PCopy
Copies one graphical or text page onto another
Syntax
`
Declare Function PCopy ( ByVal source As Long = -1, ByVal destination As Long = -1 ) As Long
`
Usage
`
PCopy [ source ] [, destination ]
`
Parameters
`source`
page to copy from
`destination`
page to copy to
Return Value
Returns zero (`0`) if successful, or a non-zero error code to indicate a failure.
Description
Copies one graphical or text video page to another. Useful for drawing all graphics on one invisible page and copying it to the active visible page - creating smooth graphics and animation. Known as 'double buffering' or 'page flipping'.
`source` and `destination` refer to page numbers. The 'source' page is copied over the 'destination' page when pcopy is called.
If the `source` argument is omitted, the current working page is assumed. If the `destination` page is omitted, the current visible page is assumed.
`PCopy` is inactive if the `destination` page is locked.
The error code returned by `PCopy` can be checked using `Err` in the next line. The function version of `PCopy` returns directly the error code as a 32 bit `Long`.
Example
`
'Sets up the screen to be 320x200 in 8-bit color with 2 video pages.
ScreenRes 320, 200, 8, 2
'Sets the working page to 1 and the displayed page to 0
ScreenSet 1, 0
'Draws a circle moving across the top of the screen
For x As Integer = 50 To 269
Cls 'Clears the screen so we can start fresh
Circle (x, 50), 50, 14 'Draws a yellow circle with a 50 pixel radius on page 1
PCopy 1, 0 'Copies our image from page 1 to page 0
Sleep 25 'Waits for 25 milliseconds.
Next x
'Wait for a keypress before the screen closes
Sleep
`
`
'' Compile with -lang fblite or qb
#lang "fblite"
'' Console mode example:
'' Set the working page number to 0, and the visible page number to 1
#if __FB_LANG__ = "QB"
Screen ,, 0, 1
#else
Screen , 0, 1
#endif
Dim As Integer i, frames, fps
Dim As Double t
t = Timer
Do
'' Fill working page with a certain color and character
Cls
Locate 1, 1
Color (i And 15), 0
Print String$(80 * 25, Hex$(i, 1));
i += 1
'' Show frames per second
Color 15, 0
Locate 1, 1
Print "fps: " & fps,
If Int(t) <> Int(Timer) Then
t = Timer
fps = frames
frames = 0
End If
frames += 1
'' Copy working page to visible page
PCopy
'' Sleep 50ms per frame to free up cpu time
Sleep 50, 1
'' Run loop until the user presses a key
Loop Until Len(Inkey$)
`
Platform Differences

- Maximum number of text pages in Windows is 4.
- Maximum number of text pages in DOS is 8.
- Maximum number of text pages in all other targets is 1.
- Maximum number of graphics pages depends on what was specified when the `Screen` or `ScreenRes` statement was called.

Differences from QB

- None

See also

- `ScreenCopy`
- `Flip`
- `Screen`