Add http server

epd/epd.go

@@ -0,0 +1,70 @@
+package epd
+
+import (
+	"image"
+	"image/color"
+	_ "image/gif"
+	_ "image/jpeg"
+	_ "image/png"
+	"io"
+
+	"golang.org/x/image/draw"
+)
+
+// Returns a new Rectangle that is resized and centered in `dst`
+func fitRectInto(src *image.Rectangle, dst *image.Rectangle) image.Rectangle {
+	var targetWidth int
+	var targetHeight int
+	var scale float64
+
+	srcRatio := float64(src.Max.X) / float64(src.Max.Y)
+	dstRatio := float64(dst.Max.X) / float64(dst.Max.Y)
+
+	if srcRatio < dstRatio {
+		// center horizontally, scale vertically
+		scale = float64(dst.Max.Y) / float64(src.Max.Y)
+	} else {
+		// center vertically, scale horizontally
+		scale = float64(dst.Max.X) / float64(src.Max.X)
+	}
+
+	targetWidth = int(float64(src.Max.X) * scale)
+	targetHeight = int(float64(src.Max.Y) * scale)
+
+	targetX := (dst.Max.X - targetWidth) / 2
+	targetY := (dst.Max.Y - targetHeight) / 2
+
+	return image.Rect(targetX, targetY, targetWidth+targetX, targetHeight+targetY)
+}
+
+// Converts a GIF, JPEG or PNG into a 16-color grayscale image. A single pixel
+// is represented by 4 bits and each byte holds two pixels. The final 4-bits of
+// the last byte may be discarded if width * height is odd.
+func ConvertImage(input io.Reader, width int, height int) ([]byte, error) {
+	src, _, err := image.Decode(input)
+	if err != nil {
+		return nil, err
+	}
+	dst := image.NewGray(image.Rect(0, 0, width, height))
+
+	srcBounds := src.Bounds()
+	targetRect := fitRectInto(&srcBounds, &dst.Rect)
+
+	draw.Draw(dst, dst.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)
+	draw.CatmullRom.Scale(dst, targetRect, src, src.Bounds(), draw.Over, nil)
+
+	// the actual conversion works by packing two nibbles together in a byte
+	var result = make([]byte, (width*height+1)/2)
+	for i, p := range dst.Pix {
+		res := uint8((uint16(p) + 8) / 16)
+		if i%2 == 0 {
+			result[i/2] = (res << 4)
+		} else {
+			// note that integer division makes sure we're writing at the same
+			// index for odd and even indices
+			result[i/2] |= res
+		}
+	}
+
+	return result, nil
+}