Tuesday, 5 July 2011

Delphi 2010 Control Flickering

I have been upgrading or migrating our software from XP OS to be able to compile and run under Windows 7. Our software is starting to show issues that we didn't notice under Windows XP. Currently, I am dealing with a user defined control flickering on a TForm. It seems to flicker every now and then not always, but when it flickers it is very noticeable. I have set DoubleBuffered for the TForm and TTrendChart Class, but it is not helping.

This a user-defined control of TCustomPanel. It is supposed to display a Live Trendchart on a TForm.

TTrendChart = class(TCustomPanel)
private
  fCount
:integer;
  fColors
:array[0..7] of TColor;
  fNames
:array[0..7] of string;
  fMinText
:string16;
  fMaxText
:string16;
  fShowNames
:Boolean;
  fMaxTextWidth
:integer;
  data
:TList;
 
Indexer:integer;
  chartRect
:TRect;
  fWidth
:integer;
  fHeight
:integer;
  firstTime
:Boolean;
 
function GetColors(Index:integer):TColor;
  procedure
SetColors(Index:integer; const value :TColor);
 
function GetNames(Index:integer):string;
  procedure
SetNames(Index:integer; const value: string);
  procedure
SetCount(const value : integer);
  procedure rShowNames
(const value : Boolean);
  procedure
SetMaxText(const value:string16);
  procedure
SetMinText(const value:string16);
  procedure
RecalcChartRect;
protected
  procedure
Resize; override;
  procedure
Paint; override;
public
  constructor
Create(AOwner : TComponent); override;
  destructor
Destroy; override;
  procedure
PlotPoints(p1,p2,p3,p4,p5,p6,p7,p8:real);
  procedure
ClearChart;
  procedure
Print;
  property
TrendColors[Index:integer]: TColor read GetColors write SetColors;
  property
TrendNames[index:integer]: string read GetNames write SetNames;
published
  property
TrendCount: Integer read fCount write SetCount default 8;
  property
ShowNames: Boolean read fShowNames write rShowNames default true;
  property
MaxText:string16 read fMaxText write SetMaxText;
  property
MinText:string16 read fMinText write SetMinText;
  property
Align;
  property
Alignment;
  property
BevelInner;
  property
BevelOuter;
  property
BevelWidth;
  property
DragCursor;
  property
DragMode;
  property
Enabled;
  property
Caption;
  property
Color;
  property
Ctl3D;
  property
Font;
  property
Locked;
  property
ParentColor;
  property
ParentCtl3D;
  property
ParentFont;
  property
ParentShowHint;
  property
PopupMenu;
  property
ShowHint;
  property
TabOrder;
  property
TabStop;
  property
Visible;

  property
OnClick;
  property
OnDblClick;
  property
OnDragDrop;
  property
OnDragOver;
  property
OnEndDrag;
  property
OnEnter;
  property
OnExit;
  property
OnMouseDown;
  property
OnMouseUp;
  property
OnMouseMove;
  property
OnResize;
end;
 
 
Here how it created:
    constructor TTrendChart.Create(AOwner:TComponent);
var
  i
:integer;
  tp
:TTrendPoints;
begin
  inherited
Create(AOwner);
 
Parent := TWinControl(AOwner);
  fCount
:= 8;
  fShowNames
:= true;
 
Caption := '';
  fMaxText
:= '100';
  fMinText
:= '0';
  fMaxTextWidth
:= Canvas.TextWidth('Bar 0');
  firstTime
:= true;
 
BevelInner := bvLowered;
  data
:= TList.Create;
 
Indexer := 0;
 
RecalcChartRect;
 
DoubleBuffered:=true;
 
for i := 0 to 10 do
 
begin
    tp
:= TTrendPoints.Create(0.0 + 0.1 * fWidth,0.0,0.0,0.0,0.0,0.0,0.0,0.0);
    data
.Add(tp);
 
end;
 
for i := 0 to 7 do
 
begin
   
case i of
   
0: fColors[i] := clMaroon;
   
1: fColors[i] := clGreen;
   
2: fColors[i] := clOlive;
   
3: fColors[i] := clNavy;
   
4: fColors[i] := clPurple;
   
5: fColors[i] := clFuchsia;
   
6: fColors[i] := clLime;
   
7: fColors[i] := clBlue;
   
end;
    fNames
[i] := Format('Line %d',[i]);
 
end;
end;
Here is how it is painted on the Form:
    procedure TTrendChart.Paint;
var
  oldColor
:TColor;
  dataPt
:TTrendPoints;
  i
,j:integer;
  curx
:integer;
  count
,step:integer;
  r
:TRect;
begin
   inherited
Paint;

  oldcolor
:= Canvas.Pen.Color;

 
Canvas.Brush.Color:=clWhite;
  r
.Left:=chartRect.Left-25;
  r
.Right:=chartRect.Right+11;
  r
.Top:=chartRect.Top-11;
  r
.Bottom:=chartRect.Bottom+22;
 
Canvas.FillRect(r);

 
if FirstTime then
 
begin
    count
:= Indexer - 1;
 
end
 
else
    count
:= data.Count - 2;

   
{ Draw minute lines }
   
Canvas.Pen.Color := clBtnShadow;
    i
:= chartRect.left + 60;
   
while i < chartRect.Right do
   
begin
         
Canvas.Moveto(i, chartRect.top);
         
Canvas.LineTo(i, chartRect.bottom);
         i
:= i + 60;
   
end;

   
{ Draw value lines }

    step
:= (chartRect.bottom - chartRect.top) div 5;

   
if step > 0 then
   
begin
         i
:= chartRect.bottom - step;
         
while i > (chartRect.top + step - 1) do
         
begin
             
Canvas.Moveto(chartRect.left,i);
             
Canvas.LineTo(chartRect.right,i);
              i
:= i - step;
         
end;
   
end;

 
{ Draw Pens }
 
for j := 0 to fCount - 1 do
 
begin
   
Canvas.Pen.Color := fColors[j];
    dataPt
:= TTrendPoints(data.Items[0]);
   
Canvas.MoveTo(chartRect.left,PinValue(round(chartRect.bottom - (fHeight * dataPt.pnts[j] / 100.0)),
                                                                 chartRect
.top,chartRect.bottom));

   
for i := 1 to count do
   
begin
      dataPt
:= TTrendPoints(data.Items[i]);
     
if i <> Indexer then
     
begin
           
Canvas.LineTo(chartRect.left+i,PinValue(round(chartRect.bottom - (fHeight * dataPt.pnts[j] / 100.0)),
                                                               chartRect
.top,chartRect.bottom));
     
end
     
else
     
begin
           
Canvas.MoveTo(chartRect.left+i,PinValue(round(chartRect.bottom - (fHeight * dataPt.pnts[j] / 100.0)),
                                                                 chartRect
.top,chartRect.bottom));
     
end;
   
end;
 
end;

    r
:= chartRect;
   
InflateRect(r,1,1);
   
Canvas.Pen.Color := clBtnShadow;
   
Canvas.moveto(r.left,r.top);
   
Canvas.lineto(r.right,r.top);
   
Canvas.lineto(r.right,r.bottom);
   
Canvas.lineto(r.left,r.bottom);
   
Canvas.lineto(r.left,r.top);

   
{ draw index line }
//    Canvas.Pen.Color := clWhite;
   
Canvas.Pen.Color := clBlack;  
   
Canvas.MoveTo(chartRect.Left + Indexer,chartRect.top);
   
Canvas.LineTo(chartRect.left + Indexer, chartRect.bottom+1);
   
Canvas.Pen.Color := oldcolor;

   
Canvas.Font.COlor := clBlack;
   
Canvas.TextOut(chartRect.left-Canvas.TextWidth(string(fMinText))-2,chartRect.Bottom-8,string(fMinText));
   
Canvas.TextOut(chartRect.left-Canvas.TextWIdth(string(fMaxText))-2,chartRect.top-8,string(fMaxText));

   
if fShowNames then
   
begin
      curx
:= 32;
     
for i := 0 to fCount - 1 do
     
begin
       
Canvas.Font.Color := fColors[i];
       
Canvas.TextOut(curx,chartRect.bottom+4,fNames[i]);
        curx
:= curx +  fMaxTextWidth + 16;
     
end;
   
end;
end;
Here is how one would use it:
  TrendChart := TTrendChart.Create(form);
 

Any help will be appreciated. Thank you.


Answer:

ControlStyle := ControlStyle + [csOpaque];
 

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