Block preview in a gallery

[NicolasBBS]

Hello,
I'm trying to create a gallery in my application. This gallery should display thumbnails for each block found into a DXF/DWG File.

First solution I tried :
Create a new TsgCADImage for each thumbnail, copy the block entity to it from the original TsgCADImage (using assignEntity, and also copy all entities of the original block...), create an insert and assign the new TsgCADImage to a TImage.picture.graphic property.
It works quite correctly, although I can't free the original TsgCADImage before the new ones. After having read this forum I think some objects of the original CADImage are linked to my new entities, and should be copied manually if I wanted to solve this problem.
But the main problem of this solution is the amount of memory it takes. For an original CADImage which contains about 70 blocks and takes about 4 Mo into memory, The creation of 70 new CADImages with one block each one takes about 250 Mo ! And the time it takes to be displayed at screen is rather long. So I decided to search for another solution.

Second solution I tried :
Create only one TsgCADImage to load the file, and find a way to display a block onto a canvas. I found a procedure DrawRect in TsgCADImage, so I tried to create another procedure TsgCADImage.drawBlock, with the same principle. In fact I needed to have only one block inserted into my drawing, and then I could call draw like it is done into DrawRect. So this is my code :

Code: Select all

procedure TsgCADImage.DrawBlock(canvas:TCanvas; Block: TsgDXFBlock; DestRect: TRect);
var
  vInsert: TsgDXFInsert;
  vLayout: TsgDXFLayout;
  oldLayout: TsgDXFLayout;
  oRatio,dRatio,l:real;
begin
  if FCurrentLayout = nil then Exit;
  try
     oldLayout:=CurrentLayout;
     vLayout:=TsgDXFLayout.Create;
     Converter.AddLayout(vLayout);
     CurrentLayout:=vLayout;
     vInsert:=TsgDXFInsert.Create;
     if assigned(Converter.OnCreate) then
        Converter.OnCreate(vInsert);
     vInsert.Block:=Block;
     vInsert.Point := MakeFPoint(0, 0, 0);
     CurrentLayout.AddEntity(vInsert);
     converter.Loads(vInsert);
     GetExtents;
     oRatio:=(Extents.Right-Extents.Left)/(Extents.Top-Extents.Bottom);
     dRatio:=(destRect.Right-destRect.Left)/(destRect.Bottom-destRect.Top);
     if dRatio>oRatio then
     begin
        l:=(destRect.Bottom-destRect.Top)*oRatio;
        destRect.Left:=destRect.Left + round((destRect.Right-destRect.Left-l)/2);
        destRect.Right:=destRect.Right - round((destRect.Right-destRect.Left-l)/2);
     end
     else
     begin
        l:=(destRect.Right-destRect.Left)/oRatio;
        destRect.top:=destRect.top + round((destRect.Bottom-destRect.top-l)/2);
        destRect.Bottom:=destRect.Bottom - round((destRect.Bottom-destRect.top-l)/2);
     end;
     Draw(canvas, DestRect);

     converter.RemoveEntity(vInsert,true);
     CurrentLayout:=oldLayout;
     converter.DeleteLayout(vLayout);
  finally
  end;
end;

With this method, my thumbnails are drawn rather quickly, and it takes a negligible amount of memory.
But when I free the CADImage, I have some access violation in TsgDXFConverter.Clear procedure, into the call to FBlocks.Clear ; it seems like blocks are already released.

Just to see what I do with this procedure, this my calling code :

Code: Select all

         for ioBlock:=0 to sgImg.Converter.Counts[csBlocks]-1 do
         begin
            oblock:=sgImg.Converter.Blocks[ioBlock];
            if (not oBlock.SpecPaperSpace) or (oBlock.name='*[Model]') then
            begin
               panel:=AdvPanelGroup1.Panels[icBlock]; //the exact number of panels are created earlier in my code
               img:=TImage.Create(panel);
               img.Parent:=panel;
               Img.Align:=alClient;
               sgImg.DrawBlock(img.canvas,oBlock,rect(0,0,img.width,img.height));
               inc(icBlock);
            end;
         end;

Third solution :
I think it would be possible to make the same drawing without creating a layout and an insert, but I didn't reach to make something work correctly this way.
This is what I tried :
- create a property FDrawBlock:TsgDXFBlock in TsgCADImage.
- assign this property with the block before calling Draw into the procedure DrawBlock, and clear this property after.
- in the procedure TsgCADImage.Draw, if property FDrawBlock is assigned, iterate through the block intead of iterate through currentLayout.
- in the procedure TsgCADImage.Draw, modify evaluation expression for vRectVisible : vRectVisible := (FDrawBlock<>nil) or IsEntityInRectVisible(vTmpIRect);
It works only if layout and insert are created into the procedure DrawBlock, or else I've a stack overflow into realLayer function.

So please could you help me to make the second or third solution work ? I think I'm near my goal, but now I have no more idea.

[support]

Hello Nicolas.
The second solution that you tried to realize looks most correct. However we're not sure why special DrawBlock procedure. You can use extents for the new layout if a single block reference added onto it. Values in TsgDXFInsert.Box structure do the same. Alternatively you can create a new TsgCADImage object and add block references onto it, each for separate layout. Such approach won't consume much memory unlike creating new TsgCADImage object for each block reference.
The access violation error can be caused by incorrect CADImage freeing. Which code you use to free this object? Have you called TsgDXFConverter.Clear from code or it called internally?

Alexander.

[NicolasBBS]

Thank you Alexander for your answer.
This how I create, use and free CADImage (I think the access violation is the most important problem to solve) :

Code: Select all

procedure TFrameDXF.DrawVignettes(fileName:string);
//var (...)
begin
    sgImg:=nil;
    vFileExt := ExtractFileExt(LowerCase(FileName));
    case StrIndex(vFileExt, Exts) of
      0:	sgImg := TsgCADdxfImage.Create;
      1:	sgImg := TsgDWGImage.Create;
      2:     sgImg := TsgSVGImage.Create;
      3:     sgImg := TsgCGMImage.Create;
    end;
    if sgImg <> nil then
    begin
      sgImg.Converter.NumberOfPartsInSpline := 16;
      sgImg.Converter.NumberOfPartsInCircle := 16;
      sgImg.LoadFromFile(FileName);

   //Count blocks and create panels
   //(...)

   //Draw blocks
      if nbBlocks>0 then
      begin
         icBlock:=0;
         for ioBlock:=0 to sgImg.Converter.Counts[csBlocks]-1 do
         begin
            oblock:=sgImg.Converter.Blocks[ioBlock];
            if (not oBlock.SpecPaperSpace) or (oBlock.name='*[Model]') then
            begin
               panel:=AdvPanelGroup1.Panels[icBlock];
               img:=TImage.Create(panel);
               img.Parent:=panel;
               Img.Align:=alClient;
               sgImg.DrawBlock(img.canvas{.Handle},oBlock,rect(0,0,img.width,img.height));
               inc(icBlock);
            end;
         end;
    end;
end;

procedure TFrameDXF.clearVignettes;
begin
   freeAndNil(sgImg);
   AdvPanelGroup1.BeginUpdate;
   AdvPanelGroup1.Clear;
   AdvPanelGroup1.EndUpdate;
end;

procedure TFrameDXF.ShellTreeView1Change(Sender: TObject; Node: TTreeNode);
var Xext:string;
    folder:TShellFolder;
begin
   clearVignettes;
   Xext:=ExtractFileExt(Node.Text);
   if SameText(Xext,'.dxf') or SameText(Xext,'.dwg') then
   begin
      folder:=TShellFolder(Node.Data);
      DrawVignettes(folder.PathName);
   end;
end;

The access violation occurs after having displayed a first file, when trying to select and display a second file. TsgDXFConverter.Clear is called internally, this my call stack :
- ...
- FreeAndNil(FBlockRecord)
- TsgDXFBlock.destroy
- TObject.free
- TsgDXFGroup.Clear
- TsgDXFTable.Clear
- TsgDXFConverter.Clear --->FBlocks.clear;
- TsgDXFConverter.Destroy
- TsgDWGConverter.Destroy
- TsgDXFConverter.release
- TsgCADImage.Destroy

Note that when I put a breakpoint into TsgDXFBlock.destroy, I see a lot of blocks destroying correctly before having a crash.
I don't understand what do you mean in your other sentences, so I'll ask new questions, but I think it is less important :

However we're not sure why special DrawBlock procedure.

What do you mean ? I could have put my code externally from TsgCADImage ? Yes if Draw was public. But I thought you could be interested by my function and add it to your native code...

You can use extents for the new layout if a single block reference added onto it. Values in TsgDXFInsert.Box structure do the same.

Yes but does it have any importance ? Is my code lower ? Do you mean there is no need to call GetExtents ?

Alternatively you can create a new TsgCADImage object and add block references onto it, each for separate layout.

Ok but I'd prefer my second solution if we can solve the access violation, it looks more elegant. And I'm not sure I'll not have the same access violation when freeing the second TsgCADImage...

So I hope you will find why I have this access violation... I cross my fingers ! Thanks.

[NicolasBBS]

Hello,

Please note that if I keep only this part of my code into DrawBlock, I do not have any access violation (but it draws the complete model of course...) :

Code: Select all

procedure TsgCADImage.DrawBlock(canvas:TCanvas; Block: TsgDXFBlock; DestRect: TRect);
var
  vInsert: TsgDXFInsert;
  vLayout: TsgDXFLayout;
  oldLayout: TsgDXFLayout;
  oRatio,dRatio,l:real;
begin
  if FCurrentLayout = nil then Exit;
  try
//     oldLayout:=CurrentLayout;
//     vLayout:=TsgDXFLayout.Create;
//     Converter.AddLayout(vLayout);
//     CurrentLayout:=vLayout;
//     vInsert:=TsgDXFInsert.Create;
//     if assigned(Converter.OnCreate) then
//        Converter.OnCreate(vInsert);
//     vInsert.Block:=Block;
//     vInsert.Point := MakeFPoint(0, 0, 0);
//     CurrentLayout.AddEntity(vInsert);
//     converter.Loads(vInsert);
     GetExtents;
     oRatio:=(Extents.Right-Extents.Left)/(Extents.Top-Extents.Bottom);
     dRatio:=(destRect.Right-destRect.Left)/(destRect.Bottom-destRect.Top);
     if dRatio>oRatio then
     begin
        l:=(destRect.Bottom-destRect.Top)*oRatio;
        destRect.Left:=destRect.Left + round((destRect.Right-destRect.Left-l)/2);
        destRect.Right:=destRect.Right - round((destRect.Right-destRect.Left-l)/2);
     end
     else
     begin
        l:=(destRect.Right-destRect.Left)/oRatio;
        destRect.top:=destRect.top + round((destRect.Bottom-destRect.top-l)/2);
        destRect.Bottom:=destRect.Bottom - round((destRect.Bottom-destRect.top-l)/2);
     end;
     Draw(canvas, DestRect);

//     converter.RemoveEntity(vInsert,true);
//     CurrentLayout:=oldLayout;
//     converter.DeleteLayout(vLayout);
  finally
  end;
end;

And if I remove only the last 3 lines (removeEntity, DeleteLayout), I have the access violation. So I think the way I add the layout and the insert is not correct.

[support]

Hello Nicolas.
The problem depends on deleting a layout that was created. When you create a layout a block also created for the new layout and added to Blocks section. This block not deleted with DeleteLayout method. So the error appears when a new layout created for a second drawing. We have created a simple demo project that visualizes blocks from imported drawing, please check it. The library files must be copied to Lib folder.
Generally there is no need to create new layout each time you display a next block. You can just clear entities and add a new insert to this layout.

Alexander.

[NicolasBBS]

Hello Alexander,

Thank you very much for your answer, you have solved my problem, and your sample code is exactly what I needed.
I didn't know that I had to delete manually the PaperSpaceBlock (actually I'm not a DXF/DWG specialist and I don't know what it is exactly...).
I will follow your suggestion : I'll put my code out of your component, without creating the DrawBlock procedure which is useless. And then I'll create the "block view" layout only once.

Best regards.