Routines
Prev: A6FD Up: Map Next: A779
A6FF: Handler: Run Script
Used by the routines at Handler_GameEvents, Handler_ScenicEvents, Handler_DispatchVerb and ChangeRoom.
Executes the bytecode at IX.
Each instruction is a condition from JumpTable_ScriptConditions followed by an action from JumpTable_ScriptActions. A condition that fails skips its action.
FE selects OR for the next condition and FF selects AND.
FF ends the instruction and starts another one.
Input
IX Pointer to the script bytecode
Preserve the caller's registers for Action_EndScript.
Handler_RunScript A6FF PUSH HL Stash HL, DE and BC on the stack.
A700 PUSH DE
A701 PUSH BC
Begin a new instruction: clear the condition mask and reset the operator to AND.
RunScript_NewInstruction A702 LD HL,$A6FD HL=ScriptConditionMask.
A705 LD (HL),$40 Start the condition mask at 40 (only the zero flag set, meaning the conditions hold).
A707 INC HL Move HL on to the condition operator.
A708 LD (HL),$FF Start with the AND operator (FF).
Dispatch the condition opcode at *IX through JumpTable_ScriptConditions.
RunScript_DispatchCondition A70A LD E,(IX+$00) Fetch the condition opcode from *IX+00 into E.
A70D PUSH IX Stash IX on the stack.
A70F LD IX,$A785 IX=JumpTable_ScriptConditions.
A713 CALL GetTableEntry Call GetTableEntry to fetch the condition routine address into HL.
A716 POP IX Restore IX from the stack.
A718 JP (HL) Jump to the condition routine held in HL.
Conditions of different lengths jump into this run of INC IX at different points, so each entry point skips the right number of bytes.
RunScript_SkipCondition_FourBytes A719 INC IX Move IX past the four bytes of this condition.
This entry point is used by the routines at Condition_ItemLocationEquals, Condition_ItemLocationDiffers, Condition_GroupItemEquals, Condition_GroupItemDiffers, Condition_RoomPairMatches and Condition_RoomPairDiffers.
RunScript_SkipCondition_ThreeBytes A71B INC IX Move IX past the three bytes of this condition.
This entry point is used by the routines at Condition_ItemIsPresent, Condition_ItemIsAbsent, Condition_ItemIsCarried, Condition_ItemIsNotCarried, Condition_ItemIsHere, Condition_InRoom, Condition_NotInRoom, Condition_FlagIsSet, Condition_FlagIsClear, Condition_InventoryCountEquals, Condition_InventoryCountDiffers, Condition_MarkedRoomEquals, Condition_MarkedRoomDiffers, Condition_PhraseMatches, Condition_PhraseDoesNotMatch, Condition_ParserSucceeds, Condition_ParserFails, Condition_ParserResultEquals, Condition_ParserResultDiffers, Condition_CanTakeItem, Condition_CannotTakeItem, Condition_IsCarryingForDrop and Condition_IsNotCarryingForDrop.
RunScript_SkipCondition_TwoBytes A71D INC IX Move IX past the two bytes of this condition.
This entry point is used by the routine at Condition_AlwaysSucceeds.
RunScript_SkipCondition_OneByte A71F INC IX Move IX past the one byte of this condition.
Combine this condition's result with the running mask using AND or OR.
A721 PUSH AF Copy the result flags of this condition into C (bit 6 is its zero flag).
A722 POP BC
A723 LD A,($A6FE) See whether the current operator in *ScriptConditionOperator is OR (FE).
A726 CP $FE
A728 LD A,($A6FD) Fetch the running condition mask from *ScriptConditionMask.
A72B JR NZ,RunScript_CombineWithAnd Jump to RunScript_CombineWithAnd if *ScriptConditionOperator is not equal to FE.
A72D OR C The script operator is "or", so this check passes if either condition held (OR C).
A72E JR RunScript_StoreConditionMask Jump to RunScript_StoreConditionMask.
RunScript_CombineWithAnd A730 AND C Otherwise both conditions must hold (AND C).
RunScript_StoreConditionMask A731 LD ($A6FD),A Store the combined condition result at ScriptConditionMask.
After the condition, either chain another with AND/OR, or dispatch the action.
A734 LD A,(IX+$00) Fetch the next script byte from *IX+00.
A737 CP $FE Jump to RunScript_DispatchAction if it is an action opcode (less than FE).
A739 JR C,RunScript_DispatchAction
A73B LD ($A6FE),A Store the new AND/OR operator at ScriptConditionOperator.
A73E INC IX Move IX on to the next script byte.
A740 JR RunScript_DispatchCondition Jump to RunScript_DispatchCondition.
Advance past a chained action separator, then dispatch the action opcode.
RunScript_NextAction A742 INC IX Move IX on to the action opcode.
RunScript_DispatchAction A744 LD E,(IX+$00) Fetch the action opcode from *IX+00 into E.
A747 PUSH IX Stash IX on the stack.
A749 LD IX,$A7C1 IX=JumpTable_ScriptActions.
A74D CALL GetTableEntry Call GetTableEntry to fetch the action routine address into HL.
A750 POP IX Restore IX from the stack.
A752 LD A,($A6FD) Pass the condition mask to the action as its flags, so the zero flag says whether the conditions hold.
A755 LD C,A
A756 PUSH BC
A757 POP AF
A758 JP (HL) Jump to the action routine held in HL.
Actions of different lengths jump into this run of INC IX at different points, so each entry point skips the right number of bytes.
RunScript_SkipAction_FourBytes A759 INC IX Move IX past the four bytes of this action.
This entry point is used by the routines at Action_JumpToScript, Action_CallScript, Action_PrintMessage, Action_PrintMessageAndNewline, Action_PlaceItem, Action_TransformItem, Action_SetTurnCounter and Action_WriteSavedByte.
RunScript_SkipAction_ThreeBytes A75B INC IX Move IX past the three bytes of this action.
This entry point is used by the routines at Action_BringItemHere, Action_DestroyItem, Handler_PickUpItem, Handler_DropItem, Action_GoToRoom, Action_SetFlag, Action_ClearFlag, Action_AddToScore, Action_Pause, Action_MarkScenicEvent, Action_SetEventFlag, Action_ClearEventFlag, Action_StartTurnEvent, Action_StopTurnEvent, Action_MovePlayer and Action_SetCarryingLimit.
RunScript_SkipAction_TwoBytes A75D INC IX Move IX past the two bytes of this action.
This entry point is used by the routines at Action_ReturnFromScript, Action_EndScript, Action_IncrementInventory, Action_DecrementInventory, Action_LoadGame, Action_SaveGame, Action_DescribeRoom, Action_ListInventory, Action_OfferSave and Action_PrintScore.
RunScript_SkipAction_OneByte A75F INC IX Move IX past the one byte of this action.
This entry point is used by the routines at Action_JumpToScript, Action_CallScript and Action_ReturnFromScript.
Decide whether another action follows, or whether to start a new instruction.
RunScript_AfterAction A761 LD A,(IX+$00) Fetch the next script byte from *IX+00.
A764 CP $FF Jump to RunScript_NextAction if it is the chained-action marker FF.
A766 JR Z,RunScript_NextAction
A768 JR RunScript_NewInstruction Jump to RunScript_NewInstruction.
This entry point is used by the routines at Condition_ItemIsAbsent, Condition_ItemIsNotCarried, Condition_NotInRoom, Condition_ItemLocationDiffers, Condition_FlagIsSet, Condition_GroupItemDiffers, Condition_InventoryCountDiffers, Condition_MarkedRoomDiffers, Condition_PhraseDoesNotMatch, Condition_ParserSucceeds, Condition_ParserFails, Condition_ParserResultDiffers, Condition_RoomPairDiffers, Condition_CannotTakeItem and Condition_IsNotCarryingForDrop.
Invert a condition result: succeed when the tested flag was clear.
RunScript_InvertConditionResult A76A JR NZ,RunScript_ConditionHolds Jump to RunScript_ConditionHolds if the zero flag is not set.
A76C LD A,$01 Load 01 so the following AND A clears the zero flag.
A76E AND A Clear the zero flag; the inverted condition does not hold.
A76F RET Return.
RunScript_ConditionHolds A770 XOR A Clear A and set the zero flag; the inverted condition holds.
A771 RET Return.
This entry point is used by the routines at Condition_ItemIsPresent, Condition_ItemIsAbsent, Condition_ItemIsCarried, Condition_ItemIsNotCarried, Condition_ItemIsHere, Condition_ItemLocationEquals, Condition_ItemLocationDiffers, Condition_CanTakeItem, Condition_CannotTakeItem, Condition_IsCarryingForDrop, Condition_IsNotCarryingForDrop, Action_PlaceItem, Action_BringItemHere, Action_TransformItem, Action_DestroyItem, Handler_PickUpItem, Handler_DropItem and Action_MarkScenicEvent.
When the operand is FF substitute the matched item ID from ScriptMatchedItem.
RunScript_ResolveMatchedItem A772 CP $FF Return if the operand is not the matched-item sentinel FF.
A774 RET NZ
A775 LD A,($A805) Fetch the matched item ID from *ScriptMatchedItem.
A778 RET Return.
Prev: A6FD Up: Map Next: A779