Data commit

Task/Bitmap-Read-a-PPM-file/Go/bitmap-read-a-ppm-file-1.go

@@ -0,0 +1,68 @@
+package raster
+
+import (
+    "errors"
+    "io"
+    "io/ioutil"
+    "os"
+    "regexp"
+    "strconv"
+)
+
+// ReadFrom constructs a Bitmap object from an io.Reader.
+func ReadPpmFrom(r io.Reader) (b *Bitmap, err error) {
+    var all []byte
+    all, err = ioutil.ReadAll(r)
+    if err != nil {
+        return
+    }
+    bss := rxHeader.FindSubmatch(all)
+    if bss == nil {
+        return nil, errors.New("unrecognized ppm header")
+    }
+    x, _ := strconv.Atoi(string(bss[3]))
+    y, _ := strconv.Atoi(string(bss[6]))
+    maxval, _ := strconv.Atoi(string(bss[9]))
+    if maxval > 255 {
+        return nil, errors.New("16 bit ppm not supported")
+    }
+    allCmts := append(append(append(bss[1], bss[4]...), bss[7]...), bss[10]...)
+    b = NewBitmap(x, y)
+    b.Comments = rxComment.FindAllString(string(allCmts), -1)
+    b3 := all[len(bss[0]):]
+    var n1 int
+    for i := range b.px {
+        b.px[i].R = byte(int(b3[n1]) * 255 / maxval)
+        b.px[i].G = byte(int(b3[n1+1]) * 255 / maxval)
+        b.px[i].B = byte(int(b3[n1+2]) * 255 / maxval)
+        n1 += 3
+    }
+    return
+}
+
+const (
+    // single whitespace character
+    ws = "[ \n\r\t\v\f]"
+    // isolated comment
+    cmt = "#[^\n\r]*"
+    // comment sub expression
+    cmts = "(" + ws + "*" + cmt + "[\n\r])"
+    // number with leading comments
+    num = "(" + cmts + "+" + ws + "*|" + ws + "+)([0-9]+)"
+)
+
+var rxHeader = regexp.MustCompile("^P6" + num + num + num +
+    "(" + cmts + "*" + ")" + ws)
+var rxComment = regexp.MustCompile(cmt)
+
+// ReadFile writes binary P6 format PPM from the specified filename.
+func ReadPpmFile(fn string) (b *Bitmap, err error) {
+    var f *os.File
+    if f, err = os.Open(fn); err != nil {
+        return
+    }
+    if b, err = ReadPpmFrom(f); err != nil {
+        return
+    }
+    return b, f.Close()
+}

Task/Bitmap-Read-a-PPM-file/Go/bitmap-read-a-ppm-file-2.go

@@ -0,0 +1,28 @@
+package main
+
+// Files required to build supporting package raster are found in:
+// * This task (immediately above)
+// * Bitmap
+// * Grayscale image
+// * Write a PPM file
+
+import (
+    "raster"
+    "fmt"
+)
+
+func main() {
+    // (A file with this name is output by the Go solution to the task
+    // "Bitmap/Read an image through a pipe," but of course any 8-bit
+    //  P6 PPM file should work.)
+    b, err := raster.ReadPpmFile("pipein.ppm")
+    if err != nil {
+        fmt.Println(err)
+        return
+    }
+    b = b.Grmap().Bitmap()
+    err = b.WritePpmFile("grayscale.ppm")
+    if err != nil {
+        fmt.Println(err)
+    }
+}