Extra half brite example

011.ehb_mode/Makefile

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+NUM_COLORS=64
+MODULE=ehb_mode.s
+FLOPPY=bin/ehb_mode.adf
+IMAGEDATA=out/image-palette.s out/image.bin
+IMAGEFILE=../assets/gigi.png
+EXTRA=$(IMAGEDATA) $(BOB_IMAGEDATA) init.s utils.s constants.i Makefile
+VASM_EXTRA_ARGS=-DSCREEN_COLORS=$(NUM_COLORS)
+
+ifeq ($(NUM_COLORS),64)
+EXTRA_HALF_BRITE=--extra-half-brite
+endif
+
+include ../shared/base.mk
+
+$(IMAGEDATA): $(IMAGECON) $(IMAGEFILE) $(SHARED_PALETTE) Makefile
+	$(IMAGECON) --input $(IMAGEFILE) --output out/image --output-bitplanes --output-grey-palette-asm --output-palette-asm --colors=32 --quantize $(EXTRA_HALF_BRITE)

011.ehb_mode/README.md

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+Extra half brite mode
+=====================
+
+[Extra half brite mode](http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node0098.html) allows us to use 32 colors as well as 32 "half brite" versions of those colors.
+
+I basic supprt to [imagecon](../tools/imagecon) to output EHB mode data.  It doesn't really do a great job of taking advantage of the EHB mode.
+
+The only changes I made to the asm code to allow EHB mode was to add the 6th bitplane and make sure the copper reset the extra bitplane pointer.
+
+We can see from the output that it's not earth shatteringly different.  I think if you developed an image with EHB in mind, then imagecon would generate the correct data...  maybe ;-) I will test this at some stage.
+
+64 extra half brite
+-------------------
+![6 bitplanes](screenshots/64-colors.png?raw=true)
+
+32 colors
+---------
+![5 bitplanes](screenshots/32-colors.png?raw=true)
+
+The differences
+---------------
+![image differences](screenshots/diff.png?raw=true)
+
+[Download disk image](bin/ehb_mode.adf?raw=true)
+
+

011.ehb_mode/constants.i

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+LVL3_INT_VECTOR		equ $6c
+SCREEN_WIDTH		equ 320
+SCREEN_HEIGHT		equ 256
+SCREEN_WIDTH_BYTES	equ (SCREEN_WIDTH/8)
+			if SCREEN_COLORS == 64
+SCREEN_BIT_DEPTH	equ 6
+			endif
+			if SCREEN_COLORS == 32
+SCREEN_BIT_DEPTH	equ 5
+			endif
+			if SCREEN_COLORS == 16
+SCREEN_BIT_DEPTH	equ 4
+			endif
+			if SCREEN_COLORS == 8
+SCREEN_BIT_DEPTH	equ 3
+			endif
+			if SCREEN_COLORS == 4
+SCREEN_BIT_DEPTH	equ 2
+			endif
+			if SCREEN_COLORS == 2
+SCREEN_BIT_DEPTH	equ 1
+			endif
+SCREEN_RES		equ 8 	; 8=lo resolution, 4=hi resolution
+RASTER_X_START		equ $81	; hard coded coordinates from hardware manual
+RASTER_Y_START		equ $2c
+RASTER_X_STOP		equ RASTER_X_START+SCREEN_WIDTH
+RASTER_Y_STOP		equ RASTER_Y_START+SCREEN_HEIGHT

011.ehb_mode/ehb_mode.s

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+	include "../include/registers.i"
+	include "hardware/dmabits.i"
+	include "hardware/intbits.i"
+	
+	include "constants.i"
+	
+entry:
+	lea 	CUSTOM,a6
+	bsr	init
+	bsr.s	installColorPalette
+	
+.mainLoop:
+	bsr 	waitVerticalBlank
+	bra	.mainLoop
+	
+	include "init.s"
+	include "utils.s"
+	
+installColorPalette:
+	include "out/image-palette.s"
+	rts
+
+copper:
+	;; bitplane pointers must be first else poking addresses will be incorrect
+	dc.w	BPL1PTL,0
+	dc.w	BPL1PTH,0
+	dc.w	BPL2PTL,0
+	dc.w	BPL2PTH,0
+	dc.w	BPL3PTL,0
+	dc.w	BPL3PTH,0
+	dc.w	BPL4PTL,0
+	dc.w	BPL4PTH,0
+	dc.w	BPL5PTL,0
+	dc.w	BPL5PTH,0
+	dc.w	BPL6PTL,0
+	dc.w	BPL6PTH,0
+
+	dc.l	$fffffffe	
+
+bitplanes:
+	incbin	"out/image.bin"

011.ehb_mode/init.s

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+	;; custom chip base globally in a6
+init:
+	movem.l	d0-a6,-(sp)
+	move	#$7ff,DMACON(a6)	; disable all dma
+	move	#$7fff,INTENA(a6) ; disable all interrupts	
+
+	;; set up default palette
+	bsr.s	installColorPalette
+	
+	;; set up playfield
+	move.w  #(RASTER_Y_START<<8)|RASTER_X_START,DIWSTRT(a6)
+	move.w	#((RASTER_Y_STOP-256)<<8)|(RASTER_X_STOP-256),DIWSTOP(a6)
+
+	move.w	#(RASTER_X_START/2-SCREEN_RES),DDFSTRT(a6)
+	move.w	#(RASTER_X_START/2-SCREEN_RES)+(8*((SCREEN_WIDTH/16)-1)),DDFSTOP(a6)
+	
+	move.w	#(SCREEN_BIT_DEPTH<<12)|$200,BPLCON0(a6)
+	move.w	#SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH-SCREEN_WIDTH_BYTES,BPL1MOD(a6)
+	move.w	#SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH-SCREEN_WIDTH_BYTES,BPL2MOD(a6)
+
+	;; poke bitplane pointers
+	lea	bitplanes(pc),a1
+	lea     copper(pc),a2
+	moveq	#SCREEN_BIT_DEPTH-1,d0
+.bitplaneloop:
+	move.l 	a1,d1
+	move.w	d1,2(a2)
+	swap	d1
+	move.w  d1,6(a2)
+	lea	SCREEN_WIDTH_BYTES(a1),a1 ; bit plane data is interleaved
+	addq	#8,a2
+	dbra	d0,.bitplaneloop
+
+	;; install copper list, then enable dma and selected interrupts
+	lea	copper(pc),a0
+	move.l	a0,COP1LC(a6)
+ 	move.w  COPJMP1(a6),d0
+	move.w	#(DMAF_BLITTER|DMAF_SETCLR!DMAF_COPPER!DMAF_RASTER!DMAF_MASTER),DMACON(a6)
+	;; move.w	#(INTF_SETCLR|INTF_VERTB|INTF_INTEN),INTENA(a6)
+	movem.l (sp)+,d0-a6
+	rts

011.ehb_mode/utils.s

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+waitVerticalBlank:	
+	movem.l d0-a6,-(sp)
+.loop	move.l	$dff004,d0
+	and.l	#$1ff00,d0
+	cmp.l	#303<<8,d0
+	bne.b	.loop
+	movem.l (sp)+,d0-a6
+	rts	
+
+
+
+waitRaster:		;wait for rasterline d0.w. Modifies d0-d2/a0.
+	movem.l d0-a6,-(sp)
+	move.l #$1ff00,d2
+	lsl.l #8,d0
+	and.l d2,d0
+	lea $dff004,a0
+.wr:	move.l (a0),d1
+	and.l d2,d1
+	cmp.l d1,d0
+	bne.s .wr
+	movem.l (sp)+,d0-a6
+	rts