Routines
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6F10: Calculate Screen Address
Used by the routines at MenuWriteText, HandlerCup, DisplayBestTime, DisplayPlaceName, PrintStringColour, FlashPlayerMarker, DisplayNightDriver, PlotPixels, PrepareOldSprite and PrepareActorSprite.
Converts pixel co-ordinates into the matching address in the screen buffer.
Input
HL Pixel co-ordinates (H is the Y position, counting down from the top of the screen, and L is the X position)
Output
HL Screen buffer address
ScreenAddress 6F10 LD A,L A=L.
6F11 RRCA A=A / 08.
6F12 RRCA
6F13 RRCA
6F14 AND %00011111 Keep only bits 0-4.
6F16 LD L,A L=A.
6F17 LD A,H A=H.
6F18 RLCA A=A * 04.
6F19 RLCA
6F1A AND %11100000 Keep only bits 5-7.
6F1C OR L Set the bits from L.
6F1D LD L,A L=A.
6F1E LD A,H A=H.
6F1F AND %00000111 Keep only bits 0-2.
6F21 EX AF,AF' Switch to the shadow AF register.
6F22 LD A,H A=H.
6F23 RRCA A=A / 08.
6F24 RRCA
6F25 RRCA
6F26 AND %00011000 Keep only bits 3-4.
6F28 OR %01000000 Set bit 6.
6F2A LD H,A H=A.
6F2B EX AF,AF' Switch to the shadow AF register.
6F2C OR H Set the bits from H.
6F2D LD H,A H=A.
6F2E RET Return.
View the equivalent code in;
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