IIgs stencil blitter fixed. Thanks dwsJason!

joeylib/src/jIIgs.asm

@@ -123,130 +123,172 @@ blitTop	ldy	source	; Load Y register with source pixel offset
 
 ;----------------------------------------
 ; Blit an 8x8 block with stencil to (almost) anywhere on a surface.
+; (Thanks dwsJason!)
 ;----------------------------------------
-asmB88a	start
+asmB88a start
 
-source	equ	1	; Source Pixels Offset
-target	equ	3	; Target Pixels Offset
-t	equ	5	; Temp
-xc	equ	7	; X Counter
-yc	equ	9	; Y Counter
-stenO	equ	11	; Stencil Buffer Offset
-stenB	equ	13	; Stencil bit pattern
+source	equ 1	; Source Pixels Offset
+target	equ 3	; Target Pixels Offset
+xc	equ 5	; X Counter
+yc	equ 7	; Y Counter
+mask0123	equ 9
+stoffset	equ 11
+tile_pix	equ 13
+
+	jsubroutine (4:surface,4:tiles,4:stencil,2:sx,2:sy,2:tx,2:ty),16
 
-	jsubroutine (4:surface,4:tiles,4:stencil,2:sx,2:sy,2:tx,2:ty),14
 	using GlobalData
-
 ; Find offset into tile memory
 ; Divide source horizontal position by two since there are two pixels per byte
 	lda	sx	; Load X source position into accumulator
 	lsr	a	; Shift Right - divide by 2
-	sta	t
-	clc
+	tax		; save in temp
+
+; c=? but does not matter
 	lda	sy	; Load sy to get index into scanline table
 	asl	a	; Multiply by two to get offset into scanline table (two bytes per entry in table)
 	tay
-	clc
-	lda	ScTable,y	; Load byte offset of y position from table
-	adc	t	; Add t to scanline offset
-	sta	source	; Offset to start of source pixels
+	txa
+	adc	ScTable,y	; Load byte offset of y position from table
+; c=0 from the asl above here
+	sta	source	; Offset to start of source pixels; Find offset into target surface memory
 
 ; Divide target horizontal position by two since there are two pixels per byte
-	lda	tx	; Load X target position into accumulator
-	lsr	a	; Shift Right - divide by 2
-	clc
-	sta	tx	; Store it back into tx
+	lsr	tx
 
-; Find offset into target surface memory
 	lda	ty	; Load ty to get index into scanline table
 	asl	a	; Multiply by two to get offset into scanline table (two bytes per entry in table)
 	tay
 	lda	ScTable,y	; Load byte offset of y position from table
+; c=0 from the asl above
 	adc	tx	; Add x position to scanline offset
-	sta	target	; Offset to start of target pixels
+	sta	target	; Offset to start of target pixels; Find the upper left corner of the stencil
 
-; Find starting stencil byte
-;***FIX*** Does not handle non-byte boundaries!
-	clc
-	lda	sy	; Vertical cell position
-	asl	a	; Multiply by two to get offset into stencil table (two bytes per entry in table)
-	tay		; Move to Y
-	lda	StTable,y	; Load offset location of start of this row in the stencil buffer
-	adc	sx	; Add x position to address offset
-	sta	stenO	; Offset to start of mask data
+	lda	sy
+	asl	a
+	tay
+	lda	ScTable,y   ; look up in the pixel scanline table
+	lsr	a
+	lsr	a	   		; we're 4 times smaller, so just divide it
+	sta	stoffset
 
 	lda	#0	; Load 0 into X and Y counters
 	sta	xc
 	sta	yc
 
-stenTop	ldy	stenO	; Load byte at stencil offset
-	lda	[stencil],y
-	xba		; Shift it into the high byte
-	sta	stenB	; Put it in to the stencil byte
+blitTop anop
+; build the mask
+	lda	#$FFFF
+	sta	mask0123   ; default all 4 pixels visible
 
-blitTop	lda	stenB	; Load stencil bit pattern
-	tax		; Copy to x
-	asl	a	; Shift up a nibble for next time
-	asl	a
-	asl	a
-	asl	a
-	sta	stenB	; Save for next pass
-	txa		; Load original stencil byte back back
-	xba		; Flip what we want into LSB
-	and	#$00f0	; Mask off top nibble
-	lsr	a	; Shift it down to low nibble but multiplied by 2
+	lda	sx     	   ; add in stencil X position
 	lsr	a
 	lsr	a
-;	lsr	a
-	tay		; Put it in y
-	lda	MaTable,y	; Load mask word
-; Draw four pixels
-	ldy	target	; Load Y register with target pixel offset
-	and	[surface],y	; AND target pixels with mask word
+	lsr 	a	   		; div by 8 to get to byte index
+	clc
+	adc	stoffset
+	tay
+
+	lda	sx
+	and	#7
+; A = number of initial bits to shift out
+; to get to the mask
+    	tax			   ; save in X
+
+	lda [stencil],y ; load the stencil
+
+	xba             ; since we divided by 8, need to get our bits up high
+skipbit anop 		; burn bits we don't care about
+	asl	a
+	dex
+	bpl	skipbit
+
+	tax
+	bcc	mask0   	; bit clear, leave mask alone
+	lda	#$00F0  	; bit set, set the mask bits
+	trb	mask0123
+mask0 anop
+	txa
+	asl	a
+	tax
+	bcc	mask1       ; bit clear, leave mask alone
+	lda	#$000F      ; bit set, set the mask bits
+	trb	mask0123
+mask1	anop
+	txa
+	asl	a
+	tax
+	bcc	mask2       ; bit clear, leave mask alone
+	lda	#$F000      ; bit set, set the mask bits
+	trb	mask0123
+mask2 anop
+	txa
+	asl	a
+	bcc	mask3       ; bit clear, leave mask alone
+	lda	#$0F00      ; bit set, set the mask bits
+	trb	mask0123
+mask3 anop
+; c=?
+	clc		; c=0
+	lda	sx
+	adc	#4 	; Add 4 here because we're moving left to right
+	sta	sx
+
 	ldy	source	; Load Y register with source pixel offset
-	ora	[tiles],y	; OR with source pixels
-	ldy	target	; Load Y register with target pixel offset
-	sta	[surface],y	; Store 4 pixels into screen
+	lda	[tiles],y	; Load 4 tile pixels
+	sta	tile_pix
 
-	clc		; Increment to next pixel target quad
+	ldy	target	; Load Y register with target pixel offset
+	lda	[surface],y
+ 	and	mask0123
+	ora	tile_pix
+
+	sta	[surface],y	; Store 4 pixels into screen
+;clc		; Increment to next pixel target quad
 	lda	#2
 	adc	target
 	sta	target
-	clc		; Increment to next pixel source quad
+; c=0 here as long as target didn't go over $FFFF
+;clc		; Increment to next pixel source quad
 	lda	#2
 	adc	source
-	sta	source
-
-	clc
+	sta	source	;clc  ; c=0 here as long as source didn't go above $FFFF
 	lda	xc	; Increment X counter
 	adc	#1
 	sta	xc
 	cmp	#2	; End of X pixels?
-	bcc	blitTop	; Nope!
+	bcc	blitTop	; Nope!	lda	#0	; Reset X counter
 
-	lda	#0	; Reset X counter
-	sta	xc
-	clc		; Increment target offset
-	lda	#156
+	stz	xc	; reset xcounter to 0
+; c = 1
+; reset stencil X
+	lda	sx
+	sbc	#8
+	sta	sx
+
+; c=0
+	clc
+	lda	stoffset   ;Increment Stencil offset
+	adc	#40     ; 160 / 4
+	sta	stoffset	; c=0		; Increment target offset
+
+	lda	#156    ; c=1, so instead of doing clc, adc 156, just do adc 155
 	adc	target
 	sta	target
-	clc		; Increment source offset
+;clc		; Increment source offset
+; c=0 unless target goes above $FFFF
 	lda	#156
 	adc	source
 	sta	source
-	clc		; Increment stencil mask offset
-	lda	#40
-	adc	stenO
-	sta	stenO
-	clc
+; clc   c=0 unless source goes above $FFFF
 	lda	yc	; Increment Y counter
 	adc	#1
 	sta	yc
 	cmp	#8	; End of Y pixels?
-	bcs	blitDone	; Yep!
-	brl	stenTop	; Back for more
-
-blitDone	jreturn
+	bcs	maskend	; Yep!
+	jmp	blitTop
+maskend	anop
+	jreturn
 	end
 
 

joeylib/src/jIIgs.c

@@ -157,19 +157,25 @@ bool jlGameGetButton(byte which) {
 
 
 bool _jlImgCreate(jlImgT **img) {
-	jlImgT *t = (jlImgT *)jlMalloc(sizeof(jlImgT));
-	if (t != NULL) {
-		memset(t, 0, sizeof(jlImgT));
-		t->id[0] = 'I';
-		t->id[1] = 'M';
-		t->id[2] = 'G';
-		t->version = 0;
-		memcpy(t->palette, SHRCOLORS, sizeof(t->palette));
-		memcpy(t->pixels, SHRPIXELS, sizeof(t->pixels));
+	jlImgT *t = NULL;
+
+	// Are we loading into a new image?
+	if (*img == NULL) {
+		t = (jlImgT *)jlMalloc(sizeof(jlImgT));
+		if (t == NULL) {
+			return false;
+		}
 		*img = t;
-		return true;
 	}
-	return false;
+	memset(t, 0, sizeof(jlImgT));
+	t->id[0] = 'I';
+	t->id[1] = 'M';
+	t->id[2] = 'G';
+	t->version = 0;
+	memcpy(t->palette, SHRCOLORS, sizeof(t->palette));
+	memcpy(t->pixels, SHRPIXELS, sizeof(t->pixels));
+	*img = t;
+	return true;
 }
 
 

joeylib/src/jSDL2.c

@@ -199,9 +199,6 @@ void jlDrawBlit8x8a(jlSurfaceT source, jlStnT *stencil, jint16 sx, jint16 sy, ji
 	//   Color = <-- 40 tiles, 80 bytes, 160 pixels -->
 	// Stencil = <-- 20 bytes, 160 bits -->
 
-	i = so / 8;
-	pos = 7 - (so % 8);
-
 	for (y=0; y<8; y++) {
 		for (x=0; x<4; x++) {
 
@@ -415,22 +412,28 @@ bool jlGameGetButton(byte which) {
 
 
 bool _jlImgCreate(jlImgT **img) {
-	jlImgT *t = (jlImgT *)jlMalloc(sizeof(jlImgT));
-	if (t != NULL) {
-		memset(t, 0, sizeof(jlImgT));
-		t->id[0] = 'I';
-		t->id[1] = 'M';
-		t->id[2] = 'G';
-		t->version = 0;
-		// Backing store does not exist at startup
-		if (_jlBackingStore != NULL) {
-			memcpy(t->palette, _jlBackingStore->palette, sizeof(t->palette));
-			memcpy(t->pixels, _jlBackingStore->pixels, sizeof(t->pixels));
+	jlImgT *t = NULL;
+
+	// Are we loading into a new image?
+	if (*img == NULL) {
+		t = (jlImgT *)jlMalloc(sizeof(jlImgT));
+		if (t == NULL) {
+			return false;
 		}
 		*img = t;
-		return true;
 	}
-	return false;
+	memset(t, 0, sizeof(jlImgT));
+	t->id[0] = 'I';
+	t->id[1] = 'M';
+	t->id[2] = 'G';
+	t->version = 0;
+	// Backing store does not exist at startup
+	if (_jlBackingStore != NULL) {
+		memcpy(t->palette, _jlBackingStore->palette, sizeof(t->palette));
+		memcpy(t->pixels, _jlBackingStore->pixels, sizeof(t->pixels));
+	}
+	*img = t;
+	return true;
 }