func (surfacer *TileOverlaySurface) downloadTiles() error {
// for the tiles, 0,0 is northwest. For the surface, 0,0 is south west
verticalFlipOffset := uint64(surfacer.Surface.Height - 1)
var fetchErr error
var wait sync.WaitGroup
numTiles := (surfacer.xTileMax - surfacer.xTileMax + 1) * (surfacer.yTileMax - surfacer.yTileMin + 1)
tiles := make(chan [2]uint64, numTiles)
wait.Add(surfacer.DownloadGoroutines)
for thread := 0; thread < surfacer.DownloadGoroutines; thread++ {
go func() {
defer wait.Done()
for t := range tiles {
x, y := t[0], t[1]
if fetchErr != nil {
return
}
// fetch tile data
url := utils.BuildTileURL(surfacer.SourceURLTemplate, x, y, surfacer.level)
body, err := utils.FetchURL(url, surfacer.DownloadRetries)
if err == nil {
var k, l uint64
img, _, err := image.Decode(body)
body.Close()
if err != nil {
fetchErr = err
return
}
xStart := (x - surfacer.xTileMin) * 256
yStart := (y - surfacer.yTileMin) * 256
for k = 0; k < 256; k++ {
offset := verticalFlipOffset - (yStart + k)
for l = 0; l < 256; l++ {
// while this does a matrix transpose, I did not get any speedup when trying to mess with this.
surfacer.Surface.Grid[xStart+l][offset] = surfacer.ColorValueFunc(img.At(int(l), int(k)), surfacer.targetColor)
}
}
} else {
fetchErr = err
return
}
}
}()
}
for i := surfacer.xTileMin; i <= surfacer.xTileMax; i++ {
for j := surfacer.yTileMin; j <= surfacer.yTileMax; j++ {
tiles <- [2]uint64{i, j}
}
}
close(tiles)
wait.Wait()
if fetchErr != nil {
return fetchErr
}
return nil
}
// downloadTiles downloads the strava heat data and puts it in the correct locations in the surface.
// It starts up surfacer.DownloadGoroutines goroutines to download the data in parallel.
func (surfacer *StravaHeatSurface) downloadTiles() error {
// for the tiles, 0,0 is northwest. For the surface, 0,0 is south west
verticalFlipOffset := uint64(surfacer.surface.Height - 1)
var fetchErr error
var wait sync.WaitGroup
numTiles := (surfacer.xTileMax - surfacer.xTileMax + 1) * (surfacer.yTileMax - surfacer.yTileMin + 1)
tiles := make(chan [2]uint64, numTiles)
wait.Add(surfacer.DownloadGoroutines)
for thread := 0; thread < surfacer.DownloadGoroutines; thread++ {
go func() {
defer wait.Done()
for t := range tiles {
x, y := t[0], t[1]
if fetchErr != nil {
return
}
url := utils.BuildTileURL(surfacer.SourceURLTemplate, x, y, surfacer.level)
body, err := utils.FetchURL(url, surfacer.DownloadRetries)
if err == nil {
var k, l uint64
data := &tileData{}
err = json.NewDecoder(body).Decode(&data)
body.Close()
if err != nil {
fetchErr = err
return
}
xStart := (x - surfacer.xTileMin) * 256
yStart := (y - surfacer.yTileMin) * 256
for k = 0; k < 256; k++ {
offset := verticalFlipOffset - (yStart + k)
for l = 0; l < 256; l++ {
// while this does a matrix transpose. I did not get any speedup when
// trying to mess with this.
surfacer.surface.Grid[xStart+l][offset] = data.Data[k*256+l]
}
}
} else {
fetchErr = err
return
}
}
}()
}
for i := surfacer.xTileMin; i <= surfacer.xTileMax; i++ {
for j := surfacer.yTileMin; j <= surfacer.yTileMax; j++ {
tiles <- [2]uint64{i, j}
}
}
close(tiles)
wait.Wait()
if fetchErr != nil {
return fetchErr
}
return nil
}