; ***************************************************************************** ; ***************************************************************************** ; ; Draw Sprites ; ; ***************************************************************************** ; ***************************************************************************** ; ***************************************************************************** ; ; Draw Sprite. Sprite Data ^ BX, Scanline Range in CL..CH ; ; ***************************************************************************** _ScanLo:db 0 ; Start & End displayed scanlines. _ScanHi:db 0 _SLCount:db 0 ; scanline counter _SLCtrl:db 0 ; control byte (from byte 2 of sprites) _BaseAddr:dw 0 ; base address of sprites _SVector:dw 0 ; sprite drawing routine DrawSprite: push ax,bx,cx mov al,[bx] ; check range of sprite coords cmp al,0 ; y must be > 0 and <= 240 to draw jz _DSExit2 cmp al,240 jbe _DSDraw _DSExit2: jmp _DSExit _DSDraw: mov [_ScanLo],cl ; save scan line boundaries mov [_ScanHi],ch mov al,1[bx] ; get pattern # in ax xor ah,ah shl ax,4 ; ax = pattern# * 16 test byte [PPUCtrl1],8 ; adjust if using other pattern bank jz _DS1 ; for sprites add ax,01000h _DS1: mov [_BaseAddr],ax ; save the base address add ax,VROM ; now points into VROM mov di,ax ; di points to the sprite patterns now. mov al,2[bx] ; get the attribute bits and al,3 shl al,2 ; x by 4 xor ah,ah mov si,NESPalette+16 ; si point to base. add si,ax mov cl,[si] ; get the colours. mov ch,1[si] mov dl,2[si] mov dh,3[si] and cx,3F3Fh add cx,4040h and dx,3F3Fh add dx,4040h mov al,2[bx] ; get the control bit mov [_SLCtrl],al mov ah,[bx] ; ah = y coordinate mov al,3[bx] ; al = x coordinate ; ; now cl/ch/dl/dh contain the colours, (al,ah) position ; and si points to the bit data ; mov es,[VSSegment] mov byte [_SlCount],8 ; number of write lines mov word [_SVector],SpriteBitLine test byte [PPUCtrl1],32 ; 8 x 16 sprites ? jz _DS2 mov byte [_SlCount],16 _DS2: test byte [_SLCtrl],32 ; behind background jz _DS4 mov word [_SVector],SpriteBehindLine _DS4: test byte [_SLCtrl],128 ; vertical flip jz DoLine add di,7 ; start from the bottom. DoLine: call SPGetLine ; get the screen line address into bx cmp bx,0 ; if zero,don't draw on this line jz DoNextLine cmp ah,[_ScanLo] ; if < Lo Scan,don't draw it. jb DoNextLine cmp ah,[_ScanHi] ; if > Hi Scan,finish this sprite jae _DSExit push ax ; save coordinates xor ah,ah ; ax = x position add bx,ax ; bx = where the sprite goes mov al,[di] ; get the bit patterns out. mov ah,8[di] test byte [_SLCtrl],64 ; x flipping ???? jz NoXFlip call XReverse NoXFlip: push ds ; draw the bitmap onto the screen push es pop ds call [cs:_SVector] pop ds,ax ; restore coordinates DoNextLine: inc ah ; next vertical scan line inc di ; next byte from pattern table test byte [_SLCtrl],128 ; vertically flipped ??? jz _DS3 dec di ; prev byte from pattern table dec di _DS3: ; if its an 8x16 sprite cmp byte [_SlCount],9 ; change the pattern table jne _DS5 ; to the other one mov di,[_BaseAddr] xor di,16 add di,VROM _DS5: dec byte [_SlCount] jnz DoLine _DSExit: pop cx,bx,ax ret SPGetLine: ; get video line in bx for line ah #if LineSize=320 push cx mov bl,ah ; bl = line # xor bh,bh add bx,bx ; bx = line # * 2 add bx,[LineTable] mov cx,[bx] ; get the line address mov bx,cx pop cx ret #else mov bh,ah xor bl,bl sub bh,8 ret #endif XReverse: ; reverse al & ah push bx mov bl,al xor bh,bh mov al,Reverse[bx] mov bl,ah mov ah,Reverse[bx] pop bx ret ; ; this is the same as Bitline, except it uses the SprBlastVec ; table rather than the BitBlastVec table ; ; the main difference is that the 0 graphic isn't written out. ; SpriteBitLine: ; here ah = h7-h4 h3-h0 al = l7-l4 l3-l0 ror al,4 ; now ah = h7-h4 h3-h0 al = l3-l0 l7-l4 ror ax,4 ; now ah = l7-l4 h7-h4 al = h3-h0 l3-l0 ror ah,4 ; now ah = h7-h4 l7-l4 al = h3-h0 l3-l0 push ax ; save al for later,we're doing ah first mov al,ah ; si = 0 al xor ah,ah add ax,ax mov si,ax call SprBlastVec[cs:si] ; call the writing vector add bx,4 ; next nibl pop ax xor ah,ah add ax,ax mov si,ax call SprBlastVec[cs:si] add bx,LineSize-4 ; next line down ret SpriteBehindLine: push cx,dx mov cl,8 ; bits to write counter SBL1: mov ch,[bx] ; look at the screen and ch,63 cmp ch,cs:[NESPalette] jne SBL2 ; try the next one. test ah,128 jnz SBLBit1Set test al,128 ; ah & 128 = 0 now jz SBL2 mov ch,1[cs:si] jmp SBLW SBLBit1Set: test al,128 ; ah & 128 = 1 now mov ch,2[cs:si] jz SBLW mov ch,3[cs:si] SBLW: and ch,63 add ch,64 mov [bx],ch SBL2: shl ax,1 ; shift ah & al right one inc bx ; next pixel dec cl jnz SBL1 add bx,LineSize-8 pop dx,cx ret