**
**	$Id: GetViewModes.S,v 21.2 92/05/18 02:18:15 chris Exp $
**	$Revision: 21.2 $
**
**	$Filename: GetViewModes.S $
**	$Author: chris $
**	$Date: 92/05/18 02:18:15 $
**
**	iff.library/IFFL_GetViewModes
**
**	COPYRIGHT (C) 1987-1992 BY CHRISTIAN A. WEBER, BRUGGERWEG 2,
**	CH-8037 ZUERICH, SWITZERLAND.  ALL RIGHTS RESERVED.  NO PART
**	OF THIS SOFTWARE MAY BE COPIED, REPRODUCED,  OR  TRANSMITTED
**	IN ANY FORM OR BY ANY MEANS,  WITHOUT THE PRIOR WRITTEN PER-
**	MISSION OF THE AUTHOR. USE AT YOUR OWN RISK.
**


		IDNT	IFFL_GetViewModes
		SECTION	text,CODE

		INCLUDE	"graphics/view.i"
		INCLUDE	"IffLib.i"

		XREF	FindChunkFunc,GetBMHDFunc
		XDEF	CalcViewModes			; für SaveClip.S
		XDEF	GetViewModesFunc


******* iff.library/IFFL_GetViewModes ***************************************
*
*    NAME
*	IFFL_GetViewModes() -- Get Amiga-specific ViewModes
*
*    SYNOPSIS
*	viewmodes = IFFL_GetViewModes( iff )
*	D0                             A1
*
*	ULONG IFFL_GetViewModes( IFFL_HANDLE )
*
*    FUNCTION
*	Searches the IFF file for a 'CAMG' chunk which holds the view modes
*	information. If there is no CAMG chunk, the view modes are calcu-
*	lated using the information in the BitMapHeader structure.
*	You can directly put the low WORD of the result of a call to
*	IFFL_ GetViewModes() into the ns_ViewModes field of a NewScreen
*	structure, or you can use the whole ULONG for the SA_DisplayID tag
*	under OS 2.x.
*
*    INPUTS
*	iff - IFF file handle, from OpenIFF()
*
*    RESULT
*	viewmodes - ULONG containing the view modes (HAM, LACE, HIRES ...)
*	All forbidden bits are masked out, as suggested by CBM.
*	Under Kickstart V1.3, only the lower WORD is used.
*
*    BUGS
*	If the IFF file has no CAMG chunk and 6 bitplanes, the HAM bit
*	will be set. This is not always correct since the picture could
*	be in the Extra Halfbrite mode. You can load such Halfbrite
*	pictures into DPaint III and save them again, DPaint will generate
*	the correct CAMG chunk.
*
*    SEE ALSO
*	<graphics/displayinfo.h>
*
*****************************************************************************


MODESMASK	EQU	~(V_SPRITES|V_VP_HIDE|GENLOCK_AUDIO|GENLOCK_VIDEO)

GetViewModesFunc:
		move.l	a2,-(SP)

		movea.l	a1,a2			; A2 :  IFFFile
		move.l	#'CAMG',d0
		bsr	FindChunkFunc		; setzt Z-Flag wenn not found
		beq.b	CalcEm			; not found ---> Berechnen
		movea.l	d0,a0			; Zeiger auf CAMG....
		move.l	8(a0),d0		; ViewModes
		tst.w	8(a0)			; Oberes WORD == 0 ?
		bne.b	1$			; Nein ---> Nix ausmaskieren
		andi.l	#MODESMASK,d0		; Verbotene Bits ausmaskieren
1$:		bra.b	Ende			; --->

	*** ViewModes aus BMHD berechnen, 0 falls kein BMHD

CalcEm:		movea.l	a2,a1			; IFFFile
		bsr	GetBMHDFunc		; BitMapHeader suchen
	;;	tst.l	d0			; nicht gefunden?
		beq.b	Ende			; dann 0 zurückgeben
		movea.l	d0,a0			; A0 :  BMHD-Struktur
		bsr.b	CalcViewModes		; ViewModes nach D0

	IFD OLDBADHAMPICTURES
		cmpi.b	#6,bmh_nPlanes(a0)	; 6 Bitplanes ?
		blt.b	Ende			; nein --->
		bset	#11,d0			; ViewModes |= HAM
	ENDC
Ende:
		movea.l	(SP)+,a2
		rts


*****i* iff.library/CalcViewModes *******************************************
*
*    NAME
*	CalcViewModes() -- Calculate Amiga-specific ViewModes from a BMHD
*
*    SYNOPSIS
*	viewmodes = CalcViewModes( bmhd )
*	D0                         A0
*
*	ULONG CalcViewModes( struct IFFL_BMHD )
*
*    FUNCTION
*	Tries to calculate the viewmodes for a CAMG chunk by looking at
*	the bmh_Width, bmh_Height and bmh_Depth entries of a bmhd.
*	This is not always satisfactory, but we're stuck with it.
*
*    INPUTS
*	bmhd - BitMapHeader describing the picture's dimensions
*
*    RESULT
*	viewmodes - ULONG containing the view modes (LACE, HIRES)
*
*    BUGS
*	Knows nothing about Monitor IDs or new View modes like SUPERHIRES
*	or HAM8. You should not use this function in new code.
*
*    SEE ALSO
*	IFFL_GetViewModes(), IFFL_SaveClip()
*
*****************************************************************************

CalcViewModes:	moveq.l	#0,d0			; D0 :  ViewModes

		cmpi.b	#4,bmh_nPlanes(a0)	; mehr als 4 Planes ?
		bgt.b	NotHiRes		; ja ---> nicht HiRes

		cmpi.w	#400,bmh_Width(a0)	; Bildbreite > 400 ?
		ble.b	NotHiRes		; nein --->
		bset	#15,d0			; ViewModes |= HiRes
NotHiRes:
		cmpi.w	#320,bmh_Height(a0)	; Bildhöhe > 320 ?
		blt.b	NotInterlace		; nein --->
		bset	#2,d0			; ViewModes |= Interlace
NotInterlace:
		rts


		END