Routines
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51432: Scroll View Left
Used by the routine at ScrollView.
Scrolls the view to the left when the player has moved towards the right of the view. The buffer is shifted with one of the routines in the table at ShiftLeftTable, the view is moved with AdjustViewOrigin and the objects that have come into view are drawn using DrawRightStrip.
Input
IX The player entity
Check whether the player is near enough to the right of the view for the view to scroll to the left. If it is not, stop scrolling.
ScrollViewLeft 51432 LD A,(23792) Fetch the scroll position along the view and keep it in C.
51435 LD C,A
51436 LD A,(IX+14) Fetch the column of the player on the screen and keep it in D.
51439 LD D,A
51440 CP 104 Compare it with 104.
51442 LD L,252 Set the bits of the view flags to keep, to clear the scroll bits.
51444 JP C,UpdateViewFlags Jump to UpdateViewFlags if the player is not near the right of the view.
Choose the speed to scroll at, which is two pixels a frame when the player is near the edge of the view and one pixel a frame otherwise.
51447 LD E,2 Set the speed to two pixels.
51449 LD A,(23782) Fetch the view flags.
51452 AND %00000011 Keep the scroll left bits.
51454 CP 2 Jump to ScrollViewLeft_CheckPhase if the view is not already scrolling at two pixels.
51456 JR NZ,ScrollViewLeft_CheckPhase
51458 LD A,D Fetch the column of the player.
51459 CP 116 Jump to ScrollViewLeft_OnePixel to slow down to one pixel if the player is not as far across as that.
51461 JR C,ScrollViewLeft_OnePixel
51463 JR ScrollViewLeft_Scroll Keep the speed at two pixels.
ScrollViewLeft_CheckPhase 51465 LD A,C Fetch the scroll position.
51466 AND %00000011 Keep the low two bits.
51468 JR NZ,ScrollViewLeft_OnePixel Slow down to one pixel if it is part way through a pixel step.
51470 LD A,D Fetch the column of the player.
51471 CP 128 Jump to ScrollViewLeft_Scroll to keep the speed at two pixels if the player is that far across.
51473 JR NC,ScrollViewLeft_Scroll
ScrollViewLeft_OnePixel 51475 DEC E Slow down to one pixel.
ScrollViewLeft_Scroll 51476 PUSH DE Save the speed.
When the view has scrolled by another sixteen pixels, draw the objects that have come into view along the right edge of the buffer.
51477 LD HL,58833 Point HL at the right of the first row of the buffer.
51480 LD (23739),HL Store it as the place to draw to.
51483 LD HL,49377 Point HL at the routine that draws the objects in the right strip.
51486 LD A,C Fetch the scroll position.
51487 AND %00001111 Keep the low four bits.
51489 CALL Z,DrawLevelObjects Draw the objects of the level in the strip if it is a multiple of sixteen.
51492 POP DE Restore the speed.
Move the view along by the speed and note it in the view flags.
51493 CALL AdjustViewOrigin Move the origin of the view.
51496 LD A,E Fetch the speed.
51497 SRL A Halve it.
51499 LD E,A Keep it in E.
51500 INC A Add one, to make the scroll left value of the flags.
51501 LD B,A Copy it into B.
51502 LD A,(23782) Fetch the view flags.
51505 AND %11111100 Clear the scroll left bits.
51507 OR B Set the new scroll left value.
51508 LD (23782),A Store the view flags.
51511 LD HL,51651 Point HL at the table of routines that shift the buffer to the left.
51514 JP JumpViaTable_Index Shift the buffer.
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