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Transparency
Most of the time when you display a
bitmap, you'd like the have some part of it
appear transparent. How else are you going
to be able to see Jupiter when you fly your
Vegan starship over it? It would look like a
rectangle with a ship in it flying over
Jupiter without transparency effects. What
you need to do is set a certain colour to be
the transparent colour, thus removing the
unsightly black rectangle, and leaving only
the colourful ship behind. I tend to use
black, so that's what we'll do here.
Dim CKey As DDCOLORKEY
CKey.low = vbBlack
CKey.high = vbBlack
Sprite.SetColorKey DDCKEY_SRCBLT, CKey
"CKey" is defined as a DirectDraw
Color Key. The "CKey" contains a "low" value
and a "high" value. This enables us to
define a range of colours as transparent (if
we want). For our purposes a single colour
will do fine: Black. We set "CKey.low" and "CKey.high"
to vbBlack. All we have to do after that is
set the "Sprite.SetColorKey" method using
the color key we've created. Also the flag "DDCKEY_SRCBLT"
indicates that we want to apply this key to
the source bitmap when we blt it. This will
make more sense in a second:
BackBuffer.Blt DestRect, Sprite, SrcRect,
DDBLT_KEYSRC Or DDBLT_WAIT
Now when we blt the surface we
have to specify the "DDBLT_KEYSRC" flag to
ensure that the color key of the source (the
"Sprite" surface) is considered transparent
during the blt. That's all there is to it! |
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