```
HandleTileCollision:
;;;;;ASSUMES vulnerability bit 000x0000, if one, skips collision.
;;;;;Six collision points.
;;;;;All collision points checked and registered for all objects.
;;;; a solid in any of the points will result in negating all others.
;;; There are 6 ram variables, collisionPoint0 - collisionPoint5.
;;; collisionPoint0 = top left
;;; collisionPoint1 = top right
;;; collisionPoint2 = bottom right
;;; collisionPoint3 = bottom left.
;;; collisionPoint4 = mid left
;;; collisionPoint5 = mid right.
TXA
STA currentObject
TYA
STA tempy
LDA npc_collision
AND #%11111101
LDA #$00
STA npc_collision
LDA navFlag
AND #%11111110
STA navFlag
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; EXPLANATION:
;; In this basic module, both non gravity and gravity scripts are loaded.
;; Under most circumstances, a user will likely make use of one or the other,
;; as they each take up a good chunk of data. But the benefit of including both is that
;; a platforming game with gravity is just a simple bit flip in the screen flags.
LDA screenFlags
AND #%00100000
BNE useGravity
JMP dontUseGravity
useGravity:
LDA Object_vulnerability,x
AND #%00100000
BEQ useGravity2
LDA Object_physics_byte,x
AND #%00000010
BNE useGravity2
JMP dontUseGravity
useGravity2:
;;;;;;===================================================
;;;;;;***************************************************
;;;;;; TILE COLLISION FOR SCROLLING PLATFORMERS:
;;;;;; For scrolling platformers we will use three types of collision detection:
;;;;;; 1. A routine to check under our feet to determine
;;;;;; whether or not you are standing on a solid object.
;;; This function will check under neath the object's feet
;;; by arg0 pixels.
;;; it will update bit 0 of the Object_physics_byte.
;;; If that bit is 0, it means the place is free.
;;; If that bit is 1, it means the place is solid.
;**********************
CheckUnderObject #$01
;;;;;;
;;;;;; 2. A routine that checks to see if the potential position leaves you
;;;;;; with your 'bottom' or 'top' in a solid object, in which case it ejects pixel perfect
;;;;;; to that tile.
;;; This function checks the POTENTIAL vertical position.
;;; If it results in a point in a solid object, it appropriately
;;; ejects and places the object directly against the point
;;; of collision.
; **********************
CheckForVerticalEjection
;;;;;; Better check for any vertical updates now, or else
;;;;;; a horizontal collision could cancel out the required
;;;;;; bounds update
CheckPlayerCameraPositionVertical
;;;;;;
;;;;;; 3. A routine which checks horizontal motion to see if the potential position
;;;;;; sees a solid collision, in which case it can not move.
;;; This function checks potential horizontal position.
;;; without factoring in vertical motion. If it sees a solid,
;;; it skips motion.
; ***********************
CheckForHorizontalCollision
;;;; This is the end of scrolling platform physics. It automatically jumps to the proper place.
;;;; Otherwise, if there was no collision, we jump to updating the position.
;; we only need to update horizontal position
CheckPlayerCameraPositionHorizontal
;;;; if it turns out we were outside of the camera bounds, the macro
;;;; has RTSed out of this routine, so the hoziontal position will
;;;; never be updated.
JSR updateHorizontalPosition
JMP DoneWithTileChecksAndUpdatePosition
;;;;;;;;;;;;;==============================================
dontUseGravity:
CheckPotentialPosition
CheckPlayerCameraPositionHorizontal
JSR updateHorizontalPosition
CheckPotentialPosition
CheckPlayerCameraPositionVertical
JSR updateVerticalPosition
JMP DoneWithTileChecksAndUpdatePosition
JMP DoneWithTileChecksAndUpdatePosition
;;; NO POINTS WERE SOLID
;;;; update hold
DoneWithTileChecksAndUpdatePosition:
ldx currentObject
RTS
HandleSolidCollision:
LDA screenFlags
AND #%00000100 ;; is it autoscrolling?
BEQ + ;; not autoscrolling
;;; is auto scrolling
CPX player1_object
BNE +
JSR CheckAutoScrollLeftEdge
RTS
+ ;; not auto scrolling.
LDA xPrev
STA xHold_hi
LDA yPrev
STA yHold_hi
TYA
STA tempy
LDA Object_edge_action,x
LSR
LSR
LSR
LSR
BEQ doNothingAtSolid
TAY
LDA AI_ReactionTable_Lo,y
STA temp16
LDA AI_ReactionTable_Hi,y
STA temp16+1
JSR doReactionTrampolineSolid
JMP pastReactionTrampolineSolid
doReactionTrampolineSolid:
JMP (temp16) ;;; this now does the action
;; and when it hits the RTS in that action,
;; it will jump back to the last JSR it saw,
;; which was doNewActionTrampoline...which will immediately
;; jump to pastDoNewActionTrampoline.
pastReactionTrampolineSolid:
;LDA #$00
;STA xHold_lo
doNothingAtSolid:
;;;;;;;;;;; Do solid reaction type.
LDY tempy
LDX currentObject
RTS
ejectUp:
LDA tileY
and #%00001111;We can only be 0 to 15 pixels in any given wall
sta temp
lda Object_y_hi,x
clc;Subtract one plus that so we're a pixel out of the wall rather than one pixel in it.
SBC temp
STA Object_y_hi,x
LDA #$00
STA yHold_lo
STA Object_v_speed_hi,x
STA Object_v_speed_lo,x
RTS
ejectDown:
lda tileY
and #%00001111;we can only be 0 to 15 pixels in any given wall
eor #%00001111;If we're at position 15 in the tile, we only want to eject 0 (+1) so flip the bits
sec;Will add the extra one to the position so that we're a pixel out of the wall
adc Object_y_hi,x;rather than one pixel in it.
sta Object_y_hi,x
LDA #$00
STA yHold_lo
STA Object_v_speed_hi,x
STA Object_v_speed_lo,x
;;; check the top two collision points to see if is it a prize block.
LDA collisionPoint0
CMP #COL_INDEX_PRIZE_BLOCK
BEQ +
JMP ++
+
LDA Object_x_hi,x
CLC
ADC Object_left,x
STA tileX
JMP +++
++
LDA collisionPoint1
CMP #COL_INDEX_PRIZE_BLOCK
BEQ +
JMP ++
+
LDA Object_x_hi,x
CLC
ADC Object_right,x
STA tileX
+++
LDA gameHandler
ORA #%00010000
STA gameHandler
;;;;; check other head-hit type objects here.
;; change collision data.
;; should still have the correct coordinates in tileX and tileY
ChangeTileAtCollision #$00, #TILE_INDEX_PRIZE_OFF
TXA
PHA
LDA Object_x_hi,x
STA temp
LDA Object_y_hi,x
SEC
SBC #$12 ;; a bit more than the height of it.
STA temp1
LDA Object_scroll,x
STA temp2
CreateObject temp, temp1, #OBJ_PRIZE, #$00, temp2
LDA #$00
SEC
SBC #$04
STA Object_v_speed_hi,x
PLA
TAX
++
RTS
CheckForCollision:
;;;; commonly, we won't want to waste cycling 6 times through this for each object when
;;;; all points are at no collision. If by chance we NEED the zero type collision to do something,
;;;; we can comment out the zero type check in this next line. But most games are going to have
;;;; at least one "blank tile" that does nothing, and most games will use zero for this.
;;;; Another conundrum is that a collision could take place in the current or new nametable.
;;;; if this collision is of type that draws from screen data (for instance, NPC data or warp data), it could
;;;; be problematic, as all variables handling these things are loaded with the current collision tables data.
;;;; tempCol ends up being 0 or 1 based on which collision table this should be referencing.
STA temp
BNE notZeroTypeCollision
JMP zeroTypeCollision
notZeroTypeCollision:
LDA #$00
STA tile_solidity
DoCheckPointsLoop:
LDA temp
TAY
LDA tileTypeBehaviorLo,y
STA temp16
LDA tileTypeBehaviorHi,y
STA temp16+1
JSR UseTileTypeTrampoline
JMP pastTileTypeTrampoline
UseTileTypeTrampoline:
JMP (temp16)
pastTileTypeTrampoline:
DontCheckTileType0:
zeroTypeCollision:
ldx currentObject
RTS
DetermineCollisionTable:
LDA tempCol
BNE colPointInDifferentTable
;;;; the collision point is in the current collision table.
LDA Object_scroll,x
AND #%00000001
BNE isInOddTable
JMP isInEvenTable
colPointInDifferentTable:
;;; the collision point to be checked is in the NEXT collision table.
LDA Object_scroll,x
AND #%00000001
BNE isInEvenTable
JMP isInOddTable
isInEvenTable:
LDA collisionTable,y
RTS
isInOddTable:
LDA collisionTable2,y
RTS
updateHorizontalPosition:
LDA xHold_lo
STA Object_x_lo,x
LDA xHold_hi
STA Object_x_hi,x
LDA nt_hold
CMP Object_scroll,x
BEQ justUpdateScroll
LDA #$01
STA update_screen_data_flag
LDA nt_hold
justUpdateScroll:
STA Object_scroll,x
RTS
updateVerticalPosition:
LDA yHold_lo
STA Object_y_lo,x
LDA yHold_hi
STA Object_y_hi,x
RTS
```