why does png lose transparency on triple buffer or stretch?
lazarus / 39-Graphics

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jw · 2010-03-21 18:36

ok If I make 2 sprite buffers like so

spritenormal : TCustomBitmap;
spritestretched : TCustomBitmap;

spritenormal:= TPortableNetworkGraphic.Create;
spritestretched:= TPortableNetworkGraphic.Create;

and load sprite normal form a timagelist like so
spriteimages.GetBitmap(0, spritenormal);

then do a stretch to fit multiple screen resolution
spritestretched.Canvas.StretchDraw(rect(0,0,screen.width*0.50,screen.h
eight*0.50),spritenormal);

then draw it to the form canvas like so
Canvas.Draw(0,0, spritestretched);

I lose the transparency of the ping in the stretchdraw command,
but of I decide to just display the loaded spritenormal it works fine?
how do I fix this??????

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Marc · 2010-03-21 21:44

Drawing alpha is limited supported. When loading from images, a canvas
has alpha, but as soon as you draw on it, the (destination) canvas
looses alpha.
Just think of it, how do you want to make a difference in drawing in
the following examples:
1) draw an alpha image on an exiting background, so the image blends
2) draw an alpha image on an exiting background, so the image replaces

At this moment, the LCL only does 1.

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jw · 2010-03-21 23:26

is there a hex value I can put into $????????; that will paint the
canvas background transparent with a draw command?

Canvas.pen.Color := $????????;
Canvas.brush.Color := $????????;
Canvas.rectangle(0,0,width,Height);

if no!!!!
Then is there a way to stretch without doing the stretchdaw?
lf I'm pulling an image from a timiagelist can it be stretched within
the timagelist during runtime before it's loaded into the
tcustombitmap?

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circular · 2010-03-21 23:40

With my lib ( http://consume.o2switch.net/lazarus/bgrabitmap.zip ) you
can do it this way :
Code: [Select]var OriginalBitmap, StretchedBitmap: TBGRABitmap;
begin
  OriginalBitmap := TBGRABitmap.Create('some_image.png');
  StretchedImage := TBGRABitmap(OriginalBitmap.Resample(200,200));
  StretchedImage.Draw(Canvas,0,0,False);
end;

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jw · 2010-03-23 14:57

wow circular you're far beyond my codeing skills.  I'll check out the
library but for now I still want to deal with the LCL and learn it.
 My thinking is that the LCL will do what I want because you can do an
image stretch within a timagelist without loseing transparency.  I
just can't find the command to to it.


example I have a transparent image in a tcustombitmap and don't use
any draw commands on it then I should be able to make another timage
list for the stretching. 

Modifing the original post

ok If I make a sprite buffer like so

sprite : TCustomBitmap;

sprite:= TPortableNetworkGraphic.Create;


and load the unstretched sprite from a timagelist like so
spriteimages.GetBitmap(0, spritenormal);

then do a stretch to fit multiple screen resolution using a
timagelistbuffer

timagelistbuffer.width:=screen.width*0.50
timagelistbuffer.height:=screen.height*0.50;


how do you get  stretch from runtime with a timagelist??

timangelistbuffer.stretch:=true;         //this errors
timangelistbuffer.Insert(0, sprite, stretch);  //this errors
timangelistbuffer.Insert(0, sprite, nil); //this loads but no stretch

pull the stretched image back into the sprite

timagelistbufferbuffer.GetBitmap(0, sprite);



then draw it to the form canvas like so
Canvas.Draw(0,0, sprite);

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jw · 2010-03-23 20:52

the command that worked was

timagelist.insertmasked(index,tcustombitmap,mask color);

now I can stretch all my sprites then reclaim transpareny through an
imagelist and a backgroud color mask.

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circular · 2010-03-24 20:04

In fact you can directly draw an image from the TImageList with the
Draw method, but I guess the transparency is only 1-bit. I mean that
there can be opaque pixels or transparent pixels but nothing between
the two.

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jw · 2010-04-13 19:59

circular

how are you pulling the image directly from a timamgelist with a draw
command?


I first have to put the image into a tcutombitmap buffer then
stretchdraw it to another tcustombitmap.

It would be nice to skip a step.

this is the only command I know of to get the image out
timagelist.getbitmap(1,tcustombitmapbuffer)

then stretch it

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circular · 2010-04-14 09:25

As I said you can use the Draw method. For stretching, there is also a
StretchDraw method :
Code: [Select]  ImageList1.Draw(Canvas,x,y,index);
  ImageList1.StretchDraw(Canvas,index,rect(0,20,100,120));