Only recompile affected terrain rows for cratering

projectile.s

@@ -877,7 +877,7 @@ processPlayerImpactDeath:
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; processTerrainImpact
 ;
-; Trashes A,Y
+; Trashes A,Y, SCRATCHL
 ;
 processTerrainImpact:
 	ldy projectileActive
@@ -888,17 +888,19 @@ processTerrainImpact:
 
 	lda projectileData+GO_POSX,y
 	clc
-	adc #GAMEOBJECTWIDTH/2			; /2 is a fudge that makes crater location look better in this direction
+	adc #GAMEOBJECTWIDTH/2+1			; A fudge that makes crater location look better in this direction, and tunneling work better
 	bra processTerrainStoreContinue
 
 processTerrainImpactNegative:
 	lda projectileData+GO_POSX,y
+	clc
+	adc #GAMEOBJECTWIDTH/4-1			; A fudge that makes crater location look better in this direction, and tunneling work better
 
 processTerrainStoreContinue:
 	sta PARAML0
 	lda projectileData+GO_POSY,y
 	sec
-	sbc #GAMEOBJECTHEIGHT
+	sbc #GAMEOBJECTHEIGHT	; This fudge makes tunneling work better
 	sta PARAML1
 
 	lda projectileData+JD_TYPE,y
@@ -907,9 +909,29 @@ processTerrainStoreContinue:
 
 	lda projectileTypes+PT_RADIUS,y
 	tay
+	phy					; We'll need the radius in a moment
 
 	jsr craterTerrain
-	jsr compileTerrain
+
+	jsr unclipTerrain	
+
+	; Recompile the rows affected by the crater
+	clc
+	lda PARAML1			; Impact point is top row to recompile
+	adc #GAMEOBJECTHEIGHT	; Expand recompile area upwards because of tunneling fudge
+	tax
+
+	clc
+	pla
+	adc #GAMEOBJECTHEIGHT	; Expand "vertical" radius area because of tunneling fudge
+	sta SCRATCHL		; Need radius in a memory location for this math
+	txa
+	sec
+	sbc SCRATCHL
+	tay
+	lda SCRATCHL
+	jsr compileTerrainChunk
+
 	jsr clipTerrain
 
 	rts

terrain.s

@@ -271,11 +271,50 @@ compileTerrainLoop:
 	bra compileTerrainLoop
 
 compileTerrainDone:
-	;jsl compileTerrainSpans	; Part of the now disabled fill-mode renderer
 	RESTORE_AY
 	rts
 
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; compileTerrainChunk
+;
+; Y = First row to compile (bottom-relative)
+; X = Last row to compile (bottom-relative)
+; A = |X-Y|
+;
+; Trashes A,Y, SCRATCHL
+;
+compileTerrainChunk:
+;HARDBRK
+	stx SCRATCHL
+	sty PARAML0
+
+	; Compute the start of memory affected
+	lda #COMPILEDTERRAINROW
+	sta PARAML1
+	jsr mult16
+	clc
+	adc #compiledTerrain
+	sta PARAML0
+
+compileTerrainChunkLoop:
+	sty PARAML1
+;HARDBRK
+	jsr compileTerrainRow
+	iny
+	cpy SCRATCHL
+	beq compileTerrainChunkDone
+
+	clc
+	lda #COMPILEDTERRAINROW
+	adc PARAML0
+	sta PARAML0
+	bra compileTerrainChunkLoop
+
+compileTerrainChunkDone:
+	rts
+
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; compileTerrainRow
 ;

utility.s

@@ -106,7 +106,8 @@ intToStringResult: .byte 0,0,0,0,0,0
 ; PARAML1 = Operand 2 (16 bits)
 ; A => Op1 * Op2 (16 bits)
 ; Algorithm from https://apple2.gs/downloads/Programmanual.pdf
-; Trashes X
+;
+; Trashes X,PARAML0,PARAML1
 ;
 mult16:
 	lda #0			; Initialize result