/// <summary>
/// Gets a tile at a higher zoom level and scales part of it for the requested tile
/// </summary>
/// <param name="topLeftTile">The top left tile coordinates</param>
/// <param name="zoomLevel">The requested zoom level</param>
/// <param name="path">The file path</param>
/// <param name="generatedName">The name of the DXF file (for design and alignment files it is generated)</param>
/// <param name="filespaceId">The filespace ID</param>
/// <param name="maxZoomLevel">The maximum zoom level for which tiles have been generated</param>
/// <param name="numTiles">The number of tiles for the requested zoom level</param>
/// <returns>A scaled tile</returns>
private async Task <byte[]> GetTileAtHigherZoom(Point topLeftTile, int zoomLevel, string path,
string generatedName, string filespaceId, int maxZoomLevel, int numTiles)
{
int zoomLevelFound = maxZoomLevel;
// Calculate the tile coords of the higher zoom level tile that covers the requested tile
Point ptRequestedTile = new Point(topLeftTile.y, topLeftTile.x);
Point ptRequestedPixel = WebMercatorProjection.TileToPixel(ptRequestedTile);
int numTilesAtRequestedZoomLevel = numTiles;
Point ptRequestedWorld =
WebMercatorProjection.PixelToWorld(ptRequestedPixel, numTilesAtRequestedZoomLevel);
int numTilesAtFoundZoomLevel = TileServiceUtils.NumberOfTiles(maxZoomLevel);
Point ptHigherPixel = WebMercatorProjection.WorldToPixel(ptRequestedWorld, numTilesAtFoundZoomLevel);
Point ptHigherTile = WebMercatorProjection.PixelToTile(ptHigherPixel);
//Note PixelToTile uses Math.Floor so this tile coordinate will be the top left of the tile
// With the new tile coords of the higher zoom level tile, see if it exists on TCC
string fullHigherTileName =
$"{FileUtils.ZoomPath(FileUtils.TilePath(path, generatedName), zoomLevelFound)}/{ptHigherTile.y}/{ptHigherTile.x}.png";
log.LogDebug("DxfTileExecutor: looking for higher tile {0}", fullHigherTileName);
byte[] tileData = await DownloadTile(filespaceId, fullHigherTileName, "higher");
if (tileData != null)
{
tileData = ScaleTile(tileData, zoomLevel - zoomLevelFound, ptHigherTile, ptRequestedWorld,
numTilesAtFoundZoomLevel);
}
return(tileData);
}
/// <summary>
/// Scales a tile
/// </summary>
/// <param name="tileData">The tile to scale</param>
/// <param name="zoomLevelDifference">The difference between the downloaded tile and the rqeuested tile zoom levels</param>
/// <param name="ptHigherTile"></param>
/// <param name="ptRequestedWorld"></param>
/// <param name="numTilesAtFoundZoomLevel">The number of tiles for the higher zoom level</param>
/// <returns>A scaled tile</returns>
private byte[] ScaleTile(byte[] tileData, int zoomLevelDifference, Point ptHigherTile, Point ptRequestedWorld,
int numTilesAtFoundZoomLevel)
{
// Calculate the tile coords of the BR corner of the higher zoom level tile
// so that we can identify which sub-part of it to crop and scale
Point ptHigherTileTopLeft = ptHigherTile;
Point ptHigherTileBotRight = new Point(ptHigherTile.y + 1, ptHigherTile.x + 1);
// Calculate the sub-tile rectangle that we need to crop out of the higher tile
// using a simple proportion calculation based on which part of the higher tile
// covers the original requested tile in world coordinates
Point ptHigherWorldTopLeft =
WebMercatorProjection.PixelToWorld(WebMercatorProjection.TileToPixel(ptHigherTileTopLeft),
numTilesAtFoundZoomLevel);
Point ptHigherWorldBotRight =
WebMercatorProjection.PixelToWorld(WebMercatorProjection.TileToPixel(ptHigherTileBotRight),
numTilesAtFoundZoomLevel);
double ratioX = (ptRequestedWorld.x - ptHigherWorldTopLeft.x) /
(ptHigherWorldBotRight.x - ptHigherWorldTopLeft.x);
double ratioY = (ptRequestedWorld.y - ptHigherWorldTopLeft.y) /
(ptHigherWorldBotRight.y - ptHigherWorldTopLeft.y);
int startX = (int)Math.Floor(WebMercatorProjection.TILE_SIZE * ratioX);
int startY = (int)Math.Floor(WebMercatorProjection.TILE_SIZE * ratioY);
// Calculate how much up-scaling of higher level zoom tile we need to do
// based on the difference between the requested and higher zoom levels
int croppedTileSize = WebMercatorProjection.TILE_SIZE / (1 << zoomLevelDifference);
// Set the crop rectangle and draw it into a new bitmap, scaling it up to the standard tile size
Rectangle cropRect = new Rectangle(startX, startY, croppedTileSize, croppedTileSize);
log.LogDebug("DxfTileExecutor: crop rectangle x = {0}, y = {1}, size = {2}", startX, startY,
croppedTileSize);
//source bitmap
using (var tileStream = new MemoryStream(tileData))
using (Bitmap higherBitmap = new Bitmap(tileStream))
//destination bitmap
using (Bitmap target = new Bitmap(WebMercatorProjection.TILE_SIZE, WebMercatorProjection.TILE_SIZE))
using (Graphics g = Graphics.FromImage(target))
{
g.CompositingMode = CompositingMode.SourceCopy;
g.CompositingQuality = CompositingQuality.HighQuality;
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.SmoothingMode = SmoothingMode.HighQuality;
g.PixelOffsetMode = PixelOffsetMode.HighQuality;
g.DrawImage(higherBitmap, new Rectangle(0, 0, target.Width, target.Height), cropRect,
GraphicsUnit.Pixel);
g.Flush();
return(target.BitmapToByteArray());
}
}
