problem with transparency
lazarus / 39-Graphics

----------------------------------------------------------------------
Blue1987 · 2011-04-14 00:13

can anyone explain me what's wrong with this code??

Code: [Select]  image1.Canvas.Brush.Color:=clblue;
  image1.canvas.FillRect(0,0,image1.Width,image1.height);
  image2.Transparent:=true;
  {image2.Picture.Bitmap.TransparentColor:=clblack;
  image2.Canvas.Brush.Color:=clblack;
  image2.canvas.FillRect(0,0,image2.Width,image2.height);}
  image2.canvas.Pen.Color:=clred;
  image2.Canvas.Pen.Style:=pssolid;
  image2.Canvas.Line(0,image2.height,image2.width,0);

i simply would like image1 to stay in the background, and image2 to
show the red line only (and the rest transparent)...


thank you, Paolo

----------------------------------------------------------------------
Blue1987 · 2011-04-14 00:17

this is the output when I compile the code

(if I also use the code in the {}brackets it simply shows the blue
square)

----------------------------------------------------------------------
lainz · 2011-04-14 01:10

Quote from: Blue1987 on April 14, 2011, 02:13:52 amcan anyone explain
me what's wrong with this code??

...

i simply would like image1 to stay in the background, and image2 to
show the red line only (and the rest transparent)...


thank you, Paolo


Because you are drawing in Canvas, not assigning a Picture to TImage.
So you can't use Transparent property in this way.

This assign transparency in a temp bitmap, and then draw the bitmap in
the image2:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);var  bmp: TBitmap;begin 
image1.Canvas.Brush.Color:=clblue; 
image1.canvas.FillRect(0,0,image1.Width,image1.height);   bmp:=
TBitmap.Create;  bmp.Width:= image2.Width;  bmp.Height:=
image2.Height;   bmp.Transparent:=True; 
bmp.TransparentColor:=clBlack;   with bmp.canvas do begin 
Pen.Color:=clred;  Pen.Style:=pssolid; 
Line(0,image2.height,image2.width,0);  end;  
image2.Picture.Assign(bmp);  bmp.Free;end;

----------------------------------------------------------------------
Blue1987 · 2011-04-14 01:37

Quote from: lainz on April 14, 2011, 03:10:50 amQuote from: Blue1987
on April 14, 2011, 02:13:52 amcan anyone explain me what's wrong with
this code??

...

i simply would like image1 to stay in the background, and image2 to
show the red line only (and the rest transparent)...


thank you, Paolo


Because you are drawing in Canvas, not assigning a Picture to TImage.
So you can't use Transparent property in this way.

This assign transparency in a temp bitmap, and then draw the bitmap in
the image2:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);var  bmp: TBitmap;begin 
image1.Canvas.Brush.Color:=clblue; 
image1.canvas.FillRect(0,0,image1.Width,image1.height);   bmp:=
TBitmap.Create;  bmp.Width:= image2.Width;  bmp.Height:=
image2.Height;   bmp.Transparent:=True; 
bmp.TransparentColor:=clBlack;   with bmp.canvas do begin 
Pen.Color:=clred;  Pen.Style:=pssolid; 
Line(0,image2.height,image2.width,0);  end;  
image2.Picture.Assign(bmp);  bmp.Free;end;

thanks a lot!

----------------------------------------------------------------------
GBarton · 2013-03-26 20:57

I have tried the same code by Lainz but Image2 is black (not
transparent). Is there any way to make Image2 transparent? I am using
Lazarus 1.0.8.

----------------------------------------------------------------------
GBarton · 2013-04-03 22:50

Image2.Transparent:= true
and it works