Routines
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46140: Draw Sprite
Used by the routine at DrawEntityItem.
Draws the sprite of an entity into the screen buffer, which is 24 bytes wide. The sprite data is read by using the stack pointer, and the sprite is drawn by one of the row routines in the table at RowRoutineTable, which is chosen using the width of the sprite and whether it is shifted by the low bits of the column. The addresses of the row routine and the step to the previous row are written into the drawing code before it is entered. If the sprite goes beyond the top of the screen buffer, the rows that are not needed are skipped.
Input
IX The entity
DrawSprite 46140 CALL FindSpriteFrame Find the sprite.
46143 LD A,(IX+22) Read the width byte.
46146 AND %11110000 Use the countdown nibble.
46148 CALL NZ,BuildPatternedSprite Build a patterned copy when that nibble is set.
46151 LD (23770),SP Remember the stack pointer.
46155 LD HL,44519 Use the row-routine table.
46158 LD A,(IX+14) Read the column.
46161 AND %00000110 Use bits 1-2 as the shift.
46163 LD C,A Keep the shift.
46164 LD A,(DE) Read the sprite's width.
46165 LD (46247),A Give the width to the skip loop.
46168 LD B,A Keep the width.
46169 JR Z,DrawSprite_Index A shifted sprite uses the next routine and one more byte.
46171 ADD A,4
46173 INC B
DrawSprite_Index 46174 ADD A,A Double the width to make a table index.
46175 CALL AddToAddress Look the row routine up.
46178 LD A,(HL) Read the routine's address.
46179 INC HL
46180 LD H,(HL)
46181 LD L,A
46182 LD (46266),HL Give the routine and the row step to the drawers.
46185 LD (46270),HL
46188 LD (46305),HL
46191 LD (46388),HL
46194 LD (46393),HL
46197 INC DE Move on to the sprite data.
46198 LD A,B The step back across a row is the width plus 23.
46199 ADD A,23
46201 LD (46384),A
46204 NEG The other step is the opposite of that width.
46206 LD (46300),A
46209 LD L,(IX+24) Fetch the screen address.
46212 LD H,(IX+25)
46215 EX DE,HL Keep the sprite address aside.
46216 LD A,(HL) Read how many rows the sprite has.
46217 LD B,A
46218 EX AF,AF' Remember that count.
46219 LD A,(IX+15) The first row to draw is one past the entity's row.
46222 INC A
46223 INC HL Read the sprite through the stack.
46224 LD SP,HL
46225 CP B Clip the sprite when its rows end above the view.
46226 JP NC,DrawSprite_Clip
46229 LD B,A The row count is that first row.
46230 EX AF,AF' Bring the sprite's row count back.
46231 JP DrawSprite_2 Draw the sprite.
DrawSprite_Clip 46234 SUB 128 A count below 128 is drawn whole.
46236 JP C,DrawSprite_2
46239 JP Z,DrawSprite_2 A count of exactly 128 is drawn whole.
46242 LD B,A The rows above the view are the excess.
46243 EX AF,AF' Bring the sprite's row count back.
46244 SUB B Drop the rows that are off the view.
46245 EX AF,AF'
DrawSprite_0 46246 LD B,0 Skip one row of the sprite.
DrawSprite_1 46248 POP HL Skip the bytes of that row.
46249 DJNZ DrawSprite_1
46251 DEC A Repeat for the remaining rows above the view.
46252 JR NZ,DrawSprite_0
46254 EX AF,AF' Bring the rows that are in view back.
46255 LD B,A Use that as the row count.
46256 EX AF,AF'
DrawSprite_2 46257 LD A,C Read the shift.
46258 AND A An unshifted sprite is drawn directly.
46259 JR Z,DrawSprite_4
46261 ADD A,248 A shifted sprite uses the page selected by the shift.
46263 LD H,A
46264 LD A,(DE)
DrawSprite_3 46265 JP DrawSprite_3 Draw the shifted rows. The target is patched.
DrawSprite_4 46268 EX DE,HL Put the screen address in HL.
DrawSprite_5 46269 JP DrawSprite_5 Draw the unshifted rows. The target is patched.
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