Differences

This shows you the differences between two versions of the page.

--- software:vectors [2016/06/05 16:57]
ex_writer [Old Screen Address (VBOAL, VBOAH)]
+++ software:vectors [2016/06/12 09:55] (current)
ex_writer [X/Y Check Mask (VBXCHK, VBYCHK)]
@@ Line 67: / Line 67: @@
 ==== X/Y Check Mask (VBXCHK, VBYCHK) ====
-The check mask byte determines whether a limit (i.e., boundary) is attained and how to respond. The limit value is set in vector write routine (e.g., [[system routines:screen handler#vect|VECT]]).
+The check mask byte determines whether a limit (i.e., boundary) is attained and how to respond. Limit values are defined in the object's [[#limit table]] and passed to the object vectoring routines (i.e., [[system routines:screen handler#VECT]] or [[system routines:screen handler#VECTC]]).
 {{:checks_mask.png}}
 ^ Bit ^ Name ^ Label ^ Description ^
-| 0 | Limit Check | | Set to one (1) to enable limit checking. |
+| 0 | Limit Check | VBCLMT | Set to one (1) to enable limit checking. |
-| 1 | Reverse Delta | | Changes the sign of the delta when the limit is reached. This can be used to cause objects to 'bounce' off barriers. |
+| 1 | Reverse Delta | VBCREV | Changes the sign of the delta when the limit is reached. This can be used to cause objects to 'bounce' off barriers. |
-| 3 | Limit Attained | | In contrast to the bounce effect, the system will set the limit attained flag and hold the pattern at the limit position until the user changes the delta. |
+| 3 | Limit Attained | VBCLAT | In contrast to the bounce effect, the system will set the limit attained flag and hold the pattern at the limit position until the user changes the delta. |
@@ Line 82: / Line 82: @@
 VBOAL and VBOAH are maintained by the user if [[system routines:screen handler#VBLANK]] is being used to erase graphics. If so, you must take the absolute screen address calculated by [[system routines:screen handler#VWRITR]] and place it here.
+===== Limit Table =====
+The Limit Table is a four-byte list indicating the boundaries of a vectored pattern:
+^ Byte ^ Name ^ Description ^
+| 1 | X lower limit | The leftmost boundary the pattern may reach |
+| 2 | X upper limit | The rightmost boundary the pattern may reach |
+| 3 | Y lower limit | The topmost boundary the pattern may reach |
+| 4 | Y upper limit | The bottommost edge the pattern may reach |
 ----
 **Reference:** Lance F. Squire,  [[http://www.ballyalley.com/ml/ml_docs/vector%20tutorial/BallyVectorTutorial_(Ver_1.03)(Lance_Squire).pdf|Bally/Astrocade Vector Animation Tutorial]] [PDF].