video memory segment

 BBS: Inland Empire Archive
Date: 05-19-92 (18:43)             Number: 137
From: CORIDON HENSHAW              Refer#: NONE
  To: JOHN GALLAS                   Recvd: NO  
Subj: video memory segment           Conf: (2) Quik_Bas

In a msg on <May 17 10:41>, John Gallas of 1:282/30 writes:

 JG> @EID:111a 01e99a45
 JG> @MSGID: 1:282/30 458acd8b
 JG> @PID: PB 1.21
 JG>    Is there a way that I can determine wether to use &HB000 or &HB800
 JG> when doing stuff with the screen?  And also, how do I save and load
 JG> screens with BSAVE and BLOAD?

That depends on the screen mode, anything OVER mode 2 is &Ha0000.  BUT if you
POKE, PEEK, BLOAD or BSAVE &Ha0000, you'll only get the
current bit-plain.  You need to OUT to select bit-plains.
here's some sample code to save and load screen 8-12
screens:


'Save a graphics screen
  DEFINT A - Z
  DEF SEG = &HA000            'Video segment
  FOR i = 0 TO NrBitPlanes - 1
      OUT &H3CE, 4            'Select the Read Map Select Register
      OUT &H3CF, i            'Select the bit plane to save
      BSAVE "PLANE" + CHR$(i + 48), 0, NrBytes
  NEXT i

'  The variables NrBitPlanes and NrBytes have the following values:
'
'  Screen     NrBitPlanes    NrBytes
'  ------     -----------    -------
'    7            4           8000
'    8            4          16000
'    9            4          28000
'   10            2          28000
'   11            4          38400
'   12            4          38400
'
'  You'll end up with 4 files (2 for SCREEN 10):
'
'      Filename       Contents
'      --------       --------
'       PLANE0        Blue bit plane
'       PLANE1        Green bit plane
'       PLANE2        Red bit plane
'       PLANE3        Intensity bit plane
'
'
'  Restoring these screens is a little different:
'
'Restore a graphics screen
  DEFINT A - Z
  DEF SEG = &HA000
  FOR i = 0 TO NrBitPlanes - 1
      OUT &H3C4, 2               'Select the Map Mask Register
      OUT &H3C5, 2 ^ i           'Select the bit plane to restore
      BLOAD "PLANE" + CHR$(i + 48), 0
  NEXT i

--- msgedsq 2.0.5
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