scaler: support FitInside, Bilinear{Fast/Accurate} variants, BiCubic

DirectThumbnailer.go

@@ -50,7 +50,10 @@ func (this *DirectThumbnailer) RenderFile(absPath string) ([]byte, error) {
 
 	// Scale
 
-	dest := this.scaleImage(src)
+	dest, err := this.scaleImage(src)
+	if err != nil {
+		return nil, err
+	}
 
 	// Rasterise result
 

config.go

@@ -14,7 +14,9 @@ const (
 	FitInside  AspectFormat = 82 // Crop to dimensions
 
 	NearestNeighbour ScaleFormat = 120
-	Bilinear         ScaleFormat = 121
+	BilinearFast     ScaleFormat = 121
+	BilinearAccurate ScaleFormat = 122
+	Bicubic          ScaleFormat = 123
 )
 
 type Config struct {

scaler.go

@@ -7,13 +7,18 @@ import (
 	"image/png"
 
 	"golang.org/x/image/bmp"
+	"golang.org/x/image/draw"
 )
 
-func (this *DirectThumbnailer) scaleImage(src image.Image) image.Image {
+func (this *DirectThumbnailer) scaleImage(src image.Image) (image.Image, error) {
 	srcW := src.Bounds().Max.X
 	srcH := src.Bounds().Max.Y
-	destW := 0
-	destH := 0
+	var srcCopyPosition, destCopyPosition image.Rectangle
+
+	switch this.cfg.Aspect {
+	case FitInside:
+
+		var destW, destH int
 
 		if srcW > srcH {
 			destW = this.cfg.Width
@@ -26,40 +31,52 @@ func (this *DirectThumbnailer) scaleImage(src image.Image) image.Image {
 		offsetX := (this.cfg.Width - destW) / 2
 		offsetY := (this.cfg.Height - destH) / 2
 
-	scaleW := float64(srcW) / float64(destW)
-	scaleH := float64(srcH) / float64(destH)
+		srcCopyPosition = src.Bounds()
+		destCopyPosition = image.Rect(offsetX, offsetY, destW+offsetX, destH+offsetY)
 
-	dest := image.NewRGBA(image.Rectangle{Max: image.Point{X: this.cfg.Width, Y: this.cfg.Height}})
+	case FitOutside:
+
+		var srcSmallestDim, offsetX, offsetY int
+		if srcW > srcH {
+			// Landscape
+			srcSmallestDim = srcH
+			offsetY = 0
+			offsetX = (srcW - srcH) / 2
+		} else {
+			// Portrait (or square)
+			srcSmallestDim = srcW
+			offsetY = (srcH - srcW) / 2
+			offsetX = 0
+		}
+
+		srcCopyPosition = image.Rect(offsetX, offsetY, srcSmallestDim+offsetX, srcSmallestDim+offsetY)
+		destCopyPosition = image.Rect(0, 0, this.cfg.Width, this.cfg.Height)
+
+	default:
+		return nil, ErrInvalidOption
+	}
+
+	//
+
+	dest := image.NewRGBA(image.Rect(0, 0, this.cfg.Width, this.cfg.Height))
+
+	// For a transparent destination, Op.Src is faster than Op.Over
 
 	switch this.cfg.Scale {
-
-	case Bilinear:
-
-		for y := 0; y < destH; y += 1 {
-			for x := 0; x < destW; x += 1 {
-				c00 := src.At(int(float64(x)*scaleW), int(float64(y)*scaleH))
-				c01 := src.At(int((float64(x)+0.5)*scaleW), int(float64(y)*scaleH))
-				c10 := src.At(int(float64(x)*scaleW), int((float64(y)+0.5)*scaleH))
-				c11 := src.At(int((float64(x)+0.5)*scaleW), int((float64(y)+0.5)*scaleH))
-				cBlend := Blend(Blend(c00, c01), Blend(c10, c11))
-				dest.Set(x+offsetX, y+offsetY, cBlend)
-
-			}
-		}
-
 	case NearestNeighbour:
+		draw.NearestNeighbor.Scale(dest, destCopyPosition, src, srcCopyPosition, draw.Src, nil)
 
-		for y := 0; y < destH; y += 1 {
-			for x := 0; x < destW; x += 1 {
-				mapx := int(float64(x) * scaleW)
-				mapy := int(float64(y) * scaleH)
-				dest.Set(x+offsetX, y+offsetY, src.At(mapx, mapy))
-			}
+	case BilinearFast:
+		draw.ApproxBiLinear.Scale(dest, destCopyPosition, src, srcCopyPosition, draw.Src, nil)
+
+	case BilinearAccurate:
+		draw.BiLinear.Scale(dest, destCopyPosition, src, srcCopyPosition, draw.Src, nil)
+
+	case Bicubic:
+		draw.CatmullRom.Scale(dest, destCopyPosition, src, srcCopyPosition, draw.Src, nil)
 	}
 
-	}
-
-	return dest
+	return dest, nil
 }
 
 func (this *DirectThumbnailer) encode(dest image.Image) ([]byte, error) {