sm501: Implement negated destination raster operation mode

Add support for the negated destination operation mode. This is used e.g.
by AmigaOS for the INVERSEVID drawing mode. With this change, the cursor
in the shell and non-immediate window adjustment are working now.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/display/sm501.c

@@ -705,6 +705,8 @@ static void sm501_2d_operation(SM501State *s)
     uint32_t color = s->twoD_foreground;
     int format_flags = (s->twoD_stretch >> 20) & 0x3;
     int addressing = (s->twoD_stretch >> 16) & 0xF;
+    int rop_mode = (s->twoD_control >> 15) & 0x1; /* 1 for rop2, else rop3 */
+    int rop = s->twoD_control & 0xFF;
 
     /* get frame buffer info */
     uint8_t *src = s->local_mem + (s->twoD_source_base & 0x03FFFFFF);
@@ -729,6 +731,8 @@ static void sm501_2d_operation(SM501State *s)
         int y, x, index_d, index_s;                                           \
         for (y = 0; y < operation_height; y++) {                              \
             for (x = 0; x < operation_width; x++) {                           \
+                _pixel_type val;                                              \
+                                                                              \
                 if (rtl) {                                                    \
                     index_s = ((src_y - y) * src_width + src_x - x) * _bpp;   \
                     index_d = ((dst_y - y) * dst_width + dst_x - x) * _bpp;   \
@@ -736,7 +740,13 @@ static void sm501_2d_operation(SM501State *s)
                     index_s = ((src_y + y) * src_width + src_x + x) * _bpp;   \
                     index_d = ((dst_y + y) * dst_width + dst_x + x) * _bpp;   \
                 }                                                             \
-                *(_pixel_type *)&dst[index_d] = *(_pixel_type *)&src[index_s];\
+                if (rop_mode == 1 && rop == 5) {                              \
+                    /* Invert dest */                                         \
+                    val = ~*(_pixel_type *)&dst[index_d];                     \
+                } else {                                                      \
+                    val = *(_pixel_type *)&src[index_s];                      \
+                }                                                             \
+                *(_pixel_type *)&dst[index_d] = val;                          \
             }                                                                 \
         }                                                                     \
     }