Cls([color])
If the output device is the display, the current background picture will be restored and all layers and sprites will be removed. The color argument is not used in this case.
If the output device is a brush, it will be cleared with the specified color.
If the output device is a background picture, i.e. SelectBGPic() with
mode set to #SELMODE_LAYERS is active, all layers of that picture will be
removed. The color argument is not used in this case.
If the output device is a mask, Cls() will clear the pixels using the
mode that was installed by SetMaskMode(). The color argument is
not used in this case.
If the output device is an alpha channel, Cls() will fill the pixels
with the intensity specified using SetAlphaIntensity(). The color
argument is not used in this case.
Note that when the current draw target is palette-based and the palette mode is set
to #PALETTEMODE_PEN, this function will clear the screen using the pen set via SetDrawPen()
instead of the color passed to the function.
#BLACK);
only required when used while SelectBrush() is active