lazmapviewer: Improved drawing code. Extend both fulldemo projects by map layers. Patch by Yuliyan Ivanov. Issue #39063.

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@9150 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/lazmapviewer/examples/fulldemo/main.pas

@@ -7,7 +7,7 @@ interface
 uses
   Classes, SysUtils, Types, Forms, Controls, Graphics, Dialogs, ExtCtrls,
   StdCtrls, ComCtrls, Buttons, IntfGraphics, ColorBox, Spin, PrintersDlgs,
-  mvGeoNames, mvMapViewer, mvTypes, mvGpsObj, mvDrawingEngine;
+  mvGeoNames, mvMapViewer, mvTypes, mvGpsObj, mvDrawingEngine, Grids;
 
 type
 
@@ -81,6 +81,10 @@ type
     PrintDialog1: TPrintDialog;
     rgPOIMode: TRadioGroup;
     seProxyPort: TSpinEdit;
+    sgLayers: TStringGrid;
+    rgDrawMode: TRadioGroup;
+    lblOpacity: TLabel;
+    tbOpacity: TTrackBar;
     ZoomTrackBar: TTrackBar;
     procedure BtnGoToClick(Sender: TObject);
     procedure BtnLoadGPXFileClick(Sender: TObject);
@@ -118,7 +122,14 @@ type
     procedure MapViewZoomChange(Sender: TObject);
     procedure BtnLoadMapProvidersClick(Sender: TObject);
     procedure BtnSaveMapProvidersClick(Sender: TObject);
+    procedure rgDrawModeSelectionChanged(Sender: TObject);
     procedure rgPOIModeClick(Sender: TObject);
+    procedure sgLayersCheckboxToggled(sender: TObject; aCol, aRow: Integer;
+      aState: TCheckboxState);
+    procedure sgLayersEditingDone(Sender: TObject);
+    procedure sgLayersSelection(Sender: TObject; aCol, aRow: Integer);
+    procedure tbOpacityChange(Sender: TObject);
+    procedure UpdateLayers;
     procedure ZoomTrackBarChange(Sender: TObject);
 
   private
@@ -160,9 +171,11 @@ const
   MAX_LOCATIONS_HISTORY = 50;
   MAP_PROVIDER_FILENAME = 'map-providers.xml';
   USE_DMS = true;
+  _TILELAYERS_ID_ = 42;
 
 var
   PointFormatSettings: TFormatsettings;
+  TileLayer: array[0..9] of TGPSTileLayer;
 
 function CalcIniName: String;
 begin
@@ -183,6 +196,7 @@ begin
       MapView.GetMapProviders(CbProviders.Items);
       CbProviders.ItemIndex := 0;
       MapView.MapProvider := CbProviders.Text;
+      sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
     end else
       ShowMessage(msg);
   end;
@@ -193,6 +207,12 @@ begin
   MapView.Engine.WriteProvidersToXML(Application.Location + MAP_PROVIDER_FILENAME);
 end;
 
+procedure TMainForm.rgDrawModeSelectionChanged(Sender: TObject);
+begin
+  TileLayer[Pred(sgLayers.Row)].DrawMode := TItemDrawMode(rgDrawMode.ItemIndex);
+  MapView.Redraw;
+end;
+
 procedure TMainForm.BtnSearchClick(Sender: TObject);
 begin
   ClearFoundLocations;
@@ -349,11 +369,13 @@ end;
 procedure TMainForm.cbCyclicViewChange(Sender: TObject);
 begin
   MapView.Cyclic := cbCyclicView.Checked;
+  UpdateLayers;
 end;
 
 procedure TMainForm.CbDebugTilesChange(Sender: TObject);
 begin
   MapView.DebugTiles := CbDebugTiles.Checked;
+  MapView.Invalidate;
 end;
 
 procedure TMainForm.CbDoubleBufferChange(Sender: TObject);
@@ -423,6 +445,7 @@ end;
 procedure TMainForm.CbUseThreadsChange(Sender: TObject);
 begin
   MapView.UseThreads := CbUseThreads.Checked;
+  UpdateLayers;
 end;
 
 procedure TMainForm.CbDistanceUnitsChange(Sender: TObject);
@@ -458,6 +481,7 @@ var
   homeDir: String;
   cacheDir: String;
   fn: String;
+  I: Integer;
 begin
   cInputQueryEditSizePercents := 0;
 
@@ -483,6 +507,7 @@ begin
   MapView.CachePath := cacheDir;
   MapView.GetMapProviders(CbProviders.Items);
   CbProviders.ItemIndex := CbProviders.Items.IndexOf(MapView.MapProvider);
+  sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
   MapView.DoubleBuffered := true;
   MapView.Zoom := 1;
   CbZoomToCursor.Checked := MapView.ZoomToCursor;
@@ -499,12 +524,38 @@ begin
   InfoViewportHeight.Caption := '';
   GPSPointInfo.caption := '';
 
+  for I := 0 to High(TileLayer) do
+  begin
+    TileLayer[I] := TGPSTileLayer.Create;
+    with TileLayer[I] do
+    begin
+      Visible := False;
+      UseThreads := MapView.UseThreads;
+      DrawMode := idmUseOpacity;
+      Opacity := 0.25;
+      case I of
+        0: MapProvider := 'Google Satellite Only';
+        1: MapProvider := 'Google Terrain';
+        2: MapProvider := 'Maps For Free';
+      otherwise
+        MapProvider := '';
+      end;
+    end;
+    sgLayers.Cells[1, I + 1] := TileLayer[I].Visible.ToString;
+    sgLayers.Cells[2, I + 1] := TileLayer[I].MapProvider;
+    MapView.GPSLayer[I].Add(TileLayer[I], _TILELAYERS_ID_);
+  end;
+
   ReadFromIni;
 end;
 
 procedure TMainForm.FormDestroy(Sender: TObject);
+var
+  I: Integer;
 begin
   WriteToIni;
+  for I := 0 to High(TileLayer) do
+    MapView.GPSLayer[I].Delete(TileLayer[I]);
   ClearFoundLocations;
   FreeAndNil(POIImage)
 end;
@@ -742,6 +793,7 @@ begin
       MapView.Engine.ClearMapProviders;
       MapView.Engine.RegisterProviders;
       MapView.GetMapProviders(CbProviders.Items);
+      sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
     end;
 
     R := Screen.DesktopRect;
@@ -829,6 +881,47 @@ begin
   end;
 end;
 
+procedure TMainForm.sgLayersCheckboxToggled(sender: TObject; aCol,
+  aRow: Integer; aState: TCheckboxState);
+begin
+  TileLayer[Pred(sgLayers.Row)].Visible := (aState = cbChecked);
+  MapView.Redraw;
+end;
+
+procedure TMainForm.sgLayersEditingDone(Sender: TObject);
+var
+  S: String;
+begin
+  if sgLayers.Col <> 2 then
+    Exit;
+  S := sgLayers.Cells[sgLayers.Col, sgLayers.Row];
+  TileLayer[Pred(sgLayers.Row)].MapProvider := S;
+  sgLayers.Cells[sgLayers.Col, sgLayers.Row] := S;
+  MapView.Redraw;
+end;
+
+procedure TMainForm.sgLayersSelection(Sender: TObject; aCol, aRow: Integer);
+begin
+  rgDrawMode.ItemIndex := Ord(TileLayer[Pred(ARow)].DrawMode);
+  tbOpacity.Position := Round(TileLayer[Pred(ARow)].Opacity * 100);
+end;
+
+procedure TMainForm.tbOpacityChange(Sender: TObject);
+begin
+  TileLayer[Pred(sgLayers.Row)].Opacity := tbOpacity.Position / 100;
+  MapView.Redraw;
+end;
+
+procedure TMainForm.UpdateLayers;
+var
+  TL: TGPSTileLayer;
+begin
+  // Notify tile layers for drawing engine change, it must be done implicitly
+  // but there is no other mechanism for now
+  for TL in TileLayer do
+    TL.ParentViewChanged;
+end;
+
 procedure TMainForm.UpdateCoords(X, Y: Integer);
 var
   rPt: TRealPoint;

components/lazmapviewer/examples/fulldemo_with_addons/main.pas

@@ -6,7 +6,7 @@ interface
 
 uses
   Classes, SysUtils, Types, Forms, Controls, Graphics, Dialogs,
-  ExtCtrls, StdCtrls, ComCtrls, Buttons, IntfGraphics, ColorBox, Spin,
+  ExtCtrls, StdCtrls, ComCtrls, Buttons, IntfGraphics, ColorBox, Spin, Grids,
   mvGeoNames, mvMapViewer, mvTypes, mvGpsObj, mvDrawingEngine,
   mvDE_RGBGraphics, mvDE_BGRA, mvDLEFPC, mvDLEWin, mvDLESynapse;
 
@@ -16,6 +16,7 @@ type
 
   TMainForm = class(TForm)
     Bevel1: TBevel;
+    Bevel2: TBevel;
     BtnSearch: TButton;
     BtnGoTo: TButton;
     BtnGPSPoints: TButton;
@@ -27,6 +28,8 @@ type
     CbFoundLocations: TComboBox;
     CbLocations: TComboBox;
     CbProviders: TComboBox;
+    lblOpacity: TLabel;
+    rgDrawMode: TRadioGroup;
     rbProxyData: TRadioButton;
     rbSystemProxy: TRadioButton;
     CbUseThreads: TCheckBox;
@@ -83,6 +86,9 @@ type
     PgConfig: TTabSheet;
     rbNoProxy: TRadioButton;
     seProxyPort: TSpinEdit;
+    pgLayers: TTabSheet;
+    sgLayers: TStringGrid;
+    tbOpacity: TTrackBar;
     ZoomTrackBar: TTrackBar;
     procedure BtnGoToClick(Sender: TObject);
     procedure BtnLoadGPXFileClick(Sender: TObject);
@@ -121,6 +127,13 @@ type
     procedure BtnLoadMapProvidersClick(Sender: TObject);
     procedure BtnSaveMapProvidersClick(Sender: TObject);
     procedure rbProxyChange(Sender: TObject);
+    procedure rgDrawModeSelectionChanged(Sender: TObject);
+    procedure sgLayersCheckboxToggled(Sender: TObject; aCol, aRow: Integer;
+      aState: TCheckboxState);
+    procedure sgLayersEditingDone(Sender: TObject);
+    procedure sgLayersSelection(Sender: TObject; aCol, aRow: Integer);
+    procedure tbOpacityChange(Sender: TObject);
+    procedure UpdateLayers;
     procedure ZoomTrackBarChange(Sender: TObject);
 
   private
@@ -167,9 +180,11 @@ const
   MAX_LOCATIONS_HISTORY = 50;
   MAP_PROVIDER_FILENAME = 'map-providers.xml';
   USE_DMS = true;
+  _TILELAYERS_ID_ = 42;
 
 var
   PointFormatSettings: TFormatsettings;
+  TileLayer: array[0..9] of TGPSTileLayer;
 
 
 function CalcIniName: String;
@@ -177,7 +192,6 @@ begin
   Result := ChangeFileExt(Application.ExeName, '.ini');
 end;
 
-
 { TMainForm }
 
 procedure TMainForm.BtnLoadMapProvidersClick(Sender: TObject);
@@ -191,6 +205,7 @@ begin
       MapView.GetMapProviders(CbProviders.Items);
       CbProviders.ItemIndex := 0;
       MapView.MapProvider := CbProviders.Text;
+      sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
     end else
       ShowMessage(msg);
   end;
@@ -206,6 +221,53 @@ begin
   UpdateDownloadEngineProxy;
 end;
 
+procedure TMainForm.rgDrawModeSelectionChanged(Sender: TObject);
+begin
+  TileLayer[Pred(sgLayers.Row)].DrawMode := TItemDrawMode(rgDrawMode.ItemIndex);
+  MapView.Redraw;
+end;
+
+procedure TMainForm.sgLayersCheckboxToggled(Sender: TObject; aCol,
+  aRow: Integer; aState: TCheckboxState);
+begin
+  TileLayer[Pred(sgLayers.Row)].Visible := (aState = cbChecked);
+  MapView.Redraw;
+end;
+
+procedure TMainForm.sgLayersEditingDone(Sender: TObject);
+var
+  S: String;
+begin
+  if sgLayers.Col <> 2 then
+    Exit;
+  S := sgLayers.Cells[sgLayers.Col, sgLayers.Row];
+  TileLayer[Pred(sgLayers.Row)].MapProvider := S;
+  sgLayers.Cells[sgLayers.Col, sgLayers.Row] := S;
+  MapView.Redraw;
+end;
+
+procedure TMainForm.sgLayersSelection(Sender: TObject; aCol, aRow: Integer);
+begin
+  rgDrawMode.ItemIndex := Ord(TileLayer[Pred(ARow)].DrawMode);
+  tbOpacity.Position := Round(TileLayer[Pred(ARow)].Opacity * 100);
+end;
+
+procedure TMainForm.tbOpacityChange(Sender: TObject);
+begin
+  TileLayer[Pred(sgLayers.Row)].Opacity := tbOpacity.Position / 100;
+  MapView.Redraw;
+end;
+
+procedure TMainForm.UpdateLayers;
+var
+  TL: TGPSTileLayer;
+begin
+  // Notify tile layers for drawing engine change, it must be done implicitly
+  // but there is no other mechanism for now
+  for TL in TileLayer do
+    TL.ParentViewChanged;
+end;
+
 procedure TMainForm.BtnSearchClick(Sender: TObject);
 begin
   ClearFoundLocations;
@@ -284,6 +346,7 @@ end;
 procedure TMainForm.CbDebugTilesChange(Sender: TObject);
 begin
   MapView.DebugTiles := CbDebugTiles.Checked;
+  MapView.Invalidate;
 end;
 
 procedure TMainForm.CbDownloadEngineChange(Sender: TObject);
@@ -328,6 +391,7 @@ begin
          MapView.DrawingEngine := FBGRADrawingEngine;
        end;
   end;
+  UpdateLayers;
 end;
 
 procedure TMainForm.CbDoubleBufferChange(Sender: TObject);
@@ -390,6 +454,7 @@ end;
 procedure TMainForm.CbUseThreadsChange(Sender: TObject);
 begin
   MapView.UseThreads := CbUseThreads.Checked;
+  UpdateLayers;
 end;
 
 procedure TMainForm.CbDistanceUnitsChange(Sender: TObject);
@@ -406,6 +471,7 @@ end;
 procedure TMainForm.CbCyclicChange(Sender: TObject);
 begin
   MapView.Cyclic := CbCyclic.Checked;
+  UpdateLayers;
 end;
 
 procedure TMainForm.clbBackColorColorChanged(Sender: TObject);
@@ -430,6 +496,7 @@ var
   fn: String;
   homeDir: String;
   cacheDir: String;
+  I: Integer;
 begin
   cInputQueryEditSizePercents := 0;
 
@@ -454,6 +521,7 @@ begin
   end;
   MapView.CachePath := cacheDir;
   MapView.GetMapProviders(CbProviders.Items);
+  sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
   CbProviders.ItemIndex := CbProviders.Items.IndexOf(MapView.MapProvider);
   MapView.DoubleBuffered := true;
   MapView.Zoom := 1;
@@ -471,10 +539,34 @@ begin
   InfoViewportHeight.Caption := '';
   GPSPointInfo.Caption := '';
 
+  for I := 0 to High(TileLayer) do
+  begin
+    TileLayer[I] := TGPSTileLayer.Create;
+    with TileLayer[I] do
+    begin
+      Visible := False;
+      UseThreads := MapView.UseThreads;
+      DrawMode := idmUseOpacity;
+      Opacity := 0.25;
+      case I of
+        0: MapProvider := 'Google Satellite Only';
+        1: MapProvider := 'Google Terrain';
+        2: MapProvider := 'Maps For Free';
+      otherwise
+        MapProvider := '';
+      end;
+    end;
+    sgLayers.Cells[1, I + 1] := TileLayer[I].Visible.ToString;
+    sgLayers.Cells[2, I + 1] := TileLayer[I].MapProvider;
+    MapView.GPSLayer[I].Add(TileLayer[I], _TILELAYERS_ID_);
+  end;
+
   ReadFromIni;
 end;
 
 procedure TMainForm.FormDestroy(Sender: TObject);
+var
+  I: Integer;
 begin
   WriteToIni;
   ClearFoundLocations;
@@ -629,6 +721,7 @@ begin
       MapView.Engine.ClearMapProviders;
       MapView.Engine.RegisterProviders;
       MapView.GetMapProviders(CbProviders.Items);
+      sgLayers.Columns[1].PickList.Assign(CbProviders.Items);
     end;
 
     R := Screen.DesktopRect;

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

@@ -69,7 +69,6 @@ type
     procedure SetFontStyle(AValue: TFontStyles); override;
     procedure SetPenColor(AValue: TColor); override;
     procedure SetPenWidth(AValue: Integer); override;
-
   public
     destructor Destroy; override;
     procedure CreateBuffer(AWidth, AHeight: Integer); override;

components/lazmapviewer/source/mvengine.pas

@@ -36,6 +36,8 @@ type
   TDrawStretchedTileEvent = procedure (const TileId: TTileId; X,Y: Integer;
     TileImg: TPictureCacheItem; const R: TRect) of object;
 
+  TEraseBackgroundEvent = procedure (const R: TRect) of Object;
+
   TTileDownloadedEvent = procedure (const TileId: TTileId) of object;
 
   TTileIdArray = Array of TTileId;
@@ -74,6 +76,7 @@ type
       FOnChange: TNotifyEvent;
       FOnDrawTile: TDrawTileEvent;
       FOnDrawStretchedTile: TDrawStretchedTileEvent;
+      FOnEraseBackground: TEraseBackgroundEvent;
       FOnTileDownloaded: TTileDownloadedEvent;
       FOnZoomChange: TNotifyEvent;
       lstProvider : TStringList;
@@ -123,6 +126,7 @@ type
       function GetTileName(const Id: TTileId): String;
       procedure evDownload(Data: TObject; Job: TJob);
       procedure TileDownloaded(Data: PtrInt);
+      procedure EraseBackground(const R: TRect);
       procedure DrawTileFromCache(constref ATile: TTileId; constref AWin: TMapWindow);
       procedure DrawStretchedTile(const TileId: TTileID; X, Y: Integer; TileImg: TPictureCacheItem; const R: TRect);
       Procedure DrawTile(const TileId: TTileId; X,Y: integer; TileImg: TPictureCacheItem);
@@ -194,6 +198,7 @@ type
       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 OnEraseBackground: TEraseBackgroundEvent read FOnEraseBackground write FOnEraseBackground;
       property OnTileDownloaded: TTileDownloadedEvent read FOnTileDownloaded write FOnTileDownloaded;
       property OnZoomChange: TNotifyEvent read FOnZoomChange write FOnZoomChange;
   end;
@@ -357,25 +362,25 @@ function TMapViewerEngine.CalculateVisibleTiles(const aWin: TMapWindow; out
   Area: TArea): Boolean;
 var
   MaxX, MaxY, startX, startY: int64;
-  WorldSize: Int64;
+  WorldMax: Int64;
 begin
   Area := Default(TArea);
-  Result := True;
+  Result := (aWin.X <= 0) and (aWin.Y <= 0);
-  WorldSize := 1 shl AWin.Zoom;
+  WorldMax := 1 shl AWin.Zoom - 1;
   MaxX := Int64(aWin.Width) div TILE_SIZE + 1;
   MaxY := Int64(aWin.Height) div TILE_SIZE + 1;
-  if (MaxX > WorldSize) or (MaxY > WorldSize) then
+  if (MaxX > WorldMax) or (MaxY > WorldMax) then
   begin
     Result := False;
-    MaxX := Min(WorldSize - 1, MaxX);
+    MaxX := Min(WorldMax, MaxX);
-    MaxY := Min(WorldSize - 1, MaxY);
+    MaxY := Min(WorldMax, MaxY);
   end;
   startX := -aWin.X div TILE_SIZE;
   startY := -aWin.Y div TILE_SIZE;
   if (startX < 0) or (startY < 0) then
   begin
-    startX := Max(0, -aWin.X div TILE_SIZE);
+    startX := Max(0, startX);
-    startY := Max(0, -aWin.Y div TILE_SIZE);
+    startY := Max(0, startY);
     Result := False;
   end;
   Area.Left := startX;
@@ -1025,13 +1030,27 @@ var
     end;
   end;
 
-  procedure EraseBackground;
+  procedure EraseAround;
   var
-    I, J: Integer;
+    T, L, B, R: Integer;
   begin
-    for J := 0 to (AWin.Height div TILE_SIZE) + 1 do
+    T := -AWin.Y div TILE_SIZE - Max(0, Sign(AWin.Y));
-      for I := 0 to (AWin.Width div TILE_SIZE) + 1 do
+    B := T + AWin.Height div TILE_SIZE + 1;
-        DrawTile(tile, I * TILE_SIZE, J * TILE_SIZE, Nil);
+    L := -AWin.X div TILE_SIZE - Max(0, Sign(AWin.X));
+    R := L + AWin.Width div TILE_SIZE + 1;
+    if T < TilesVis.top then  // Erase above top
+      EraseBackground(Rect(0, 0, AWin.Width, AWin.Y + TilesVis.top * TILE_SIZE));
+    if L < TilesVis.left then // Erase on the left
+      EraseBackground(Rect(0, AWin.Y + TilesVis.top * TILE_SIZE,
+        AWin.X + TilesVis.left * TILE_SIZE,
+        AWin.Y + (TilesVis.bottom + 1) * TILE_SIZE));
+    if R > TilesVis.right then // Erase on the right
+      EraseBackground(Rect(AWin.X + (TilesVis.right + 1) * TILE_SIZE,
+        AWin.Y + TilesVis.top * TILE_SIZE, AWin.Width,
+        AWin.Y + (TilesVis.bottom + 1) * TILE_SIZE));
+    if B > TilesVis.bottom then // Erase below
+      EraseBackground(Rect(0, AWin.Y + (TilesVis.bottom + 1) * TILE_SIZE,
+        AWin.Width, AWin.Height));
   end;
 
 begin
@@ -1039,7 +1058,7 @@ begin
     Exit;
 
   if not CalculateVisibleTiles(AWin, TilesVis) then
-    EraseBackground;
+    EraseAround;
   SetLength(Tiles, (TilesVis.Bottom - TilesVis.Top + 1) * (TilesVis.Right - TilesVis.Left + 1));
   iTile := Low(Tiles);
   numTiles := 1 shl AWin.Zoom;
@@ -1273,6 +1292,12 @@ begin
   end;
 end;
 
+procedure TMapViewerEngine.EraseBackground(const R: TRect);
+begin
+  if Assigned(FOnEraseBackground) then
+      FOnEraseBackground(R);
+end;
+
 procedure TMapViewerEngine.DrawTileFromCache(constref ATile: TTileId; constref
   AWin: TMapWindow);
 var

components/lazmapviewer/source/mvmapviewer.pas

@@ -111,6 +111,7 @@ Type
       procedure DoDrawStretchedTile(const TileId: TTileID; X, Y: Integer; TileImg: TPictureCacheItem; const R: TRect);
       procedure DoDrawTile(const TileId: TTileId; X,Y: integer; TileImg: TPictureCacheItem);
       procedure DoDrawTileInfo(const {%H-}TileID: TTileID; X,Y: Integer);
+      procedure DoEraseBackground(const R: TRect);
       procedure DoTileDownloaded(const TileId: TTileId);
       function DoMouseWheel(Shift: TShiftState; WheelDelta: Integer;
         MousePos: TPoint): Boolean; override;
@@ -713,20 +714,35 @@ begin
 end;
 
 procedure TMapView.Paint;
-begin
+
-  inherited Paint;
+  procedure Inactive;
-  if IsActive then
-  begin
-    Engine.Redraw;
-    DrawObjects(Default(TTileId), 0, 0, Canvas.Width, Canvas.Height);
-    DrawingEngine.PaintToCanvas(Canvas);
-  end
-  else
   begin
     Canvas.Brush.Color := InactiveColor;
     Canvas.Brush.Style := bsSolid;
     Canvas.FillRect(0, 0, ClientWidth, ClientHeight);
   end;
+
+  procedure Redrw;
+  begin
+    Engine.Redraw;
+    DrawObjects(Default(TTileId), 0, 0, Canvas.Width, Canvas.Height);
+    DrawingEngine.PaintToCanvas(Canvas);
+  end;
+
+  procedure Drag;
+  begin
+    // Placeholder for dragging visuals
+    Redrw;
+  end;
+
+begin
+  inherited Paint;
+  if IsActive
+    then if Engine.InDrag
+      then Drag
+      else Redrw
+    else
+      Inactive;
 end;
 
 procedure TMapView.OnGPSItemsModified(Sender: TObject; objs: TGPSObjList;
@@ -1010,6 +1026,11 @@ begin
   DrawingEngine.Line(X, Y + TILE_SIZE, X + TILE_SIZE, Y + TILE_SIZE);
 end;
 
+procedure TMapView.DoEraseBackground(const R: TRect);
+begin
+  DrawingEngine.FillPixels(R.Left, R.Top, R.Right, R.Bottom, InactiveColor);
+end;
+
 procedure TMapView.DoTileDownloaded(const TileId: TTileId);
 begin
   // TODO: Include tile information to optimize redraw.
@@ -1055,6 +1076,7 @@ begin
   FEngine.CacheOnDisk := true;
   FEngine.OnDrawTile := @DoDrawTile;
   FEngine.OnDrawStretchedTile := @DoDrawStretchedTile;
+  FEngine.OnEraseBackground := @DoEraseBackground;
   FEngine.OnTileDownloaded := @DoTileDownloaded;
   FEngine.DrawPreviewTiles := True;
   FEngine.DrawTitleInGuiThread := false;