Routines
Prev: 60718 Up: Map Next: 60852
60810: 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 136.
The formation is a triangle with its point at the bottom, which is centred on the x position 128. The half width of the triangle at the height of the object is 154 less the y position of the object, divided by four (the half width is larger when the object is higher) and then 8 is added. An object touches the formation when it is not below 144 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 60810 LD C,0 Clear the contact result.
60812 LD B,1 B=1.
60814 LD A,(IX+3) Fetch the y position of the object.
60817 CP 144 Return if the object is 144 or more pixels down, as it is below the formation.
60819 RET NC
60820 NEG Negate the y position.
60822 SUB 102 Subtract 102 which gives 154 less the y position.
60824 SRL A Divide the result by four.
60826 SRL A
60828 ADD A,8 Add 8.
60830 LD D,A Store the half width in D.
60831 LD A,128 Set the centre of the formation, 128.
60833 SUB (IX+1) Jump to Check_Rock_Formation_Contact_Test_Width if the object is on the left of the centre.
60836 JP P,Check_Rock_Formation_Contact_Test_Width
60839 NEG Make the distance positive.
60841 SET 7,C Set bit 7 of the result, as the object is on the right.
Check_Rock_Formation_Contact_Test_Width 60843 CP D Jump to Check_Object_Contact_None if the distance is the half width or more, as the objects do not touch.
60844 JP NC,Check_Object_Contact_None
60847 SET 0,C Set bit 0 of the result, as the object is outside the middle.
60849 SET 2,C Set bit 2 of the result, as the objects touch.
60851 RET Return.
Prev: 60718 Up: Map Next: 60852