X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=3sys;a=blobdiff_plain;f=sys1%2Fkern%2Fsrc%2Fvga.c;fp=sys1%2Fkern%2Fsrc%2Fvga.c;h=ae7c04991981d0d8040d1a71e9c1145b15785739;hp=29672990a36528127b8ccdd949ee82e4e040599d;hb=a9ac2db02f009e086df85d25dc9b32452f259538;hpb=d49aa763f9b7c4ae66cf80f0cbfc3456789fc0ac

diff --git a/sys1/kern/src/vga.c b/sys1/kern/src/vga.c
index 2967299..ae7c049 100644
--- a/sys1/kern/src/vga.c
+++ b/sys1/kern/src/vga.c
@@ -28,25 +28,52 @@ void vga_setcursor(int x, int y)
 	crtc_write(CRTC_CURPOS_L, loc);
 }
 
-void vga_setstart(int start)
+void vga_scroll(int s)
 {
-	yoffs = start;
-	crtc_write(CRTC_START_H, start >> 8);
-	crtc_write(CRTC_START_L, start);
+	yoffs = s % 25;
+	s = yoffs * 80;
+	crtc_write(CRTC_START_H, s >> 8);
+	crtc_write(CRTC_START_L, s);
 }
 
 void vga_reset(void)
 {
 	vga_setcolor(VGA_WHITE, VGA_BLACK);
-	vga_setstart(0);
+	vga_scroll(0);
 	vga_setcursor(0, 0);
 	memset((void*)0xb8000, 0, 80 * 25 * 2);
 }
 
+void vga_clearline(int row)
+{
+	uint16_t *ptr;
+
+	row += yoffs;
+
+	ptr = (uint16_t*)0xb8000 + row * 80;
+	memset16(ptr, attr, 80);
+
+	if(row - 25 >= 0) {
+		/* write a copy to wrap-around future scrolling */
+		ptr -= 80 * 25;
+		memset16(ptr, attr, 80);
+	}
+}
+
 void vga_drawchar(int x, int y, int c)
 {
-	uint16_t *ptr = (uint16_t*)0xb8000 + (y + yoffs) * 80 + x;
-	*ptr = (c & 0xff) | attr;
+	uint16_t *ptr, val = (c & 0xff) | attr;
+
+	y += yoffs;
+
+	ptr = (uint16_t*)0xb8000 + y * 80 + x;
+	*ptr = val;
+
+	if(y - 25 >= 0) {
+		/* write a copy to wrap-around future scrolling */
+		ptr -= 80 * 25;
+		*ptr = val;
+	}
 }
 
 static void crtc_write(int reg, unsigned char val)