1 files changed, 76 insertions, 4 deletions

diff --git a/source/zx81.c b/source/zx81.c
index 7964ed1..81cfd55 100644
--- a/source/zx81.c
+++ b/source/zx81.c
@@ -19,7 +19,7 @@
 
     -------------------------------------------------------------------------
 
-    Provides the emulation for the zX81
+    Provides the emulation for the ZX81
 
 */
 #include <stdlib.h>
@@ -82,6 +82,8 @@ static int		last_I;
 
 static Z80Byte		mem[0x10000];
 
+static Z80Byte		scr_mirror[7000];
+
 static Z80Word		RAMBOT=0;
 static Z80Word		RAMTOP=0;
 static Z80Word		RAMLEN=0;
@@ -366,14 +368,80 @@ static void ClearText(void)
 }
 
 
-static void DrawScreen_HIRES(Z80 *z80)
+static void DrawScreen_HIRES_Dirty(Z80 *z80)
+{
+    uint16 *bmp;
+    Z80Byte *scr;
+    Z80Byte *mirror;
+    int x,y;
+    int table;
+    int c;
+    int v;
+    int b;
+
+    scr = mem + hires_dfile;
+    mirror = scr_mirror;
+    bmp = bmp_screen;
+    table = z80->I << 8;
+
+    /* scr is increment in both loops so that it can skip the end-of-line
+       character
+    */
+    for(y=0; y<192; y++)
+    {
+    	for(x=0; x<32; x++)
+	{
+	    c = *scr;
+
+	    if (c != *mirror)
+	    {
+	    	*mirror++ = c;
+
+		v = mem[table + (c&0x3f)*8];
+
+		if (c & 0x80)
+		{
+		    v ^= 0xff;
+		}
+
+		for(b=0;b<8;b++)
+		{
+		    if (v & 0x80)
+		    {
+			*bmp++ = 0x8000;
+		    }
+		    else
+		    {
+			*bmp++ = 0xffff;
+		    }
+
+		    v=v<<1;
+		}
+	    }
+	    else
+	    {
+	    	mirror++;
+		bmp+=8;
+	    }
+
+	    scr++;
+	}
+
+	scr++;
+    }
+}
+
+
+static void DrawScreen_HIRES_Full(Z80 *z80)
 {
     uint16 *bmp;
     Z80Byte *scr;
+    Z80Byte *mirror;
     int x,y;
     int table;
 
     scr = mem + hires_dfile;
+    mirror = scr_mirror;
     bmp = bmp_screen;
     table = z80->I << 8;
 
@@ -388,7 +456,7 @@ static void DrawScreen_HIRES(Z80 *z80)
 	    int v;
 	    int b;
 
-	    c = *scr;
+	    c = *mirror++ = *scr;
 
 	    v = mem[table + (c&0x3f)*8];
 
@@ -416,8 +484,11 @@ static void DrawScreen_HIRES(Z80 *z80)
 
 	scr++;
     }
+
+    DrawScreen = DrawScreen_HIRES_Dirty;
 }
 
+
 static void DrawScreen_TEXT(Z80 *z80)
 {
     Z80Byte *scr=mem+WORD(DFILE);
@@ -617,7 +688,8 @@ static int CheckTimers(Z80 *z80, Z80Val val)
 	    else
 	    {
 	    	hires = TRUE;
-		DrawScreen = DrawScreen_HIRES;
+		DrawScreen = DrawScreen_HIRES_Full;
+		ClearBitmap();
 		ClearText();
 		FindHiresDFILE();
 	    }