LazMapViewer: Implement zoomed preview tiles. Patch by Ekkehard Domning. Adapt drawing engines and full demo projects.

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@8835 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/lazmapviewer/examples/fulldemo/MapViewer_Demo.lpr

@@ -5,8 +5,8 @@ program MapViewer_Demo;
 uses
   {$IFDEF UNIX}cthreads,{$ENDIF}
   Interfaces, // this includes the LCL widgetset
-  Forms, printer4lazarus, Main, gpslistform, globals, gpsptform
+  Forms,
-  { you can add units after this };
+  Main, gpslistform;
 
 {$R *.res}
 

components/lazmapviewer/examples/fulldemo/main.lfm

@@ -855,13 +855,13 @@ object MainForm: TMainForm
         State = cbChecked
         TabOrder = 8
       end
-      object ColorButton1: TColorButton
+      object clbBackColor: TColorButton
         AnchorSideLeft.Control = cbCyclicView
-        AnchorSideTop.Control = CbUseThreads
+        AnchorSideTop.Control = CbDoubleBuffer
         AnchorSideTop.Side = asrCenter
         Left = 130
         Height = 25
-        Top = 78
+        Top = 103
         Width = 105
         BorderWidth = 2
         ButtonColorAutoSize = False
@@ -869,7 +869,20 @@ object MainForm: TMainForm
         ButtonColor = clWhite
         Caption = 'Map backgr.'
         Margin = 4
-        OnColorChanged = ColorButton1ColorChanged
+        OnColorChanged = clbBackColorColorChanged
+      end
+      object CbPreviewTiles: TCheckBox
+        AnchorSideLeft.Control = cbCyclicView
+        AnchorSideTop.Control = CbUseThreads
+        Left = 130
+        Height = 19
+        Top = 81
+        Width = 83
+        Caption = 'Preview tiles'
+        Checked = True
+        OnChange = CbPreviewTilesChange
+        State = cbChecked
+        TabOrder = 9
       end
     end
   end

components/lazmapviewer/examples/fulldemo/main.pas

@@ -33,7 +33,8 @@ type
     cbPOITextBgColor: TColorBox;
     CbZoomToCursor: TCheckBox;
     cbCyclicView: TCheckBox;
-    ColorButton1: TColorButton;
+    CbPreviewTiles: TCheckBox;
+    clbBackColor: TColorButton;
     FontDialog: TFontDialog;
     GbCenterCoords: TGroupBox;
     GbScreenSize: TGroupBox;
@@ -82,12 +83,13 @@ type
     procedure CbFoundLocationsDrawItem(Control: TWinControl; Index: Integer;
       ARect: TRect; State: TOwnerDrawState);
     procedure cbPOITextBgColorChange(Sender: TObject);
+    procedure CbPreviewTilesChange(Sender: TObject);
     procedure CbProvidersChange(Sender: TObject);
     procedure CbShowPOIImageChange(Sender: TObject);
     procedure CbUseThreadsChange(Sender: TObject);
     procedure CbDistanceUnitsChange(Sender: TObject);
     procedure CbZoomToCursorChange(Sender: TObject);
-    procedure ColorButton1ColorChanged(Sender: TObject);
+    procedure clbBackColorColorChanged(Sender: TObject);
     procedure FormCreate(Sender: TObject);
     procedure FormDestroy(Sender: TObject);
     procedure FormShow(Sender: TObject);
@@ -381,6 +383,11 @@ begin
   MapView.POITextBgColor := cbPOITextBgColor.Selected;
 end;
 
+procedure TMainForm.CbPreviewTilesChange(Sender: TObject);
+begin
+  MapView.DrawPreviewTiles := CbPreviewTiles.Checked;
+end;
+
 procedure TMainForm.CbProvidersChange(Sender: TObject);
 begin
   MapView.MapProvider := CbProviders.Text;
@@ -412,9 +419,9 @@ begin
   MapView.ZoomToCursor := CbZoomToCursor.Checked;
 end;
 
-procedure TMainForm.ColorButton1ColorChanged(Sender: TObject);
+procedure TMainForm.clbBackColorColorChanged(Sender: TObject);
 begin
-  MapView.InactiveColor := ColorButton1.ButtonColor;
+  MapView.InactiveColor := clbBackColor.ButtonColor;
 end;
 
 procedure TMainForm.ClearFoundLocations;
@@ -462,6 +469,7 @@ begin
   CbUseThreads.Checked := MapView.UseThreads;
   CbDoubleBuffer.Checked := MapView.DoubleBuffered;
   CbPOITextBgColor.Selected := MapView.POITextBgColor;
+  ClbBackColor.ButtonColor := MapView.InactiveColor;
 
   InfoPositionLongitude.Caption := '';
   InfoPositionLatitude.Caption := '';
@@ -740,6 +748,7 @@ begin
     pt.Lat := StrToFloatDef(ini.ReadString('MapView', 'Center.Latitude', ''), 0.0, PointFormatSettings);
     MapView.Center := pt;
     MapView.InactiveColor := ini.ReadInteger('MapView', 'MapBkgrColor', MapView.InactiveColor);
+    clbBackColor.ButtonColor := MapView.InactiveColor;
 
     s := ini.ReadString('MapView', 'DistanceUnits', '');
     if s <> '' then begin

components/lazmapviewer/examples/fulldemo_with_addons/main.lfm

@@ -37,9 +37,9 @@ object MainForm: TMainForm
     Height = 640
     Top = 0
     Width = 275
-    ActivePage = PgData
+    ActivePage = PgConfig
     Align = alRight
-    TabIndex = 0
+    TabIndex = 1
     TabOrder = 1
     object PgData: TTabSheet
       Caption = 'Data'
@@ -875,6 +875,36 @@ object MainForm: TMainForm
         State = cbChecked
         TabOrder = 10
       end
+      object CbPreviewTiles: TCheckBox
+        AnchorSideLeft.Control = CbCyclic
+        AnchorSideTop.Control = CbUseThreads
+        AnchorSideTop.Side = asrCenter
+        Left = 130
+        Height = 19
+        Top = 175
+        Width = 83
+        Caption = 'Preview tiles'
+        Checked = True
+        OnChange = CbPreviewTilesChange
+        State = cbChecked
+        TabOrder = 11
+      end
+      object clbBackColor: TColorButton
+        AnchorSideLeft.Control = CbPreviewTiles
+        AnchorSideTop.Control = CbDoubleBuffer
+        AnchorSideTop.Side = asrCenter
+        Left = 130
+        Height = 25
+        Top = 197
+        Width = 105
+        BorderWidth = 2
+        ButtonColorAutoSize = False
+        ButtonColorSize = 15
+        ButtonColor = clWhite
+        Caption = 'Map backgr.'
+        Margin = 4
+        OnColorChanged = clbBackColorColorChanged
+      end
     end
   end
   object GeoNames: TMVGeoNames

components/lazmapviewer/examples/fulldemo_with_addons/main.pas

@@ -36,6 +36,8 @@ type
     cbPOITextBgColor: TColorBox;
     CbZoomToCursor: TCheckBox;
     CbCyclic: TCheckBox;
+    CbPreviewTiles: TCheckBox;
+    clbBackColor: TColorButton;
     FontDialog: TFontDialog;
     GbCenterCoords: TGroupBox;
     GbScreenSize: TGroupBox;
@@ -83,12 +85,14 @@ type
     procedure CbFoundLocationsDrawItem(Control: TWinControl; Index: Integer;
       ARect: TRect; State: TOwnerDrawState);
     procedure cbPOITextBgColorChange(Sender: TObject);
+    procedure CbPreviewTilesChange(Sender: TObject);
     procedure CbProvidersChange(Sender: TObject);
     procedure CbShowPOIImageChange(Sender: TObject);
     procedure CbUseThreadsChange(Sender: TObject);
     procedure CbDistanceUnitsChange(Sender: TObject);
     procedure CbZoomToCursorChange(Sender: TObject);
     procedure CbCyclicChange(Sender: TObject);
+    procedure clbBackColorColorChanged(Sender: TObject);
     procedure FormCreate(Sender: TObject);
     procedure FormDestroy(Sender: TObject);
     procedure FormShow(Sender: TObject);
@@ -346,6 +350,11 @@ begin
   MapView.POITextBgColor := cbPOITextBgColor.Selected;
 end;
 
+procedure TMainForm.CbPreviewTilesChange(Sender: TObject);
+begin
+  MapView.DrawPreviewTiles := CbPreviewTiles.Checked;
+end;
+
 procedure TMainForm.CbProvidersChange(Sender: TObject);
 begin
   MapView.MapProvider := CbProviders.Text;
@@ -380,6 +389,11 @@ begin
   MapView.Cyclic := CbCyclic.Checked;
 end;
 
+procedure TMainForm.clbBackColorColorChanged(Sender: TObject);
+begin
+  MapView.InactiveColor := clbBackColor.ButtonColor;
+end;
+
 procedure TMainForm.ClearFoundLocations;
 var
   i: Integer;
@@ -420,6 +434,7 @@ begin
   CbUseThreads.Checked := MapView.UseThreads;
   CbDoubleBuffer.Checked := MapView.DoubleBuffered;
   CbPOITextBgColor.Selected := MapView.POITextBgColor;
+  clbBackColor.ButtonColor := MapView.InactiveColor;
 
   InfoPositionLongitude.Caption := '';
   InfoPositionLatitude.Caption := '';
@@ -610,6 +625,8 @@ begin
     pt.Lon := StrToFloatDef(ini.ReadString('MapView', 'Center.Longitude', ''), 0.0, PointFormatSettings);
     pt.Lat := StrToFloatDef(ini.ReadString('MapView', 'Center.Latitude', ''), 0.0, PointFormatSettings);
     MapView.Center := pt;
+    MapView.InactiveColor := ini.ReadInteger('MapView', 'MapBkgrColor', MapView.InactiveColor);
+    clbBackColor.ButtonColor := MapView.InactiveColor;
 
     s := ini.ReadString('MapView', 'DistanceUnits', '');
     if s <> '' then begin
@@ -737,6 +754,7 @@ begin
     ini.WriteInteger('MapView', 'Zoom', MapView.Zoom);
     ini.WriteString('MapView', 'Center.Longitude', FloatToStr(MapView.Center.Lon, PointFormatSettings));
     ini.WriteString('MapView', 'Center.Latitude', FloatToStr(MapView.Center.Lat, PointFormatSettings));
+    ini.WriteInteger('MapView', 'MapBkgrColor', MapView.InactiveColor);
 
     ini.WriteString('MapView', 'DistanceUnits', DistanceUnit_Names[DistanceUnit]);
 

components/lazmapviewer/source/addons/bgra_drawingengine/mvde_bgra.pas

@@ -57,6 +57,7 @@ type
     procedure DrawBitmap(X, Y: Integer; ABitmap: TCustomBitmap;
       UseAlphaChannel: Boolean); override;
     procedure DrawLazIntfImage(X, Y: Integer; AImg: TLazIntfImage); override;
+    procedure DrawScaledLazIntfImage(DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage); override;
     procedure Ellipse(X1, Y1, X2, Y2: Integer); override;
     procedure FillPixels(X1, Y1, X2, Y2: Integer; AColor: TColor); override;
     procedure FillRect(X1, Y1, X2, Y2: Integer); override;
@@ -138,6 +139,29 @@ begin
   end;
 end;
 
+procedure TMvBGRADrawingEngine.DrawScaledLazIntfImage(
+  DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage);
+var
+  srcBmp: TBGRABitmap;
+  x, y, w, h: Integer;
+  c: TFPColor;
+begin
+  w := SrcRect.Right - SrcRect.Left;
+  h := SrcRect.Bottom - SrcRect.Top;
+  srcBmp := TBGRABitmap.Create(w, h, clWhite);
+  try
+    for y := 0 to h-1 do
+      for x := 0 to w-1 do
+      begin
+        c := ASrcImg.Colors[SrcRect.Left + x, SrcRect.Top + y];
+        srcBmp.DrawPixel(x, y, FPColorToTColor(c));
+      end;
+    FBuffer.CanvasBGRA.StretchDraw(DestRect, srcBmp);
+  finally
+    srcBmp.Free;
+  end;
+end;
+
 procedure TMvBGRADrawingEngine.Ellipse(X1, Y1, X2, Y2: Integer);
 begin
   FBuffer.CanvasBGRA.Ellipse(X1, Y1, X2, Y2);

components/lazmapviewer/source/addons/rgbgraphics_drawingengine/mvde_rgbgraphics.pas

@@ -19,7 +19,7 @@ interface
 uses
   Classes, SysUtils, Types, Graphics, IntfGraphics,
   mvDrawingEngine,
-  rgbGraphics;
+  rgbGraphics, rgbTypes;
 
 type
 
@@ -57,6 +57,7 @@ type
     procedure DrawBitmap(X, Y: Integer; ABitmap: TCustomBitmap;
       UseAlphaChannel: Boolean); override;
     procedure DrawLazIntfImage(X, Y: Integer; AImg: TLazIntfImage); override;
+    procedure DrawScaledLazIntfImage(DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage); override;
     procedure Ellipse(X1, Y1, X2, Y2: Integer); override;
     procedure FillPixels(X1, Y1, X2, Y2: Integer; AColor: TColor); override;
     procedure FillRect(X1, Y1, X2, Y2: Integer); override;
@@ -135,9 +136,10 @@ begin
   {$IFDEF DARWIN}
   rawImg.Description.Init_BPP32_A8R8G8B8_BIO_TTB(FBuffer.Width, FBuffer.Height);
   {$ELSE}
-  rawImg.Description.Init_BPP32_B8G8R8_BIO_TTB(FBuffer.Width, FBuffer.Height);
+//  rawImg.Description.Init_BPP32_B8G8R8_BIO_TTB(FBuffer.Width, FBuffer.Height);        // wp: why twice: here ...
+ // {$ENDIF}
+  rawImg.Description.Init_BPP32_B8G8R8A8_BIO_TTB(FBuffer.Width, FBuffer.Height);      // ... and here again ???
   {$ENDIF}
-  rawImg.Description.Init_BPP32_B8G8R8A8_BIO_TTB(FBuffer.Width, FBuffer.Height);
   rawImg.Data := FBuffer.Pixels;
   intfImg := TLazIntfImage.Create(rawImg, false);
   try
@@ -148,6 +150,30 @@ begin
   end;
 end;
 
+procedure TMvRGBGraphicsDrawingEngine.DrawScaledLazIntfImage(
+  DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage);
+var
+  srcBmp: TRGB32Bitmap;
+  x, y, w, h: Integer;
+  c: TFPColor;
+begin
+  w := SrcRect.Right - SrcRect.Left;
+  h := SrcRect.Bottom - SrcRect.Top;
+  srcBmp := TRGB32Bitmap.Create(w, h);
+  try
+    for y := 0 to h-1 do
+      for x := 0 to w-1 do
+      begin
+        c := ASrcImg.Colors[SrcRect.Left + x, SrcRect.Top + y];
+        srcBmp.Set32Pixel(x, y, ColorToRGB32Pixel(FPColorToTColor(c)));
+      end;
+    srcBmp.StretchTrunc(DestRect.Right - DestRect.Left, DestRect.Bottom - DestRect.Top);
+    FBuffer.Draw(DestRect.Left, DestRect.Top, srcBmp);
+  finally
+    srcBmp.Free;
+  end;
+end;
+
 procedure TMvRGBGraphicsDrawingEngine.Ellipse(X1, Y1, X2, Y2: Integer);
 begin
   FBuffer.Canvas.Ellipse(X1, Y1, X2, Y2);

components/lazmapviewer/source/mvcache.pas

@@ -48,6 +48,7 @@ Type
      destructor Destroy; override;
      Procedure Add(MapProvider: TMapProvider; const TileId: TTileId; Stream: TMemoryStream);
      Procedure GetFromCache(MapProvider: TMapProvider; const TileId: TTileId; out img: TLazIntfImage);
+     function GetPreviewFromCache(MapProvider: TMapProvider; var TileId: TTileId; out ARect: TRect): boolean;
      function InCache(MapProvider: TMapProvider; const TileId: TTileId): Boolean;
 
      property UseDisk: Boolean read FUseDisk write FUseDisk;
@@ -347,6 +348,64 @@ begin
   end;
 end;
 
+{ When TileId is not yet in the cache, the function decreases zoom level and
+  returns the TileID of a tile which already is in the cache, and in ARect
+  the rectangle coordinates to get an upscaled preview of the originally
+  requested tile. The function returns true in this case.
+  If the requested tile already is in the cache, or no containing tile is found
+  the function returns false indicating that not preview image must be
+  generated. }
+function TPictureCache.GetPreviewFromCache(MapProvider: TMapProvider;
+  var TileId: TTileId; out ARect: TRect): boolean;
+var
+  ltid: TTileId;
+  xfrac, yfrac: Double;
+  lDeltaZoom: Integer;
+  w, px, py: Integer;
+begin
+  Result := false;
+  ARect := Rect(0, 0, 0, 0);
+
+  if (TileId.Z < 0) or
+     (TileId.X < 0) or
+     (TileId.Y < 0) then exit;
+
+  if InCache(MapProvider, TileID) then
+    exit;
+
+  if TileId.Z <= 0 then
+    exit; // The whole earth as a preview, is simply the earth
+
+  // The "preview" is the part of the containing tile that covers the location of the wanted tile
+  // Every decrement of Zoom reduces the tile area by 4 (half of x and y direction)
+  // So incrementing Z and dividing X and Y in the Id will lead us to the containing tile
+  // The fraction of the division points to the location of the preview
+  // e.g 0.5 = right or lower half of the tile, when divided by 2
+  ltid := TileId;
+  lDeltaZoom := 1;
+  w := TILE_SIZE;
+  repeat
+    w := w shr 1;
+    dec(ltid.Z);
+    lDeltaZoom := lDeltaZoom shl 1;
+    xfrac := TileId.X / lDeltaZoom; // xfrac, yfrac contains the tile number
+    yfrac := TileId.Y / lDeltaZoom;
+    ltid.X := Trunc(xfrac);
+    ltid.Y := Trunc(yfrac);
+    if InCache(MapProvider, ltid) then
+    begin // We found a tile in the cache that contains the preview
+      xfrac := xfrac - ltid.X; //xfrac and yfrac calculated for the position in the tile from the cache
+      yfrac := yfrac - ltid.Y;
+      px := Trunc(xfrac * TILE_SIZE); //x and y are the percentage of the tile width
+      py := Trunc(yfrac * TILE_SIZE);
+      ARect := Rect(px, py, px+w, py+w);
+      TileID := ltid;
+      Result := true;
+      exit;
+    end;
+  until (w <= 1) or (ltid.Z <= 0);
+end;
+
 function TPictureCache.InCache(MapProvider: TMapProvider;
   const TileId: TTileId): Boolean;
 var

components/lazmapviewer/source/mvde_intfgraphics.pas

@@ -17,7 +17,7 @@ interface
 
 uses
   Classes, SysUtils, Graphics, Types, LclVersion,
-  FPImage, FPCanvas, IntfGraphics,
+  FPImage, FPCanvas, IntfGraphics, LazCanvas,
   mvDrawingEngine;
 
 type
@@ -54,6 +54,7 @@ type
     procedure DrawBitmap(X, Y: Integer; ABitmap: TCustomBitmap;
       UseAlphaChannel: Boolean); override;
     procedure DrawLazIntfImage(X, Y: Integer; AImg: TLazIntfImage); override;
+    procedure DrawScaledLazIntfImage(DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage); override;
     procedure Ellipse(X1, Y1, X2, Y2: Integer); override;
     procedure FillPixels(X1, Y1, X2, Y2: Integer; AColor: TColor); override;
     procedure FillRect(X1, Y1, X2, Y2: Integer); override;
@@ -223,6 +224,39 @@ begin
   {$IFEND}
 end;
 
+{ Scales the rectangle SrcRect of the specified source image (ASrcImg) such
+  that it fits into the rectangle DestRect of the Buffer image. }
+procedure TMvIntfGraphicsDrawingEngine.DrawScaledLazIntfImage(
+  DestRect, SrcRect: TRect; ASrcImg: TLazIntfImage);
+var
+  img: TLazIntfImage;
+  w, h, x, y: Integer;
+begin
+  if FCanvas = nil then
+    exit;
+
+  w := SrcRect.Right - SrcRect.Left;
+  h := SrcRect.Bottom - SrcRect.Top;
+
+  img := TLazIntfImage.Create(0, 0);
+  try
+    img.DataDescription := ASrcImg.DataDescription;
+    img.SetSize(w, h);
+    for y := 0 to h-1 do
+      for x := 0 to w-1 do
+        img.Colors[x, y] := ASrcImg.Colors[SrcRect.Left + x, SrcRect.Top + y];;
+    FCanvas.Interpolation := TFPSharpInterpolation.Create;
+    try
+      FCanvas.StretchDraw(DestRect.Left, DestRect.Top, DestRect.Width, DestRect.Height, img);
+    finally
+      FCanvas.Interpolation.Free;
+      FCanvas.Interpolation := nil;
+    end;
+  finally
+    img.Free;
+  end;
+end;
+
 procedure TMvIntfGraphicsDrawingEngine.Ellipse(X1, Y1, X2, Y2: Integer);
 begin
   if FCanvas <> nil then

components/lazmapviewer/source/mvdrawingengine.pas

@@ -43,6 +43,7 @@ type
     procedure DrawBitmap(X, Y: Integer; ABitmap: TCustomBitmap;
       UseAlphaChannel: Boolean); virtual; abstract;
     procedure DrawLazIntfImage(X, Y: Integer; AImg: TLazIntfImage); virtual; abstract;
+    procedure DrawScaledLazIntfImage(DestRect, SrcRect: TRect; AImg: TLazIntfImage); virtual; abstract;
     procedure Ellipse(X1, Y1, X2, Y2: Integer); virtual; abstract;
     procedure FillPixels(X1, Y1, X2, Y2: Integer; AColor: TColor); virtual; abstract;
     procedure FillRect(X1, Y1, X2, Y2: Integer); virtual; abstract;

components/lazmapviewer/source/mvengine.pas

@@ -30,9 +30,12 @@ const
   EARTH_ECCENTRICITY = sqrt(1 - sqr(EARTH_POLAR_RADIUS / EARTH_EQUATORIAL_RADIUS));
 
 type
-  TDrawTileEvent = Procedure (const TileId: TTileId; X,Y: integer;
+  TDrawTileEvent = procedure (const TileId: TTileId; X,Y: integer;
     TileImg: TLazIntfImage) of object;
 
+  TDrawStretchedTileEvent = procedure (const TileId: TTileId; X,Y: Integer;
+    TileImg: TLazIntfImage; const R: TRect) of object;
+
   TTileIdArray = Array of TTileId;
 
   TDistanceUnits = (duMeters, duKilometers, duMiles);
@@ -62,10 +65,12 @@ type
       FBkColor: TFPColor;
       FCyclic: Boolean;
       FDownloadEngine: TMvCustomDownloadEngine;
+      FDrawPreviewTiles: Boolean;
       FDrawTitleInGuiThread: boolean;
       FOnCenterMove: TNotifyEvent;
       FOnChange: TNotifyEvent;
       FOnDrawTile: TDrawTileEvent;
+      FOnDrawStretchedTile: TDrawStretchedTileEvent;
       FOnZoomChange: TNotifyEvent;
       lstProvider : TStringList;
       Queue : TJobQueue;
@@ -110,6 +115,7 @@ type
       function GetTileName(const Id: TTileId): String;
       procedure evDownload(Data: TObject; Job: TJob);
       procedure TileDownloaded(Data: PtrInt);
+      procedure DrawStretchedTile(const TileId: TTileID; X, Y: Integer; TileImg: TLazIntfImage; const R: TRect);
       Procedure DrawTile(const TileId: TTileId; X,Y: integer; TileImg: TLazIntfImage);
       Procedure DoDrag(Sender: TDragObj);
     public
@@ -147,6 +153,7 @@ type
 
       property BkColor: TFPColor read FBkColor write SetBkColor;
       property Center: TRealPoint read GetCenter write SetCenter;
+      property DrawPreviewTiles : Boolean read FDrawPreviewTiles write FDrawPreviewTiles;
 
     published
       property Active: Boolean read FActive write SetActive default false;
@@ -167,6 +174,7 @@ type
 
       property OnCenterMove: TNotifyEvent read FOnCenterMove write FOnCenterMove;
       property OnChange: TNotifyEvent Read FOnChange write FOnchange; //called when visiable area change
+      property OnDrawStretchedTile: TDrawStretchedTileEvent read FOnDrawStretchedTile write FOnDrawStretchedTile;
       property OnDrawTile: TDrawTileEvent read FOnDrawTile write FOnDrawTile;
       property OnZoomChange: TNotifyEvent read FOnZoomChange write FOnZoomChange;
   end;
@@ -376,6 +384,7 @@ end;
 constructor TMapViewerEngine.Create(aOwner: TComponent);
 begin
   DrawTitleInGuiThread := true;
+  DrawPreviewTiles := true;
   DragObj := TDragObj.Create;
   DragObj.OnDrag := @DoDrag;
   Cache := TPictureCache.Create(self);
@@ -522,6 +531,13 @@ begin
     MoveMapCenter(Sender);
 end;
 
+procedure TMapViewerEngine.DrawStretchedTile(const TileID: TTileID; X, Y: Integer;
+  TileImg: TLazIntfImage; const R: TRect);
+begin
+  if Assigned(FOnDrawStretchedTile) then
+    FOnDrawStretchedTile(TileId, X, Y, TileImg, R);
+end;
+
 procedure TMapViewerEngine.DrawTile(const TileId: TTileId; X, Y: integer;
   TileImg: TLazIntfImage);
 begin
@@ -1038,8 +1054,12 @@ var
   x, y : Integer; //int64;
   Tiles: TTileIdArray = nil;
   iTile: Integer;
+  tile: TTileID;
   numTiles: Integer;
   px, py: Integer;
+  previewDrawn: Boolean;
+  previewImg: TLazIntfImage;
+  R: TRect;
 begin
   if not(Active) then
     Exit;
@@ -1066,9 +1086,24 @@ begin
       // is not valid
       if not Cache.InCache(AWin.MapProvider, Tiles[iTile]) then
       begin
+        previewdrawn := False;
         py := AWin.Y + Y * TILE_SIZE;
         px := AWin.X + X * TILE_SIZE;
-        DrawTile(Tiles[iTile], px, py, nil);
+        if FDrawPreviewTiles then
+        begin
+          if IsValidTile(AWin, Tiles[iTile]) then  // Invalid tiles probably will not be found in the cache
+          begin
+            tile := Tiles[iTile];
+            if Cache.GetPreviewFromCache(AWin.MapProvider, tile, R) then
+            begin
+              Cache.GetFromCache(AWin.MapProvider, tile, previewImg);
+              DrawStretchedTile(Tiles[iTile], px, py, previewImg, R);
+              previewDrawn := true;
+            end;
+          end;
+        end;
+        if not previewDrawn then
+          DrawTile(Tiles[iTile], px, py, nil);  // Draw blank tile if preview cannot be generated
       end;
 
       if IsValidTile(AWin, Tiles[iTile]) then

components/lazmapviewer/source/mvmapviewer.pas

@@ -39,6 +39,7 @@ Type
       FEngine: TMapViewerEngine;
       FBuiltinDrawingEngine: TMvCustomDrawingEngine;
       FDrawingEngine: TMvCustomDrawingEngine;
+      FDrawPreviewTiles: boolean;
       FActive: boolean;
       FGPSItems: TGPSObjectList;
       FPOIImage: TBitmap;
@@ -62,6 +63,7 @@ Type
       function GetCyclic: Boolean;
       function GetDownloadEngine: TMvCustomDownloadEngine;
       function GetDrawingEngine: TMvCustomDrawingEngine;
+      function GetDrawPreviewTiles: Boolean;
       function GetInactiveColor: TColor;
       function GetMapProvider: String;
       function GetOnCenterMove: TNotifyEvent;
@@ -82,6 +84,7 @@ Type
       procedure SetDefaultTrackWidth(AValue: Integer);
       procedure SetDownloadEngine(AValue: TMvCustomDownloadEngine);
       procedure SetDrawingEngine(AValue: TMvCustomDrawingEngine);
+      procedure SetDrawPreviewTiles(AValue: Boolean);
       procedure SetFont(AValue: TFont);
       procedure SetInactiveColor(AValue: TColor);
       procedure SetMapProvider(AValue: String);
@@ -102,6 +105,7 @@ Type
       AsyncInvalidate : boolean;
       procedure ActivateEngine;
       procedure DblClick; override;
+      procedure DoDrawStretchedTile(const TileId: TTileID; X, Y: Integer; TileImg: TLazIntfImage; const R: TRect);
       procedure DoDrawTile(const TileId: TTileId; X,Y: integer; TileImg: TLazIntfImage);
       procedure DoDrawTileInfo(const {%H-}TileID: TTileID; X,Y: Integer);
       function DoMouseWheel(Shift: TShiftState; WheelDelta: Integer;
@@ -148,6 +152,7 @@ Type
       property DefaultTrackWidth: Integer read FDefaultTrackWidth write SetDefaultTrackWidth default 1;
       property DownloadEngine: TMvCustomDownloadEngine read GetDownloadEngine write SetDownloadEngine;
       property DrawingEngine: TMvCustomDrawingEngine read GetDrawingEngine write SetDrawingEngine;
+      property DrawPreviewTiles: Boolean read GetDrawPreviewTiles write SetDrawPreviewTiles default true;
       property Font: TFont read FFont write SetFont stored IsFontStored;
       property Height default 150;
       property InactiveColor: TColor read GetInactiveColor write SetInactiveColor default clWhite;
@@ -343,6 +348,11 @@ begin
     Result := FDrawingEngine;
 end;
 
+function TMapView.GetDrawPreviewTiles: Boolean;
+begin
+  Result := Engine.DrawPreviewTiles;
+end;
+
 function TMapView.GetInactiveColor: TColor;
 begin
   Result := FPColorToTColor(Engine.BkColor);
@@ -454,6 +464,11 @@ begin
   UpdateFont(nil);
 end;
 
+procedure TMapView.SetDrawPreviewTiles(AValue: Boolean);
+begin
+  Engine.DrawPreviewTiles := AValue;
+end;
+
 procedure TMapView.SetFont(AValue: TFont);
 begin
   FFont.Assign(AValue);
@@ -824,21 +839,28 @@ Begin
   AsyncInvalidate := false;
 end;
 
+procedure TMapView.DoDrawStretchedTile(const TileId: TTileId; X, Y: Integer;
+  TileImg: TLazIntfImage; const R: TRect);
+begin
+  if Assigned(TileImg) then
+    DrawingEngine.DrawScaledLazIntfImage(Rect(X, Y, X + TILE_SIZE, Y + TILE_SIZE), R, TileImg)
+  else
+    DrawingEngine.FillPixels(X, Y, X + TILE_SIZE, Y + TILE_SIZE, InactiveColor);
+
+  if FDebugTiles then
+    DoDrawTileInfo(TileID, X, Y);
+
+  DrawObjects(TileId, X, Y, X + TILE_SIZE, Y + TILE_SIZE);
+end;
+
 procedure TMapView.DoDrawTile(const TileId: TTileId; X, Y: integer;
   TileImg: TLazIntfImage);
 begin
-  if Assigned(TileImg) then begin
+  if Assigned(TileImg) then
-    DrawingEngine.DrawLazIntfImage(X, Y, TileImg);
+    DrawingEngine.DrawLazIntfImage(X, Y, TileImg)
-  end
   else
     DrawingEngine.FillPixels(X, Y, X + TILE_SIZE, Y + TILE_SIZE, InactiveColor);
-  {
-    DrawingEngine.BrushColor := InactiveColor;
-    DrawingEngine.BrushStyle := bsSolid;
 
-    DrawingEngine.FillRect(X, Y, X + TILE_SIZE, Y + TILE_SIZE);
-  end;
-   }
   if FDebugTiles then
     DoDrawTileInfo(TileID, X, Y);
 
@@ -888,6 +910,8 @@ begin
   FEngine.CachePath := 'cache/';
   FEngine.CacheOnDisk := true;
   FEngine.OnDrawTile := @DoDrawTile;
+  FEngine.OnDrawStretchedTile := @DoDrawStretchedTile;
+  FEngine.DrawPreviewTiles := True;
   FEngine.DrawTitleInGuiThread := false;
   FEngine.DownloadEngine := FBuiltinDownloadEngine;
   FEngine.ZoomToCursor := True;