SelectBGPic(id[, mode, combomode])
id as the current output
device. This command be used in various different modes. The usual mode
to use SelectBGPic() is layers mode (#SELMODE_LAYERS) which is also the
default mode. Layers mode means that all graphics data that are
output by Hollywood will be added as layers to this background picture.
Therefore you will have to enable layers before using this command in
layers mode. Your background picture will never be modified in layers
mode, it will just get more and more layers.
Alternatively, you can use the #SELMODE_NORMAL or #SELMODE_COMBO modes.
These modes will modify your BGPic's data. They can only be used on
BGPics that are currently not associated with a display. #SELMODE_NORMAL
means that only the color channels of the BGPic will be altered when you
draw to it. The transparency channel of the BGPic (can be either a mask
or an alpha channel) will never be altered. You can change this behaviour
by using #SELMODE_COMBO in the optional mode argument. If you use this
mode, every Hollywood graphics command that is called after SelectBGPic()
will draw into the color and transparency channel of the BGPic. If the
BGPic does not have a transparency channel, #SELMODE_COMBO behaves the
same as #SELMODE_NORMAL.
Starting with Hollywood 5.0 you can use the optional combomode argument
to specify how #SELMODE_COMBO should behave. If combomode is set to
0, the color and transparency information of all pixels in the source
image are copied to the destination image in any case - even if the
pixels are invisible. This is the default behaviour. If combomode is set
to 1, only the visible pixels are copied to the destination image. This
means that if the alpha value of a pixel in the source image is 0, i.e. invisible,
it will not be copied to the destination image. Hollywood 6.0 introduces
the new combomode 2. If you pass 2 in combomode, Hollywood will blend
color channels and alpha channel of the source image into the destination
image's color and alpha channels. When you draw the destination image later,
it will look as if the two images had been drawn on top of each other
consecutively. Please note that the combomode argument is only supported
together with #SELMODE_COMBO. It doesn't have any effect when used with the
other modes.
Note that when you use #SELMODE_NORMAL or #SELMODE_COMBO, the original
graphics of the BGPic are modified. You will always be drawing to the
original graphics of the BGPic. Imagine that you have a 640x480 BGPic
that is currently scaled to 800x600 because you called ChangeDisplaySize().
If you call SelectBGPic() with #SELMODE_NORMAL or #SELMODE_COMBO now on
this BGPic, you will actually be drawing to the 640x480 picture. The
800x600 picture will be updated when EndSelect() is called. On EndSelect(),
Hollywood will scale the original graphics to the current output size
of the BGPic, but your initial drawing will always occur on the original
BGPic.
An alternative way to draw into the transparency channels of a BGPic is
to do this separately using SelectMask() or SelectAlphaChannel(). These
two commands, however, will write data to the transparency channel only.
They will not touch the color channel. So if you want both channels,
color and transparency, to be affected, you need to use SelectBGPic()
with mode set to #SELMODE_COMBO.
When you are finished with rendering to your BGPic and want your display to become the output device again, just call EndSelect().
Only commands that output graphics directly can be used after
SelectBGPic(). You may not call animated functions like MoveBrush() or
DisplayBrushFX() while SelectBGPic() is active.
When mode is set to #SELMODE_LAYERS, SelectBGPic() can also come handy
when you want to make multiple changes to the layers of the current BGPic
without causing a refresh after each change. For example, you may want to
insert 100 new layers at once. This would be pretty slow if you did
it in the conventional way because Hollywood would refresh the display a
hundred times. To avoid this, you can simply call SelectBGPic() and insert
the 100 layers and Hollywood will not refresh the display before you call
EndSelect(). Inside a SelectBGPic()-EndSelect() block, you can do as many
changes as you like. They will not be drawn before EndSelect() is called.
See below for an example.
#SELMODE_LAYERS, #SELMODE_NORMAL or #SELMODE_COMBO;
defaults to #SELMODE_LAYERS (V4.5)#SELMODE_COMBO is active (see above);
defaults to 0 (V5.0)EnableLayers() SelectBGPic(2) TextOut(#CENTER, #CENTER, "Hello World") Box(0, 0, 100, 100, #RED) Box(#RIGHT, #BOTTOM, 100, 100, #BLUE) EndSelect() DisplayBGPic(2)The above code selects background picture 2 as the current output device and adds three layers to it (one text and two rectangles). After that, the display is selected as the output device and then background picture 2 is displayed with its three layers.
SetFillStyle(#FILLCOLOR) EnableLayers SelectBGPic(1) ; we assume that 1 is our current BGPic ; add 100 random layers For Local k = 1 To 100 Box(Rnd(540), Rnd(380), 100, 100, RGB(Rnd(255), Rnd(255), Rnd(255))) Next EndSelect ; now the 100 layers are drawn in one go!This code illustrates the case discussed above. You need to make lots of changes and you want to defer drawing for performance reasons. In our case, we want to add 100 layers to the current BGPic. So we encapsulate this code by a
SelectBGPic()-EndSelect block. Hollywood will silently
add the 100 layers and will draw them in one go when EndSelect() is
called. This is much faster than adding them without SelectBGPic() because
in that case every call to Box() would cause a refresh.