graphics: trivial optimization of old-style graphic modesyslinux-3.83-pre4

Trivially optimize the old-style graphics by using another level of
temporary buffering in bitplane format, thereby enabling the use of
rep movsd to write the contents to the screen.  This can speed things
up substantially in virtualization environments.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 47 insertions, 24 deletions

diff --git a/core/graphics.inc b/core/graphics.inc
index 3ba51465..884776ea 100644
--- a/core/graphics.inc
+++ b/core/graphics.inc
@@ -75,22 +75,26 @@ vgadisplayfile:
 		mov di,VGARowBuffer
 		; Pre-clear the row buffer
 		push di
+		push di
 		mov cx,640/4
 		xor eax,eax
 		rep stosd
 		pop di
-		push di
 		mov cx,[GraphXSize]
 		call rledecode			; Decode one row
 		pop si
+		mov di,VGAPlaneBuffer
+		push di
+		mov bp,640
+		call packedpixel2vga
+		pop si
 		push es
 		mov di,0A000h			; VGA segment
 		mov es,di
 		mov di,[VGAPos]
-		mov bp,640
-		call packedpixel2vga
-		add word [VGAPos],80
+		call outputvga
 		pop es
+		add word [VGAPos],640/8
 		pop cx
 		loop .drawpixelrow
 
@@ -160,39 +164,57 @@ rledecode:
 ;
 ; DS:SI -> packed pixel string
 ; BP    -> pixel count (multiple of 8)
-; ES:DI -> output
+; DS:DI -> output (four planes)
 ;
 packedpixel2vga:
-		mov dx,3C4h	; VGA Sequencer Register select port
-		mov al,2	; Sequencer mask
-		out dx,al	; Select the sequencer mask
-		inc dx		; VGA Sequencer Register data port
-		mov al,1
-		mov bl,al
+		xor cx,cx
 .planeloop:
-		pusha
-		out dx,al
+		inc cx
+		push si
+		push bp
 .loop1:
-		mov cx,8
+		mov bx,8
 .loop2:
-		xchg cx,bx
 		lodsb
 		shr al,cl
-		rcl ch,1	; VGA is bigendian.  Sigh.
-		xchg cx,bx
-		loop .loop2
-		mov al,bh
-		stosb
+		rcl dl,1		; VGA is bigendian.  Sigh.
+		dec bx
+		jnz .loop2
+		mov [di],dl
+		inc di
 		sub bp,byte 8
 		ja .loop1
-		popa
-		inc bl
-		shl al,1
-		cmp bl,4
+		pop bp
+		pop si
+		cmp cl,3
 		jbe .planeloop
 		ret
 
 ;
+; outputvga:
+;	Output four subsequent lines of VGA data
+;
+; DS:SI	-> four planes @ 640/8=80 bytes
+; ES:DI	-> pointer into VGA memory
+;
+outputvga:
+		mov dx,3C4h	; VGA Sequencer Register select port
+		mov al,2	; Sequencer mask
+		out dx,al	; Select the sequencer mask
+		inc dx		; VGA Sequencer Register data port
+		dec ax		; AL <- 1
+.loop1:
+		out dx,al	; Select the bit plane to write
+		push di
+		mov cx,640/8
+		rep movsb
+		pop di
+		add ax,ax
+		cmp al,8
+		jbe .loop1
+		ret
+
+;
 ; vgasetmode:
 ;	Enable VGA graphics, if possible; return ZF=1 on success
 ;	DS must be set to the base segment; ES is set to DS.
@@ -328,3 +350,4 @@ VGAFileMBuf	resb FILENAME_MAX	; Mangled VGA image name
 
 		alignb 4
 VGARowBuffer	resb 640+80		; Decompression buffer
+VGAPlaneBuffer	resb (640/8)*4		; Plane buffers