paintTo() and Win 98 vs win Xp

[Kistal]

Hello, I am having a bit of a disturbing problem that is leaving me clueless...

I have written a component to display a set of "results", consisting of a name (TEdit), a score (TEdit), and a remark (TMemo). Each result is an instance of a self-written class called TEvaluationLine.

TEvaluationRoster is the wrapping class and actual component, containing methods to manipulate the TEvaluationLines it owns.

TEvaluationRoster has a method called "getPrintableVersion()" which returns a bitmap suited to assign to a Printer Canvas. This method basically asks all the TEvaluationRoster's TEvaluationLines to execute their asBitmap() method, which returns a small bitmap of that specific result, using the paintTo() method of the TEdits and the TMemo to create this bitmap. The TEvaluationRoster then assembles these small bitmaps into a large one and returns it.

Now the problem is that this approach works perfectly under winXp, but for some reason just produces a blank page using win98... Could someone tell me what I'm doing wrong here?

Relevant Code excerpts pasted below.

function TEvaluationLine.asBitmap : TBitMap;
var
smallbmp : TBitMap;
begin
smallBmp := TBitMap.Create;
smallBmp.Width:=TotalWidth;
smallBmp.Height:=Height;
smallbmp.Canvas.Lock;
fCaption.PaintTo(smallbmp.canvas.Handle,0,0);
fEvaluation.PaintTo(smallbmp.canvas.Handle,fCaption.Width,0);
fRemark.PaintTo(smallbmp.canvas.Handle,fCaption.Width+fEvaluation.Width,0);
smallbmp.Canvas.Unlock;
asBitmap:=smallBmp;
end;

function TEvaluationRoster.GetPrintableVersion(inWidth : Integer): TBitMap;
var
scale : double;
smallBmp, bigBmp : TBitMap;
index1,index2 : Integer;
topheight : Integer;
orgHeight:Integer;
begin
orgHeight:=self.Height;
self.ResizeToFitCellHeight;
index1:=0;
index2:=0;
topheight:=0;
bigBmp:=TBitMap.Create;
bigBmp.Width:=inWidth;
scale:=RosterWidth/inWidth;
bigbmp.Height:=Round(RosterHeight/scale);
for index1:=0 to fCols-1 do
begin
topheight:=0;
for index2:=0 to fRows-1 do
begin
smallBmp := fCells[index2,index1].asBitmap;
bigBmp.Canvas.StretchDraw(
Rect(Round(bigbmp.Width*index1/fCols),
topheight,
Round(bigbmp.Width*index1/fCols)+Round(bigBmp.Width/fCols),
topheight+Round(smallbmp.Height/(fCols*scale))
)
,smallBmp);
topheight:=topheight+Round(smallbmp.Height/(fCols*scale));
end;
end;
getPrintableVersion:=bigBmp;
self.Height:=orgHeight;
freeandnil(smallbmp);
end;

procedure TFParent.PrintDiscriminationReport(MyCanvas: TCanvas; Scale: Integer);
var i,x,y,y_start: word;
margin, LongestCol1, LongestCol2, LongestCol3: word;
myClientData: TClientMetaData;
bmp : TBitMap;
oldtab : Integer;
begin
myClientData := GetClientMetaData();
// exit if no clientmetadata!
if not myClientData.Complete then exit;
// Fill canvas:
oldtab:=self.Page.ActivePageIndex;
self.Page.ActivePageIndex:=2;
(...)
bmp:=self.DiscrimStrGrd.getPrintableVersion(printer.PageWidth-20);
mycanvas.Draw(10,y,bmp);
Freeandnil(bmp);
self.Page.ActivePageIndex:=oldtab;
end;

 

[Zathras]

I'm a little surprised it works at all. I don't use custom components, but normally a function that looks like this...

  function TEvaluationLine.asBitmap : TBitMap;
  var
    smallbmp : TBitMap;
  begin
    smallBmp := TBitMap.Create;
     :
     :
    asBitmap:=smallBmp;
  end;

... would be returning a pointer a memory location that is valid only while the function is executing. It probably works ok until the memory reserved for

 smallbmp

gets over-written, but the result would be unpredictable. If it works in XP I would guess that XP handles memory differently than 98.

 

[Kistal]

Hmmm that would explain things, lol... Did I mention I'm a Delphi noob?

So I guess I'll have to pass some bitmap as parameter rather than creating it in the function itself, huh? I can do that. *nods*

Can't try it out till monday, tho
*cries*
Me wanna code!

Oh, and thanks

 

[Kistal]

The problem seems to be more persistent than I thought.

Win98 still generates blank pages... Could someone check my new version of the code and tell me what else could be the cause, because I am so lost this time...


procedure TEvaluationLine.asBitmap(var smallBmp : TBitMap);
begin
smallBmp.Width:=TotalWidth;
smallBmp.Height:=Height;
smallbmp.Canvas.Lock;
fCaption.PaintTo(smallbmp.canvas.Handle,0,0);
fEvaluation.PaintTo(smallbmp.canvas.Handle,fCaption.Width,0);
fRemark.PaintTo(smallbmp.canvas.Handle,fCaption.Width+fEvaluation.Width,0);
smallbmp.Canvas.Unlock;
end;



procedure TEvaluationRoster.GetPrintableVersion(inWidth : Integer; var bigBmp : TBitMap);
var
scale : double;
smallBmp : TBitMap;
index1,index2 : Integer;
topheight : Integer;
orgHeight:Integer;
begin
smallBmp := TBitMap.Create;
orgHeight:=self.Height;
self.ResizeToFitCellHeight;
bigBmp.Width:=inWidth;
scale:=RosterWidth/inWidth;
bigbmp.Height:=Round(RosterHeight/scale);
for index1:=0 to fCols-1 do
begin
topheight:=0;
for index2:=0 to fRows-1 do
begin
fCells[index2,index1].asBitmap(smallBmp);
bigBmp.Canvas.StretchDraw(
Rect(Round(bigbmp.Width*index1/fCols),
topheight,
Round(bigbmp.Width*index1/fCols)+Round(bigBmp.Width/fCols),
topheight+Round(smallbmp.Height/(fCols*scale))
)
,smallBmp);
topheight:=topheight+Round(smallbmp.Height/(fCols*scale));
end;
end;
self.Height:=orgHeight;
freeandnil(smallbmp);
end;



procedure TFParent.PrintDiscriminationReport(MyCanvas: TCanvas; Scale: Integer);
var i,x,y,y_start: word;
margin, LongestCol1, LongestCol2, LongestCol3: word;
myClientData: TClientMetaData;
bmp : TBitMap;
oldtab : Integer;
begin
myClientData := GetClientMetaData();
// exit if no clientmetadata!
if not myClientData.Complete then exit;
// Fill canvas:
oldtab:=self.Page.ActivePageIndex;
self.Page.ActivePageIndex:=2;
(...)
bmp := TBitMap.Create;
self.DiscrimStrGrd.getPrintableVersion(printer.PageWidth-20, bmp);
mycanvas.Draw(10,y,bmp);
Freeandnil(bmp);
self.Page.ActivePageIndex:=oldtab;
end;

 

[sggaunt]

As a Newbie (presume thats what noob means) you seem to be jumping in at the deep end somewhat!
The only thing I can pickup is that I cant see where you are setting the parent of your new graphic object, though I dont know why this would make a difference under XP.

Dropping a lot of code on the forum can put some readers off, but not Zathras thats why he's top dog I suppose.

Steve

 

[Kistal]

Risking being branded as a whiner, I'm going to top this and hope someone comes along that can help me