Double buffers are extremely useful if many graphics have to be drawn in a screen update. If you only need to move a little player image around, you should better use sprites because that is faster. Remember that a double buffered display will always refresh the whole screen. Thus, if you have an application running in 640x480 at 25fps, it will be quite some work for Hollywood because it has to draw a screen of 640x480 25 times a second.
Double buffers are installed on a per display basis. Thus, when you call
BeginDoubleBuffer(), it will change the currently selected display into
a double-buffered one. It will not change all displays to double-buffered!
If you want all your displays to be double-buffered, you need to call
BeginDoubleBuffer() for each of your displays.
Some restrictions apply:
BeginDoubleBuffer()is called must not be transparent.
Starting with Hollywood 5.0, there is a new optional argument
hardware that allows
you to enable hardware double buffering. On supported systems, this is much
faster than software double buffering because it will completely operate
in video memory which can use the GPU for drawing. There are some restrictions,
though: If you use a hardware double buffer, you should draw to it using
hardware brushes whenever this is possible. All other drawing commands will
be much slower! Only by using hardware brushes can you get full hardware
accelerated drawing. Using normal drawing functions with a hardware double
buffer can even be slower than using them on a software double buffer. This
is especially the case with graphics that use an alpha channel, e.g. anti-aliased
text or vector shapes, because for alpha channel drawing, Hollywood has to
read from the destination device which will be very slow for hardware double
buffers because reading from video memory is very slow. Thus, you should try
to use hardware brushes whereever possible when you work with a hardware
double buffer. See hardware brushes for details.
Please note that currently hardware double buffering is only supported on AmigaOS and Android by default. However, plugins that install a display adapter are also able to support hardware double buffers for their display adapter. In that case you can also use hardware double buffers on systems other than AmigaOS and Android. For example, the GL Galore and RebelSDL plugins allow you to use hardware double buffers on Windows, macOS, and Linux. See Obtaining plugins for details.
Please note that Hollywood might also fall back to single buffering on some systems. Therefore, it is not safe to assume that calling Flip() will really switch buffers. It could also just draw the single buffer and then simply let you draw on it again.
Falsewhich means software double buffering) (V5.0)
BeginDoubleBuffer() CreateBrush(1, 64, 64, #RED) For k = -64 To 640 Cls DisplayBrush(1, k, #CENTER) Flip Next EndDoubleBuffer()The code above moves a red rectangle from the outer left to the outer right without any visible flickering. This is not a good example because we only move a little image around. It is a lot of overhead to refresh the whole 640x480 pixels just for this little image, so you should better use sprites in this case. Remember that double buffering is only recommended when there are a lot of graphics to draw.