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  1. #1
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    Is symbian can display the bitmaps with alpha channel?

    I can't display the bitmaps with alpha channel. I have tried to use bitmaps, but it seems bmp file don't support the alpha channel.
    I have tried the 32 png files, but after ImageConvertor, the png file is converted to 24 bit.
    If there any good solutions to get alpha channel bitmaps in symbian?

  2. #2
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    Re: Is symbian can display the bitmaps with alpha channel?

    anybody knows? Please help~~~

  3. #3
    Nokia Developer Moderator
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    Re: Is symbian can display the bitmaps with alpha channel?

    I have not actually checked what it does, but CImageDecoder::Convert(TRequestStatus* aRequestStatus, CFbsBitmap& aDestination, CFbsBitmap& aDestinationMask, TInt aFrameNumber=0) is said to extract a mask; it might be your alpha channel.

  4. #4
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    Re: Is symbian can display the bitmaps with alpha channel?

    This mask is only for the place which you want to make it transparent I think, but also thank you.
    Symbian game and application developer.
    Fat
    Good Luck

  5. #5
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    Re: Is symbian can display the bitmaps with alpha channel?

    "only"? Is not that what you require? (Note that BitBltMasked supports alpha blending - starting form Symbian 7.0 - if aMaskBitmap is of display mode EGray256, thus there is a chance that the decoded mask will also be a 8-bit one)

  6. #6
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    Re: Is symbian can display the bitmaps with alpha channel?

    Thanks for wizard_hu_'s answer, I have check the SDK and find these, it seems it didn't support alpha but only the transparent.

    Masks can be used to select which parts of a bitmap are drawn by the BitBltMasked function of the Windows Server. If a pixel in the mask is black, then the corresponding pixel is copied from the bitmap; if a pixel in the mask is white, then the corresponding pixel is not copied from the bitmap, which has the effect of displaying the background at that pixel location. This example uses a mask to draw circles to the screen. Without a mask, the circles would appear in a white square that moved around the screen as the image was animated. Note that mask is not copied to the screen, but is simply used to decide which pixels should get copied to the screen. Therefore, in order to reduce memory requirements, masks should have a colour depth of just 2 bits, rather than a colour depth of 12 bits.

    But I have found TGopBitBltAlphaBitmap. This can support the alpha blending but it seems should give two bitmaps for construction, one is the original bitmaps and the other is the alpha bitmaps, I don't know how to make the alpha bitmaps... Anyone knows?
    Symbian game and application developer.
    Fat
    Good Luck

  7. #7
    Nokia Developer Moderator
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    Re: Is symbian can display the bitmaps with alpha channel?

    Quote Originally Posted by SDK Help
    BitBltMasked
    ...
    This function uses either a black and white (binary) mask bitmap, or if aMaskBitmap's display mode is EGray256, alpha blending is used. Use of any other mode may result in unpredictable results. With aInvertMask=ETrue, black pixels in the mask bitmap stop corresponding pixels in the source bitmap from being transferred to the destination rectangle. With aInvertMask=EFalse, white pixels in the mask bitmap stop corresponding pixels in the source bitmap from being transferred to the destination rectangle.
    Check in documentation of CBitmapContext. Also note that although the documentation for CFbsBitGc and CWindowGc mentions only the binary transparency, alpha blending worked for CFbsBitGc when I have tried.

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