Differences

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--- scoring_points [2015-04-17 04:35] – external edit 127.0.0.1
+++ scoring_points [2015-10-07 22:10] (current) – removed ftc
@@ Line 1: / Line 1: @@
-====== Scoring points ======
-by Achim
-There're three ways to code scoring.
-===== 1) Decimal mode =====
-This one can be found in many games. You only have to declare
-a couple of variables for the player's score and switch to decimal
-mode.
-Example for six digits:
-<code>
-sed		//set decimal mode
-clc
-lda #$50	//50 points scored
-adc score1	//ones and tens
-sta score1
-lda score2	//hundreds and thousands
-adc #00
-sta score2
-lda score3	//ten-thousands and hundred-thousands
-adc #00
-sta score
-cld		//clear decimal mode
-</code>
-The score can now be printed on screen:
-<code>
-lda score3
-and #$f0	        //hundred-thousands
-lsr
-lsr
-lsr
-lsr
-ora #$30		// -->ascii
-sta screenposition	//print on screen
-lda score3
-and #$0f		//ten-thousands
-ora #$30		// -->ascii
-sta screenposition+1	//print on next screen position
-lda score2		//same procedure for all digits
-...
-</code>
-Switching to decimal mode can cause problems under certain conditions:
-Let's say an irq kicks in to write sprite registers while decimal mode is set.
-This would mess up all registers, of course.
-This might happen with a sprite mulitplexer, because these irqs are
-unpredictable. Idea would be to start these irqs with
-CLD. Another would be to disable irqs while calculating.
-===== 2) Hexadecimal mode =====
-Not much to explain. Declare your variables for the score. Use a standard hexadecimal addition
-and print the result on screen (preferably with a routine like [[base:32_bit_hexadecimal_to_decimal_conversion|this]], which converts hexadecimal to decimal, then ascii).
-===== 3) ASCII =====
-This one's most commonly used in games. Each ascii code on screen is treated like a digit.
-An addition would look like this:
-<code>
-		ldx #$05
-		lda #$00
-!:		sta carry,x		//clear carry table
-		dex
-		bpl !-
-		ldx #$05		//6 digits
-!:		lda figure1,x           //current score, usually located in screen memory
-		clc
-		adc figure2,x           //add points
-		adc carry,x
-		and #$0f		//check bits0-3
-		cmp #$0a		//if >=10
-		bcc nocarry
-		inc carry-1,x		//then set carry for next digit...
-		sec
-		sbc #$0a		//... -10 for correct ascii
-nocarry:	ora #$30		//-->ascii
-		sta sum,x
-		dex
-		bpl !-
-		rts
-figure1:	.byte		$31, $32, $30, $33, $37, $39 		//   120379 (example)
-figure2:	.byte		$32, $32, $30, $39, $32, $31 		//  +220921
-carry:		.byte		$00, $00, $00, $00, $00, $00		//tmp for carry
-sum:		.byte		$00, $00, $00, $00, $00, $00
-</code>