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--- base:decrease_x_register_by_more_than_1 [2015-04-17 04:31] – external edit 127.0.0.1
+++ base:decrease_x_register_by_more_than_1 [2017-03-29 08:01] – [Fill sprite with vertical pattern (containing $ff, $7f, $3f)] shrydar
@@ Line 40: / Line 40: @@
 Another property of the SBX opcode is that it doesn't respeect the decimal mode, since it is derived from CPX rather than SBC. So if you need to perform table lookups and arithmetic in a tight interrupt routine there's no need to clear the decimal flag in case you've got some code running that operates in decimal mode.
+====== Examples ======
+===== Fill sprite with vertical pattern (containing $ff, $bf, $7f, $3f) =====
+<code>
+ldx #60
+fs
+lda #xx
+sta spr+o0,x
+lda #yy
+sta spr+o1,x
+lda #$ff or $bf or $7f or $3f
+sta spr+o2,x
+axs#3
+bpl fs
+rts
+</code>
+where o0,o1,o2 is an excluding choice of {0,1,2}.
+On one column of the sprite a must contain $ff, $bf, $7f or $3f, because if it is anded with the value of the x reg, x must be preserved. As x runs from 60 to 0 (where 63 is $3f) this is only the case for these four values.
 ===== Info on SBX/AXS on external sites =====
   * [[http://unusedino.de/ec64/technical/aay/c64/bsbx.htm|Ninjas reference]]
   * [[http://www.oxyron.de/html/opcodes02.html|Grahams reference]]