Routines
Prev: ED2E Up: Map Next: EDB4
ED8A: Check Rock Formation Contact
Used by the routine at Check_Object_Contact.
Checks whether an object touches the rock formation (see Handle_Rock_Formation). It is used by Check_Object_Contact in place of the usual test when the obstacle is of the type 88.
The formation is a triangle with its point at the bottom, which is centred on the x position 80. The half width of the triangle at the height of the object is 9A less the y position of the object, divided by four (the half width is larger when the object is higher) and then 08 is added. An object touches the formation when it is not below 90 and its distance from the centre is less than that.
The result has bits 0 and 2 set when the object touches the formation, and bit 7 as well when the object is on the right of the centre. The object is never standing on the formation.
Input
IX Object record
Output
C Contact result (see Check_Object_Contact)
Check_Rock_Formation_Contact ED8A LD C,$00 Clear the contact result.
ED8C LD B,$01 B=01.
ED8E LD A,(IX+$03) Fetch the y position of the object.
ED91 CP $90 Return if the object is 90 or more pixels down, as it is below the formation.
ED93 RET NC
ED94 NEG Negate the y position.
ED96 SUB $66 Subtract 66 which gives 9A less the y position.
ED98 SRL A Divide the result by four.
ED9A SRL A
ED9C ADD A,$08 Add 08.
ED9E LD D,A Store the half width in D.
ED9F LD A,$80 Set the centre of the formation, 80.
EDA1 SUB (IX+$01) Jump to Check_Rock_Formation_Contact_Test_Width if the object is on the left of the centre.
EDA4 JP P,Check_Rock_Formation_Contact_Test_Width
EDA7 NEG Make the distance positive.
EDA9 SET 7,C Set bit 7 of the result, as the object is on the right.
Check_Rock_Formation_Contact_Test_Width EDAB CP D Jump to Check_Object_Contact_None if the distance is the half width or more, as the objects do not touch.
EDAC JP NC,Check_Object_Contact_None
EDAF SET 0,C Set bit 0 of the result, as the object is outside the middle.
EDB1 SET 2,C Set bit 2 of the result, as the objects touch.
EDB3 RET Return.
Prev: ED2E Up: Map Next: EDB4