// checkDone tests whether we have generated all the tiles.
// If so, it creates a zip task on the zipper backend.
func checkDone(c appengine.Context, oKey *datastore.Key) (done bool, err error) {
// Create a zip task if we're done and one hasn't been created already.
tx := func(c appengine.Context) error {
o := new(Overlay)
err := datastore.Get(c, oKey, o)
if err != nil {
return err
}
// Check whether we have generated all the tiles.
count, err := datastore.NewQuery("Tile").Ancestor(oKey).Count(c)
if err != nil {
return err
}
done = o.Tiles >= count
if !done || o.Zip != "" {
return nil
}
// Create a task to build the zip file,
// targeting the zipper backend.
task := taskqueue.NewPOSTTask("/zip", url.Values{
"key": {oKey.Encode()},
})
if !appengine.IsDevAppServer() {
host := appengine.BackendHostname(c, zipBackend, -1)
task.Header.Set("Host", host)
}
if _, err := taskqueue.Add(c, task, zipQueue); err != nil {
return err
}
// Store a sentinel value in Zip field to prevent a
// second zip task from being created.
// This value will be overwritten by the zip task.
o.Zip = zipSentinel
_, err = datastore.Put(c, oKey, o)
return err
}
if err := datastore.RunInTransaction(c, tx, nil); err != nil {
return false, err
}
return done, nil
}
// processHandler initiates the processing of an Overlay, including kicking off
// appropriate slice tasks.
func processHandler(c appengine.Context, w http.ResponseWriter, r *http.Request) *appError {
if r.Method != "POST" {
return &appError{nil, "must use POST", http.StatusMethodNotAllowed}
}
// Get the Overlay from the datastore.
k, o, err := getOverlay(r)
if err != nil {
return appErrorf(err, "overlay not found")
}
// Process the request.
if o.TopLeft, err = parsePair(r.FormValue("topLeft")); err != nil {
return appErrorf(err, "invalid parameter topLeft")
}
if o.TopRight, err = parsePair(r.FormValue("topRight")); err != nil {
return appErrorf(err, "invalid parameter topLeft")
}
if o.BottomRight, err = parsePair(r.FormValue("bottomRight")); err != nil {
return appErrorf(err, "invalid parameter bottomRight")
}
// Compute the transformation matrix.
a := graphics.I.Scale(1/float64(o.Width), 1/float64(o.Height)).
Mul(inverse(graphics.Affine{
o.TopRight[0] - o.TopLeft[0], o.BottomRight[0] - o.TopRight[0], o.TopLeft[0],
o.TopRight[1] - o.TopLeft[1], o.BottomRight[1] - o.TopRight[1], o.TopLeft[1],
0, 0, 1,
}))
o.Transform = []float64(a[:])
// TODO(cbro): get min/max zoom from user.
o.MinZoom = 0
o.MaxZoom = 21
// Compute tiles to be generated.
var tiles []*Tile
for zoom := o.MinZoom; zoom <= o.MaxZoom; zoom++ {
tiles = append(tiles, tilesForZoom(o, zoom)...)
}
o.Tiles = len(tiles)
// Create a channel between the app and the client's browser.
token, err := channel.Create(c, k.Encode())
if err != nil {
return appErrorf(err, "couldn't create browser channel")
}
// Put the updated Overlay into the datastore.
if _, err := datastore.Put(c, k, o); err != nil {
return appErrorf(err, "could not save overlay to datastore")
}
// Create tasks to generate tiles.
tasks := tileTasks(k.Encode(), tiles)
if err := addTasks(c, tasks, tileQueue); err != nil {
return appErrorf(err, "could not start tiling process")
}
// Create task to start slice process.
task := taskqueue.NewPOSTTask("/slice", url.Values{"key": {k.Encode()}})
for i := 0; i < sliceBackends; i++ {
host := appengine.BackendHostname(c, sliceBackend, i)
task.Header.Set("Host", host)
if _, err := taskqueue.Add(c, task, sliceQueue); err != nil {
return appErrorf(err, "could not start tiling process")
}
}
// Send channel token as response.
w.Header().Set("Content-Type", "text/plain")
w.Write([]byte(token))
return nil
}
func backend(c appengine.Context) string {
// Use the load-balanced hostname for the "datagrabber" backend.
return "http://" + appengine.BackendHostname(c, "datagrabber", -1)
}