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Archived:Drawing with monochrome masks may produce incorrect results on S60 3rd Edition FP2 (Known Issue)

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Drawing masked bitmaps using a monochrome (1 bit per pixel) bitmap as a mask may produce incorrect output on S60 3rd Edition, Feature Pack 2 devices.

Article Metadata
Tested with
Devices(s): Reported against Nokia N85, Nokia N96
Platform(s): S60 3rd Edition, Feature Pack 2
S60 3rd Edition FP2
Keywords: BitBltMasked, EGray2
Created: User:Technical writer 1 (11 Nov 2008)
Last edited: hamishwillee (21 Jun 2012)

How to reproduce

Create or load a bitmap (CFbsBitmap) with the same colour depth as the screen device (screen display mode, typically EColor16MU) and an accompanying monochrome bitmap (display mode EGray2) with the identical size.

Draw the bitmap using a masked blit as follows:

 void CMyContainerControl::Draw( const TRect& aRect ) const
CWindowGc& gc = SystemGc();
TRect rect( Rect() );
gc.BitBltMasked(rect.iTl, iBitmapEColor16MU, rect, iMaskEGray2, EFalse);

On some devices, such as the Nokia N85, the monochrome mask does not work correctly but displays vertical stripes instead.


This problem does not occur when using masks with the colour depth identical to the parent bitmap. However, this consumes significantly more RAM memory compared to using 1-bpp monochrome bitmaps.

However, inverting the monochrome mask seems to produce correct results:

   gc.BitBltMasked(rect.iTl, iBitmapEColor16MU, rect, iMaskEGray2, '''ETrue''');

As a workaround for monochrome bitmaps, each mask could be inverted and drawn with the 5th parameter of BitBltMasked() (aInvertMask) set to ETrue.

This page was last modified on 21 June 2012, at 06:02.
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