dev-cpp-users

[Dev-C++] Help Please. ( Scrolling the client area with graphics)

[santhosh s. p <psa...@re...>]

Hi ,=0A     I'm Santhosh an engineering student. Right now I'm doing a proj=
ect on graphics using devc++ 4.8 . I have a problem.=0AThe problem is that =
once I draw line or a text on the window and scroll the  vertical scroll ba=
rs the lines  that I had drawn would get erased.=0Akindly suggest me way so=
 that any graphics I put on the screen at runtime and then even after scrol=
ling the scroll bars the graphics thus scrolled should not get erased after=
 unscrolling later.=0A=0AEagerly waiting for your kind  and a positive resp=
onse.=0ASanthosh.=0A

Re: [Dev-C++] Help Please. ( Scrolling the client area with graphics)

[Per W. <pw...@ia...>]

This is how graphics works in most graphical environments, i.e. it is up
to the application to keep track of what is drawn and to repaint the
window on request.

Paint to a bitmap and redraw the bitmap suitably scrolled whenever the
window gets a repaint command. Or work with vector graphics, i.e. keep a
list of all draw commands needed to redraw the graphics and then walk
through the list and repaint all lines, circles, characters.

There are some libraries - or sample code - that performs the above
operations. Select a graphics library of your choice and check through the
example programs.

/Per W

On 22 Sep 2004, santhosh shenoy p wrote:

> Hi ,
>      I'm Santhosh an engineering student. Right now I'm doing a project on graphics using devc++ 4.8 . I have a problem.
> The problem is that once I draw line or a text on the window and scroll the  vertical scroll bars the lines  that I had drawn would get erased.
> kindly suggest me way so that any graphics I put on the screen at runtime and then even after scrolling the scroll bars the graphics thus scrolled should not get erased after unscrolling later.
>
> Eagerly waiting for your kind  and a positive response.
> Santhosh.
>

Re: [Dev-C++] Help Please. ( Scrolling the client area with graphics)

[<or...@vp...>]

Per Westermark wrote:

> This is how graphics works in most graphical environments, i.e. it is u=
p
> to the application to keep track of what is drawn and to repaint the
> window on request.
>=20
> Paint to a bitmap and redraw the bitmap suitably scrolled whenever the
> window gets a repaint command. Or work with vector graphics, i.e. keep =
a
> list of all draw commands needed to redraw the graphics and then walk
> through the list and repaint all lines, circles, characters.

Added to this:
Note that Windows can move the entire contents of a window, and you only =
need to repaint=20
the "invalid" rectangle (a small portion) of your window, giving you grea=
t speedups (and=20
to avoid flicker). Though you have to calculate that rectangle yourself. =
Process the=20
scrollbar messages, and retrieve the amount that was scrolled, then use t=
he=20
ScrollWindowEx() function to move the contents of your window (your lines=
, etc.), then=20
repaint the invalid rectangle (using BitBlt if you painted to a bitmap, o=
r any other=20
method). The invalid rectangle is what you scrolled into view.

The functions you should take a look at at the windows docs:
ScrollWindowEx()
BitBlt()
StretchBlt() // for zooming, maybe later
And of course "Bitmaps" in general.

The windows GDI functions will be more than sufficient for most drawings,=
 and I assume it=20
will be enough for you too (no need for additional libraries).

--
Greetings,
   Bal=E1zs

Re: [Dev-C++] Help Please. ( Scrolling the client area with graphics)

[<or...@vp...>]

OROSZI Bal=E1zs wrote:
> Added to this:
> Note that Windows can move the entire contents of a window, and you onl=
y=20
> need to repaint the "invalid" rectangle (a small portion) of your=20
> window, giving you great speedups (and to avoid flicker). Though you=20
> have to calculate that rectangle yourself. Process the scrollbar=20
> messages, and retrieve the amount that was scrolled, then use the=20
> ScrollWindowEx() function to move the contents of your window (your=20
> lines, etc.), then repaint the invalid rectangle (using BitBlt if you=20
> painted to a bitmap, or any other method). The invalid rectangle is wha=
t=20
> you scrolled into view.

A little correction:
After you got the amount to the scroll, call ScrollWindowEx() with the SW=
_INVALIDATE flag=20
then call UpdateWindow().
In your WM_PAINT message processor, use the PAINTSTRUCT's rcPaint rect, t=
hat holds the=20
invalid rect.

This way you don't need to calculate the rectangle yourself.

If you're stuck, look here for a complete example:
http://msdn.microsoft.com/library/default.asp?url=3D/library/en-us/shellc=
c/platform/commctls/scrollbars/usingscrollbars.asp

--
Greetings,
   Bal=E1zs