resize.NearestNeighbor)
+		img = blowUp(img)
 
 		var buf bytes.Buffer
 		if err := png.Encode(&buf, img); err != nil {