Mega Code Archive
Setting the invisible color of a transparent image
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Title: Setting the invisible color of a transparent image
Question: How can I set the invisible color of a transparent image to other than the pixel in the lower-left corner?
Answer:
Transparent image
-----------------
The TImage component has a Transparent property that when set to True
displays the bitmap of the Picture property transparently. To do this,
it takes the color of the bottom-leftmost pixel and treates all pixels
of this color as invisible (you can see the objects begind the
TImage). For example, this bitmap...
GGGGGGGGG
GRRRRRRRG
GRRRRRRRG
GRRRRRRRG
GGGGGGGGG
...would be seen this way:
RRRRRRR
RRRRRRR
RRRRRRR
Since the pixel of the lower-left corner is green (G), all green
pixels are made invisible. But, what if we wanted to see the image
this way?
GGGGGGGGG
G G
G G
G G
GGGGGGGGG
TransparentColor and TransparentMode
------------------------------------
To achieve this result, we have to set the TransparentColor and
TransparentMode properties of the bitmap at run-time, for example
when the form is created:
procedure TForm1.FormCreate(Sender: TObject);
begin
with Image1.Picture.Bitmap do begin
TransparentColor := clMaroon;
TransparentMode := tmFixed;
end;
end;
TransparentColor is the color (Color) that will be considered
invisible. For example, we can use a constant (like $00800000,
clMaroon or clBtnFace) or we can get the color from some pixel of the
bitmap (like Canvas.Pixels[1,1]). TransparentMode is tmAuto by
default, meaning it takes the color of the pixel in the lower-left
corner, and we have to set it to tmFixed (the other possible value)
to tell the bitmap to use the color stored in the TransparentColor
property as the invisible color.
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