Decorating TImageCollection images with code - delphi

Question

For testing purposes, in my Delphi 10.3 application, I'd like to decorate images in a TImageCollection with the dimensions of each image. For bitmaps, it's no problem but for PNG files, I can't paint to that canvas, neither can I assign from a BMP to a PNG in TWICImage because of a runtime exception "cannot assign a TPngImage to a TWICImage".
procedure DecorateImageCollection(imcMainMisc: TImageCollection);
var
i, j: Integer;
bmp:Graphics.TBitmap;
item:TImageCollectionItem;
img:TImageCollectionSourceItem;
begin
for i := 0 to imcMainMisc.Count - 1 do
begin
item:=imcMainMisc.Images.Items[i];
for j := 0 to item.SourceImages.Count - 1 do
begin
img:=item.SourceImages.Items[j];
case img.Image.ImageFormat of
wifBmp:
;
wifPng:
begin
bmp:=Graphics.TBitmap.Create;
try
bmp.Assign(img.Image);
bmp.Canvas.Font.Name:='Small Fonts';
bmp.Canvas.Font.Size:=6;
bmp.Canvas.Font.Color:=clRed;
bmp.Canvas.Brush.Style:=bsClear;
bmp.Canvas.Pen.Style:=psSolid;
bmp.Canvas.TextOut(0, 0, IntToStr(bmp.Height));
// *cannot assign a TPngImage to a TWICImage*
img.Image.Assign(bmp);
finally
bmp.Free;
end;
end;
wifJpeg:
;
wifGif:
;
wifTiff:
;
wifWMPhoto:
;
wifOther:
;
end;
end;
end;
end;
I expect such an operation should be simple but I haven't yet found out how.
Thank you!

Answer 1

The solution I ended up using was deleting the PNG source item, adding a new source item and using LoadFromStream( ).
procedure DecorateImageCollection(imc: TImageCollection);
var
i, j, x, y: Integer;
r:TRect;
rSize:TSize;
sTag:string;
bmp:TBitmap;
png:TPngImage;
item:TImageCollectionItem;
str:TMemoryStream;
img, icsiNew:TImageCollectionSourceItem;
Alpha: PByte;
begin
for i := 0 to imc.Count - 1 do
begin
item:=imc.Images.Items[i];
for j := item.SourceImages.Count - 1 downto 0 do
begin
img:=item.SourceImages.Items[j];
case img.Image.ImageFormat of
wifBmp:
begin
bmp:=TBitmap.Create;
try
bmp.Assign(img.Image);
sTag:=IntToStr(bmp.Height);
bmp.Canvas.Font.Name:='Small Fonts';
bmp.Canvas.Font.Size:=6;
rSize:=bmp.Canvas.TextExtent(sTag);
r.Top:=0;
r.Left:=0;
r.Width:=rSize.Width;
r.Height:=rSize.Height;
bmp.Canvas.Brush.Color:=clWhite;
bmp.Canvas.Brush.Style:=bsSolid;
bmp.Canvas.Font.Color:=clRed;
bmp.Canvas.Pen.Style:=psSolid;
bmp.Canvas.TextOut(r.Left, r.Top, sTag);
img.Image.Assign(bmp);
finally
bmp.Free;
end;
end;
wifPng:
begin
png:=TPngImage.Create;
str:=TMemoryStream.Create;
try
img.Image.SaveToStream(str);
str.Position:=0;
png.LoadFromStream(str);
sTag:=IntToStr(png.Height);
png.Canvas.Font.Name:='Small Fonts';
png.Canvas.Font.Size:=6;
rSize:=png.Canvas.TextExtent(sTag);
r.Top:=0;
r.Left:=0;
r.Width:=rSize.Width;
r.Height:=rSize.Height;
// knock out transparency in that area
for Y := r.Top to r.Bottom - 1 do
for X := r.Left to r.Right - 1 do
begin
Alpha := #png.AlphaScanline[Y]^[X];
Alpha^ := 255; // opaque
end;
png.Canvas.Brush.Color:=clWhite;
png.Canvas.Brush.Style:=bsSolid;
png.Canvas.Font.Color:=clRed;
png.Canvas.Pen.Style:=psSolid;
png.Canvas.TextOut(r.Left, r.Top, sTag);
str.Clear;
png.SaveToStream(str);
item.SourceImages.Delete(j);
icsiNew:=item.SourceImages.Add;
str.Position:=0;
icsiNew.Image.LoadFromStream(str);
finally
png.Free;
str.Free;
end;
end;
wifJpeg:
;
wifGif:
;
wifTiff:
;
wifWMPhoto:
;
wifOther:
;
end;
end;
end;
end;