; ***************************************************************************** ; ***************************************************************************** ; ; Redraw the whole screen ; ; ***************************************************************************** ; ***************************************************************************** _ScrCount:dw 0 Screen: push es,ax,bx,cx,dx,si,di,bp mov ax,[_ScrCount] ; redraw screen cmp ax,0 ; only if screen count is zero. jnz _NoPaint test byte [PPUCtrl2],8 jz _NoRScrn push cx ; Draw the background call RedrawScreen pop cx _NoRScrn: test byte [PPUCtrl2],16 ; Check if sprites being drawn jz _NoSprites mov bx,SpriteRAM+252 mov al,64 _Sprites: call DrawSprite sub bx,4 dec al jnz _Sprites _NoSprites: call ScreenCopy _NoPaint: pop bp,di,si,dx,cx,bx,ax,es ret ; ***************************************************************************** ; ; Redraw screen ; ; From ScanLine cl to Scanline ch ! ; ; To be implemented - horizontal scrolling. ; ; ***************************************************************************** RedrawScreen: mov dl,[PPUVScroll] ; dx = top line of screen,real coords xor dh,dh push cx ; dx = start line for redraw xor ch,ch add dx,cx pop cx clc sub ch,cl ; and do ch lines inc ch ; ; At this point. dx is the first real screen line we want to write ; if you think of the screen as being 512 x 480 we must write ; the line in dx at screen scanline dl ; ; because they are normally done in chunks of 8, we need to make ; the current scan line (cl) up to the 8th line,so we can work ; in whole scan lines from there on. ; test dx,7 ; are we at a border anyway jz NoMakeToEdge call MakeBufferForDx ; make tile buffer for the line ; that contains Dx. ; ; we need to start part way through the tile buffer - ; so we calculate the start position as 320 * (dl & 7) ; mov ax,dx ; ax = dx & 7 and ax,7 shl ax,6 ; ax = bx = * 64 mov bx,ax shl ax,2 ; ax = 256* bx = 64* add ax,bx ; ax = 320* mov bx,TileBuffer add bx,ax ; bx is where we start drawing from PadToStart: call LineCopy ; copy bx to scanline cl add bx,320 ; do the next tilebuffer line inc cl ; next scan line dec ch ; decrement lines to copy jz RSExit inc dx ; keep going until we've reached test dx,7 ; a tile border. jnz PadToStart ; ; at this point , we can write in whole scan blocks. ; NoMakeToEdge: call MakeBufferForDx ; make a buffer for the current line mov bx,TileBuffer DrawScreen: call LineCopy ; copy bx to scanline cl add bx,320 ; do the next tilebuffer line inc cl ; and the next scanline dec ch ; decrement lines to copy jz RSExit ; not finished yet inc dx ; next scroll line test dx,7 jnz DrawScreen ; go back and do another jmp NoMakeToEdge RSExit: ret ; ***************************************************************************** ; ; Make the TileBuffer for the tile line CONTAINING DX ; DX = 0..479 and is a pointer into the 50 tile lines that ; make up the name table map. ; ; ***************************************************************************** MakeBufferForDX: push ax,bx,cx,dx,si,di _MDF1: cmp dx,480 ; first make sure jb _MDFRange ; that dx isn't >= 480 sub dx,480 ; it could be if you really scroll ! jmp _MDF1 ; ; first we have to get the home table, then if we are on the ; bottom half of the virtual screen, we use its vertical pair ; got by toggling 800h bit ; _MDFRange: mov bl,[PPUCtrl1] ; get the address of the name table and bl,3 ; that is the 'home' table xor bh,bh shl bx,10 ; bx = 000,400,800,C00 add bx,02000h ; bx = 2000,2400,2800,2C00 shr dx,3 ; convert 0..399 into 0..49 cmp dx,30 ; if line < 25 then use this one. jl _MDF2 xor bx,0800h ; else use its vertical twin. sub dx,30 ; dx is now an vertical offset. _MDF2: mov cl,dl ; save the tile vertical # in cl shl dx,5 ; dx = dx * 32 mov al,[PPUHScroll] ; horizontal scrolling cmp al,0 jne _MDFHscroll ; ; only if there is no horizontal scrolling. ; call MapPPUAddress ; convert into a real address add bx,PPURam ; bx now ^ tile table base add dx,bx ; dx ^ tile line mov di,dx ; di = the tiles add bx,03C0h ; si = table base + 3C0h mov si,bx ; e.g. the attribute table mov dl,cl ; dl = vertical tile position mov dh,0 ; dh = horizontal tile position mov bx,TileBuffer ; bx = the buffer. mov ch,32 ; do 32 characters. call RenderLine ; Render that line into the tile buffer _MDFExit: pop di,si,dx,cx,bx,ax ret ; ; Horizontal Scrolling ; _MDFHScroll: push bx,cx,dx ; save page addr & tile vertical call MapPPUAddress ; convert into a real address add bx,PPURam ; bx now ^ tile table base add dx,bx ; dx ^ tile line mov di,dx ; di = the tiles add bx,03C0h ; si = table base + 3C0h mov si,bx ; e.g. the attribute table mov al,[PPUHScroll] ; al = # tiles to scroll shr al,3 ; = hscroll / 8 xor ah,ah ; add it to the table base. add di,ax mov dl,cl ; dl = vertical tile position mov dh,al ; dh = horizontal tile position mov bx,TileBuffer ; bx = the buffer. mov ch,32 ; do 32 characters - scroll# sub ch,al call RenderLine ; Render that line into the tile buffer pop dx,cx,bx ; restore tilevert & page xor bx,0400h ; make bx point to the other page call MapPPUAddress ; points to page in RAM add bx,PPURam add dx,bx mov di,dx ; di = the tiles add bx,03C0h ; si = table base + 3C0h mov si,bx ; e.g. the attribute table mov ah,[PPUHScroll] ; al = 32 - HScroll/8 shr ah,3 mov al,32 sub al,ah xor ah,ah ; ax = al * 32 shl ax,3 mov dl,cl ; dl = vertical tile position mov dh,0 ; dh = horizontal tile position mov bx,TileBuffer ; bx = the buffer. add bx,ax mov ch,[PPUHScroll] ; do scroll#/8 + 1 characters shr ch,3 inc ch call RenderLine ; Render that line into the tile buffer jmp _MDFExit ; ***************************************************************************** ; ; Copy Data at DS:BX (256 pixels) out to Scan Line Cl ; adjust for horizontal scrolling ; ; ***************************************************************************** LineCopy: push es,si,di,cx,bx,ax mov al,[PPUHScroll] ; add the scrolling offset and al,7 xor ah,ah add bx,ax #if LineSize=320 xor ch,ch ; cx = line number add cx,cx mov si,cx add si,[LineTable] mov di,[si] ; get address from table cmp di,0 ; some we can't do jz LineCopyExit #endif #if LineSize=256 mov ch,cl ; 256 byte lines... cx = cl * 256 sub ch,8 xor cl,cl mov di,cx #endif mov es,[VSSegment] ; es = VGA Screen mov si,bx ; si = bx mov cx,128 ; copy 256 bytes rep movsw LineCopyExit: pop ax,bx,cx,di,si,es ret ; ***************************************************************************** ; ; Switch to Graphics Mode ; ; ***************************************************************************** ShowGraphic: mov ah,1 ; turn off the cursor mov ch,020h int 010h mov ah,0 ; switch to 320x200 VGA mode mov al,013h int 010h call SetPalette ret ; ***************************************************************************** ; ; Switch to Text Mode ; ; ***************************************************************************** ShowText: mov ah,0 ; switch to 80x25 colour mode mov al,3 int 010h mov ah,1 ; turn cursor back on mov cx,0B0Ch int 010h ret ; ***************************************************************************** ; ; Copy Virtual Screen to Real Screen ; ; ***************************************************************************** ScreenCopy: push ax,cx,ds,es,si,di mov ax,[VSSegment] ; ds:si ^ screen line mov ds,ax mov es,0A000h #if LineSize=320 mov si,32 mov di,32 mov al,200 #else mov di,0 mov si,0 mov al,0 #endif ScrCopy2: mov cx,128 ; words to copy rep movsw add si,LineSize-256 add di,LineSize-256 dec al jnz ScrCopy2 pop di,si,es,ds,cx,ax ret ClearVS:push ax,bx,es mov es,[VSSegment] xor bx,bx xor ax,ax CVS1: mov es:[bx],ax inc bx inc bx jnz CVS1 pop es,bx,ax ret