Draw TBitmaps in DrawGrid in Delphi - delphi

Question

I have an 8 x 16 DrawGrid in Delphi XE5 that I would like to randomly fill with nine images I've stored in C:\Users\Sean Ewing\Documents\My Documents\Delphi Tutorials\Other\Math-O-Sphere\Win32\Debug\img. I'm currently trying to get one image to load to make sure I'm doing it correctly. Here is the code I've used to do this:
procedure TForm1.grdPlayFieldDrawCell(Sender: TObject; ACol, ARow: Integer;
Rect: TRect; State: TGridDrawState);
var
spherePlus: TBitmap;
begin
spherePlus.LoadFromFile(ExtractFilePath(Application.ExeName) + '\img\Sphere +1.bmp');
grdPlayField.Canvas.Draw(0, 0, spherePlus);
end;
The code compiles fine, and based on what I've read in the Embarcadero wiki this is correct, but I get an error at runtime when it's time to load the DrawGgrid. Where did I go wrong?

Answer 1

You need to first create the bitmap before you can use it:
procedure TForm1.grdPlayFieldDrawCell(Sender: TObject; ACol, ARow: Integer;
Rect: TRect; State: TGridDrawState);
var
spherePlus: TBitmap;
begin
spherePlus := TBitmap.Create;
try
spherePlus.LoadFromFile(ExtractFilePath(Application.ExeName) +
'\img\Sphere +1.bmp');
grdPlayField.Canvas.Draw(0, 0, spherePlus);
finally
spherePlus.Free;
end;
end;
The other thing you should be aware of is that the Rect parameter you receive in the event is the area that needs to be painted, so you'll want to use Canvas.StretchDraw and pass it that rectangle. It won't help with the current issue, but you'll need it when you move to the next step. You can identify the exact cell that's being drawn with the ACol and ARow parameters, so you can use that information to load a specific image for a column, for instance, or to output text for a column or row.
// Load specific image for the cell passed in ACol and ARow,
// and then draw it to the appropriate area using the Rect provided.
grdPlayField.Canvas.StretchDraw(Rect, spherePlus);