What you appear to be saying is that a TImage is MEANT to have
a pic in it and that when I do not do this I run into problems. I do
not like work-arounds so I can use things in non-standard ways. I
feel that it is better to use things (components in this case) in the
correct way.
I like the ideas in your last example. It appears as though this is
the "right" way to achieve what I want to achieve. I will have a play
with it tomorrow (after I get up today actually) and see if it does what
I want but I suspect that it is the way to go.
Thanks for you time.
Chrissy.
BTW - based on the name of this mailing list it is possible that it is
a good idea to write OP code - but hey, whatever works for you.
From: Corey Murtagh wrote
> Chrissy R wrote
> <snip>
> >> Something like:
> >
> >You may be correct - BUT - I don't understand that code. What is
> >fastcall? What is the "::"? What is "*" before "Sender"? What is
> >"->". This does not look like the Delphi code I write.
>
> Sorry, it was Borland C++ Builder code. I just copied it from an old
> project of mine. I've just had it pointed out to me that I should
> really present code examples in Delphi OP, so here goes:
>
> procedure TViewForm.ViewPanelResize(Sender: TObject);
> begin
> framebuffer.Width := Image1.Width;
> framebuffer.Height := Image1.Height;
> Image1.Picture.Assign(framebuffer);
> end;
>
> >> This forces the bitmap that the TImage's picture is stored in to be
> >> properly resized when the form size changes, which should fix the
> >> problem with not being able to draw to the whole image.
> >
> >That makes sense. It appears that a TImage needs an image to be
> >in it.
>
> When the TImage is created the TImage.Picture member is correctly
> initialised with a TPicture of the correct dimensions to store the
> actual image information in. Unfortunately when you resize the TImage
> it doesn't automatically resize the TPicture, so if you make the TImage
> larger you get blank bits where the Picture isn't big enough. By
> assigning a larger TBitmap to the Picture you force it to the correct
> dimensions.
>
> >> Can't say I've tried to use a TImage that size. However a
> >> 2048x2048x24 image is going to take up something like 12meg of ram,
> >> which is a little expensive. If you really need to support images
> >> this size I'd suggest trying something a little less memory hungry,
> >> even if it means a relatively large amount of time spent drawing.
> >
> >I cannot have it slow to draw. I need fast redrawing and efficient
> >programming. Students will be working on this code so it has to be
> >simple and not at all convoluted AND it has to be fast and flicker free
> >in the drawing.
>
> If you draw to a TBitmap and then copy it to the TImage using Image.
> Canvas.CopyRect(), then there is no flicker that I can detect. The
> image isn't cleared before the bitmap is copied. As for the memory...
> if you set the TBitmap.PixelFormat to pf8bit you'll get a 256-color
> bitmap which will be 1/3rd as large as an equivalent 24-bit bitmap.
> It's also faster to draw to than 24bit, although very slightly slower
> when copying to the screen.
>
> If redrawing every time the scrollbars move is too slow, how about
> using the same method but maintaining a complete copy of the image in a
> TBitmap? Then you select the appropriate section to copy into the
> smaller TImage. Let me see if I can express this in OP:
>
> procedure TViewForm.UpdateImage;
> var
> sRect, dRect: TRect;
> x, y: Integer;
> begin
> x = HScrollBar.Position;
> y = VScrollBar.Position;
> dRect := Image1.Canvas.ClipRect;
> sRect := dRect;
> Inc(sRect.Left,x);
> Inc(sRect.Right,x);
> Inc(sRect.Top,y);
> Inc(sRect.Bottom,y);
>
> Image1.Canvas.CopyRect(dRect, backbuffer.Canvas, sRect);
> end;
>
> Did that make any sense? I'm not really comfortable writing OP :>
>
> Basically what I'm trying to achieve is to copy a rectangle the same
> size as the TImage from a selected position in a larger TBitmap.
>
>
> >Is there a component that is a line? I want a line that can go on any
> >angle and that I can select and pickup and move.
>
> Not a standard one, although there may be a third-party one floating
> around somewhere.
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