Fix collision physics for reverse gravity

mdsteele · Jul 1, 2024 · e9577b2 · e9577b2
1 parent dfa3084
commit e9577b2
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Showing 3 changed files with 69 additions and 25 deletions.
diff --git a/src/avatar.asm b/src/avatar.asm
@@ -263,13 +263,30 @@ _SetPoseInWater:
     sta Zp_AvatarPose_eAvatar
     rts
 _SetPoseOnGround:
-    ;; TODO: Invert Up and Down buttons if gravity is reversed.
+    ;; If gravity is normal, use Down to kneel and Up to look; if gravity is
+    ;; reversed, use Down to look and Up to kneel.
+    lda Zp_P1ButtonsHeld_bJoypad
+    and #bJoypad::Down
+    tax  ; joypad down bit
+    lda Zp_P1ButtonsHeld_bJoypad
+    and #bJoypad::Up
+    bit Zp_AvatarFlags_bObj
+    .assert bObj::FlipV = bProc::Negative, error
+    bpl @normalGravity
+    @reverseGravity:
+    stx T1  ; joypad look bit
+    sta T0  ; joypad kneel bit
+    bmi @setPose  ; unconditional
+    @normalGravity:
+    sta T1  ; joypad look bit
+    stx T0  ; joypad kneel bit
+    @setPose:
+    ;; Set the avatar's pose based on its state and the joypad.
     lda Zp_AvatarState_bAvatar
     and #bAvatar::LandMask
     beq @standOrRun  ; landing timer is zero
     @landing:
-    lda Zp_P1ButtonsHeld_bJoypad
-    and #bJoypad::Down
+    lda T0  ; joypad kneel bit
     bne @kneeling
     lda #eAvatar::Landing
     bne @setAvatarPose  ; unconditional
@@ -288,11 +305,9 @@ _SetPoseOnGround:
     @standing:
     lda Zp_AvatarHarmTimer_u8
     bne @kneeling
-    lda Zp_P1ButtonsHeld_bJoypad
-    and #bJoypad::Down
+    lda T0  ; joypad kneel bit
     bne @kneeling
-    lda Zp_P1ButtonsHeld_bJoypad
-    and #bJoypad::Up
+    lda T1  ; joypad look bit
     bne @looking
     lda #eAvatar::Standing
     bne @setAvatarPose  ; unconditional

diff --git a/src/platform.asm b/src/platform.asm
@@ -714,11 +714,20 @@ _MovingUp:
     blt _Return
     @topEdgeHit:
     ;; Check bottom edge of platform.
-    lda Ram_PlatformBottom_i16_0_arr, x
-    add #kAvatarBoundingBoxUp  ; TODO: handle reverse gravity
+    bit Zp_AvatarFlags_bObj
+    .assert bObj::FlipV = bProc::Negative, error
+    bpl @normalGravity
+    @reverseGravity:
+    lda #kAvatarBoundingBoxDown + 1
+    .assert kAvatarBoundingBoxDown > 0, error
+    bne @doneBoundingBox  ; unconditional
+    @normalGravity:
+    lda #kAvatarBoundingBoxUp
+    @doneBoundingBox:
+    add Ram_PlatformBottom_i16_0_arr, x
     sta T0  ; platform bottom edge + bbox (lo)
-    lda Ram_PlatformBottom_i16_1_arr, x
-    adc #0
+    lda #0
+    adc Ram_PlatformBottom_i16_1_arr, x
     sta T1  ; platform bottom edge + bbox (hi)
     cmp Zp_AvatarPosY_i16 + 1
     blt _Return
@@ -733,8 +742,17 @@ _MovingUp:
     sta Zp_AvatarPosY_i16 + 0
     lda T1  ; platform bottom edge + bbox (hi)
     sta Zp_AvatarPosY_i16 + 1
-    ;; TODO: if reverse gravity, set Zp_AvatarPlatformIndex_u8
-    jmp _Collided
+    ;; If gravity is reversed, the avatar is now riding this platform.
+    bit Zp_AvatarFlags_bObj
+    .assert bObj::FlipV = bProc::Negative, error
+    bpl _Collided  ; gravity is normal, so avatar isn't riding platform above
+_RidingPlatform:
+    stx Zp_AvatarPlatformIndex_u8
+_Collided:
+    lda Ram_PlatformType_ePlatform_arr, x
+    sta Zp_AvatarCollided_ePlatform
+_Return:
+    rts
 _MovingDown:
     ;; Check bottom edge of platform.
     lda Ram_PlatformBottom_i16_1_arr, x
@@ -766,13 +784,11 @@ _MovingDown:
     sta Zp_AvatarPosY_i16 + 0
     lda T1  ; platform top edge - bbox (hi)
     sta Zp_AvatarPosY_i16 + 1
-    ;; Record that the avatar is now riding this platform.
-    stx Zp_AvatarPlatformIndex_u8  ; TODO: only for normal gravity
-_Collided:
-    lda Ram_PlatformType_ePlatform_arr, x
-    sta Zp_AvatarCollided_ePlatform
-_Return:
-    rts
+    ;; If gravity is normal, the avatar is now riding this platform.
+    bit Zp_AvatarFlags_bObj
+    .assert bObj::FlipV = bProc::Negative, error
+    bpl _RidingPlatform
+    bmi _Collided  ; unconditional
 .ENDPROC
 
 ;;; Determines whether both (1) the bottom of the avatar is below the top of

diff --git a/src/push.asm b/src/push.asm
@@ -398,10 +398,22 @@ _NoHitPassage:
     .assert bObj::FlipV = bProc::Negative, error
     bpl _MovingDown  ; normal gravity; treat no vertical movement as "down"
 _MovingUp:
+    bit Zp_AvatarFlags_bObj
+    .assert bObj::FlipV = bProc::Negative, error
+    bpl @normalGravity
+    @reverseGravity:
+    lda #kAvatarBoundingBoxDown
+    clc  ; subtract an extra 1 below
+    bcc @setBoundingBox  ; unconditional
+    @normalGravity:
+    lda #kAvatarBoundingBoxUp
+    sec  ; perform normal subtraction below
+    @setBoundingBox:
+    sta T3  ; bounding box up
     ;; Calculate the room block row index just above the avatar's head, and
     ;; store it in T2.
     lda Zp_AvatarPosY_i16 + 0
-    sub #kAvatarBoundingBoxUp  ; TODO: handle reverse gravity
+    sbc T3  ; bounding box up
     sta T2
     lda Zp_AvatarPosY_i16 + 1
     sbc #0
@@ -420,16 +432,17 @@ _MovingUp:
     @solid:
     ;; We've hit the ceiling, so set vertical position to just below the
     ;; ceiling we hit.
+    inc T2  ; increment room block row to just below the ceiling
     lda #0
     .repeat 4
-    asl T2  ; room block row index (top of avatar)
+    asl T2  ; room block row index (middle of avatar)
     rol a
     .endrepeat
     tax
-    lda T2
-    add #kBlockHeightPx + kAvatarBoundingBoxUp  ; TODO: handle reverse gravity
+    lda T2  ; bottom of ceiling (lo)
+    adc T3  ; bounding box up (carry is clear from ROL above)
     sta Zp_AvatarPosY_i16 + 0
-    txa
+    txa     ; bottom of ceiling (hi)
     adc #0
     sta Zp_AvatarPosY_i16 + 1
     ;; Indicate that we hit solid terrain.