Hi everyone,
I'm working on a graphics-related application. It will support things like
zooming and panning. As such, I would like to use double buffering to
reduce the screen flicker while panning. However, I'm having lots of
problems related to drawing to an offscreen window. Here's the general
idea:
1) Set the screen depth to the maximum supported by the device and save the
original depth
WinScreenMode ( winScreenModeGet, &width, &height, &depth, &enableColor);
mSavedDeviceScreenDepth = depth;
WinScreenMode ( winScreenModeGetSupportedDepths, &width,&height, &depth,
&enableColor);
.
. // calculate depth
.
WinScreenMode (winScreenModeSet, NULL,NULL, &depth, &enableColor);
2) Grab the bitmap from our database
3) Draw the bitmap on screen
WinDrawBitmap( bitmapP, rect->topLeft.x, rect->topLeft.y );
4) Create an offscreen window and draw the bitmap offscreen
if (!mOffscreenWindow)
mOffscreenWindow = WinCreateOffscreenWindow (mWindowBounds.extent.x,
mWindowBounds.extent.y, screenFormat, &err);
winH = WinSetDrawWindow (mOffscreenWindow);
WinDrawBitmap( bitmapP, 0, 0);
WinSetDrawWindow (winH);
5) Then while panning, copy the bitmap from offscreen on to the screen
WinSetClip(&mWindowBounds);
WinCopyRectangle (mOffscreenWindow, 0, &mWindowBounds, newX, newY,
winPaint);
WinResetClip();
6) On appStopEvent, restore screen depth to the orignal depth
if (mSavedDeviceScreenDepth) {
WinScreenMode ( winScreenModeGet, NULL,NULL, NULL, &enableColor);
WinScreenMode ( winScreenModeSet, NULL,NULL,
&mSavedDeviceScreenDepth,
&enableColor);
mSavedDeviceScreenDepth = mDeviceScreenDepth = 0;
}
Depending on what ROM I am running on, copying the pixels from offscreen to
screen gets fouled up. The pixels look as if they're inverted somehow.
Also when restoring the saved screen depth upon exiting, I usually get an
error that I have written to unallocated memory, causing a fatal exception
on a real device. However, if I do NOT draw offscreen, I don't have any
problems when restoring the saved screen depth. I tried running on
different ROMS, and here is what I have found:
ROM Version Copying offscreen->screen Restoring
screen depth
----------------------------------------------------------------------------
-------
35-ezdbg displays incorrectly error
35-colordbg displays incorrectly no
error
40-fulldbg "Bad Window" error when drawing to screen n/a
40-VZcolordbg displays correctly no error
I'm not sure if the problem is related to drawing offscreen, or copying from
offscreen to screen. But I do know that the images always look correct when
they are drawn to the screen. Any ideas?
Thanks a lot!
Nick Guarracino
[EMAIL PROTECTED]
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