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+====== Merge char bullets with background chars ======
+by Achim
+Char bullets look quite ugly when flying around. A way to achieve a more aesthetic look is to generate new chars on the fly everytime the bullet's moving one char ahead.
+First thing to do is to reserve as many empty chars in your charset as you need bullets in your game.
+For example 8 chars:
+<code>
+charset:	$2000-$2800
+empty chars:	$27c0, $27c8, $27d0, $27d8, $27e0, $27e8, $27f0, $27f8
+char values:	$f8, $f9, $fa, $fb, $fc, $fd, $fe, $ff
+</code>
+Now you need a positive and a negative image/char of your char bullet.\\
+\\
+Negative image\\
+{{:base:negativechar.gif?200|}}\\
+Positive image\\
+{{:base:positivechar.gif?200|}}
+The negative has to be done with $d021 and $d800/colorRAM, the positive should be done with $d022 and/or $d023.
+$d800 should only be used for the positive when all chars got the same color RAM. Otherwise the bullets
+change their color accordingly everytime they move ahead which might look stupid.
+Everytime the main program places a new bullet on screen respectively moving the char bullet on screen,
+it first has to read and save the char underneath the bullet.
+<code>
+ldy screencolumn	//column of char bullet
+lda (screenposition),y	//screenposition=zp address holding the screen row
+sta charstorage,x	//save char at specific position, x pointing at currently used char bullet
+jsr chargenerator	//now create new char and print it on screen
+</code>
+Now the new char has to be generated:
+<code>
+.const charsethibyte	= $20		/charset at $2000
+.const negativechar 	= $2008		//2. char in charset
+.const positivechar 	= $2010		//3. char in charset
+//acc still holding value of saved char
+//x-reg still pointing at currently used char bullet
+//y-reg still holding current screen column
+chargenerator:	asl		        //figure out chardata of saved char
+		asl
+		asl
+		sta tmp0		//get low byte of chardata in charset -> tmp0=zp address
+		lda (screenposition),y
+		lsr
+		lsr
+		lsr
+		lsr
+		lsr
+		clc
+		adc #charsethibyte	//charset located at $2000
+		sta tmp1		//get hi byte of chardata in charset
+		lda charsetposition,x	//fetch low byte of new chardata to be written
+		sta writechar+1		//selfmod
+		ldy #$07
+!:		lda (tmp0),y		//read chardata from charset
+genand:		and negativechar,y	//use negative char to punch a hole into chardata
+genora:		ora positivechar,y	//and fill it with positive chardata
+writechar:	sta $2700,y		//write new chardata (low byte: selfmodifying code, mind the hi byte)
+         	dey
+		bpl !-
+		lda newcharvalue,x	//get char value of new char bullet
+		ldy screencolumn	//column of char bullet
+		sta (screenposition),y	//print new char bullet on screen
+		rts
+charsetposition:	.byte		$c0, $c8, $d0, $d8, $e0, $e8, $f0, $f8		//low bytes
+newcharvalue:		.byte		$f8, $f9, $fa, $fb, $fc, $fd, $fe, $ff
+</code>
+Check out these games to see how it looks:
+http://csdb.dk/release/?id=16770
+http://csdb.dk/release/?id=105361