.DrawSpriteImage LDA #%00000001 ; Set S to use as the attribute for each of the sprites STA S ; in the image, so each sprite is set as follows: ; ; * Bits 0-1 = sprite palette 1 ; * Bit 5 clear = show in front of background ; * Bit 6 clear = do not flip horizontally ; * Bit 7 clear = do not flip vertically LDA XC ; Set SC = XC * 8 + X ASL A ; = XC * 8 + 6 ASL A ; ASL A ; So SC is the pixel x-coordinate of the top-left corner ADC #0 ; of the image we want to draw, as each text character STA SC ; in XC is 8 pixels wide and X contains the x-coordinate TXA ; within the character block ADC SC STA SC LDA YC ; Set SC+1 = YC * 8 + 6 + Y ASL A ; = YC * 8 + 6 + 6 ASL A ; ASL A ; So SC+1 is the pixel y-coordinate of the top-left ADC #6+YPAL ; corner of the image we want to draw, as each text row STA SC+1 ; in YC is 8 pixels high and Y contains the y-coordinate TYA ; within the character block ADC SC+1 STA SC+1 LDA K+3 ; Set Y = K+3 * 4 ASL A ; ASL A ; So Y contains the offset of the first free sprite's TAY ; four-byte block in the sprite buffer, as each sprite ; consists of four bytes, so this is now the offset ; within the sprite buffer of the first sprite we can ; use to build the sprite image LDA K+2 ; Set A to the pattern number of the first tile in K+2 LDX K+1 ; Set T = K+1 to use as a counter for each row in the STX T ; image .drsi1 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure ; the PPU to use nametable 0 and pattern table 0 LDX SC ; Set SC2 to the pixel x-coordinate for the start of STX SC2 ; each row, so we can use it to move along the row as we ; draw the sprite image LDX K ; Set X to the number of tiles in each row of the image ; (in K), so we can use it as a counter as we move along ; the row .drsi2 LDA K+2 ; Set the pattern for sprite Y to K+2, which is the STA pattSprite0,Y ; pattern number in the PPU's pattern table to use for ; this part of the image LDA S ; Set the attributes for sprite Y to S, which we set STA attrSprite0,Y ; above as follows: ; ; * Bits 0-1 = sprite palette 1 ; * Bit 5 clear = show in front of background ; * Bit 6 clear = do not flip horizontally ; * Bit 7 clear = do not flip vertically LDA SC2 ; Set the x-coordinate for sprite Y to SC2 STA xSprite0,Y CLC ; Set SC2 = SC2 + 8 ADC #8 ; STA SC2 ; So SC2 contains the x-coordinate of the next tile ; along the row LDA SC+1 ; Set the y-coordinate for sprite Y to SC+1 STA ySprite0,Y TYA ; Add 4 to the sprite number in Y, to move on to the CLC ; next sprite in the sprite buffer (as each sprite ADC #4 ; consists of four bytes of data) BCS drsi3 ; If the addition overflowed, then we have reached the ; end of the sprite buffer, so jump to drsi3 to return ; from the subroutine, as we have run out of sprites TAY ; Otherwise set Y to the offset of the next sprite in ; the sprite buffer INC K+2 ; Increment the tile counter in K+2 to point to the next ; pattern DEX ; Decrement the tile counter in X as we have just drawn ; a tile BNE drsi2 ; If X is non-zero then we still have more tiles to ; draw on the current row, so jump back to drsi2 to draw ; the next one LDA SC+1 ; Otherwise we have reached the end of this row, so add ADC #8 ; 8 to SC+1 to move the y-coordinate down to the next STA SC+1 ; tile row (as each tile row is 8 pixels high) DEC T ; Decrement the number of rows in T as we just finished ; drawing a row BNE drsi1 ; Loop back to drsi1 until we have drawn all the rows in ; the image .drsi3 RTS ; Return from the subroutineName: DrawSpriteImage [Show more] Type: Subroutine Category: Drawing sprites Summary: Draw an image out of sprites using patterns in sequential tiles in the pattern buffer Deep dive: Sprite usage in NES EliteContext: See this subroutine in context in the source code References: This subroutine is called as follows: * DrawSpriteImage_b6 calls DrawSpriteImage * DrawMedallion calls via DrawSpriteImage+2
Arguments: K The number of columns in the image (i.e. the number of tiles in each row of the image) K+1 The number of tile rows in the image K+2 The pattern number of the start of the image pattern data in the pattern table K+3 Number of the first free sprite in the sprite buffer, where we can build the sprites to make up the image XC The text column of the top-left corner of the image YC The text row of the top-left corner of the image X The pixel x-coordinate of the top-left corner of the image within the text block at (XC, YC) Y The pixel y-coordinate of the top-left corner of the image within the text block at (XC, YC)
Other entry points: DrawSpriteImage+2 Set the attributes for the sprites in the image to A
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Macro SETUP_PPU_FOR_ICON_BAR (category: PPU)
If the PPU has started drawing the icon bar, configure the PPU to use nametable 0 and pattern table 0
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Configuration variable YPAL = 6 AND _PAL
A margin of 6 pixels that is applied to a number of y-coordinates for the PAL version only (as the PAL version has a taller screen than NTSC)
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Variable attrSprite0 in workspace Sprite buffer
Attributes for sprite 0
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Label drsi1 is local to this routine
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Label drsi2 is local to this routine
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Label drsi3 is local to this routine
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Variable pattSprite0 in workspace Sprite buffer
Pattern number for sprite 0
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Variable xSprite0 in workspace Sprite buffer
Screen x-coordinate for sprite 0
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Variable ySprite0 in workspace Sprite buffer
Screen y-coordinate for sprite 0