[RFC PATCH 4/5] hw/display/artist: Avoid drawing line when nothing to display

[Philippe Mathieu-Daudé]

Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
---
RFC because untested =)
---
 hw/display/artist.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/display/artist.c b/hw/display/artist.c
index 97c811b35e..5492079116 100644
--- a/hw/display/artist.c
+++ b/hw/display/artist.c
@@ -557,90 +557,93 @@ static void fill_window(ARTISTState *s, int startx, int 
starty,
 static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
                       bool update_start, int skip_pix, int max_pix)
 {
     struct vram_buffer *buf;
     uint8_t color;
     int dx, dy, t, e, x, y, incy, diago, horiz;
     bool c1;
     uint8_t *p;
 
     trace_artist_draw_line(x1, y1, x2, y2);
 
     if (update_start) {
         s->vram_start = (x2 << 16) | y2;
     }
 
     if (x2 > x1) {
         dx = x2 - x1;
     } else {
         dx = x1 - x2;
     }
     if (y2 > y1) {
         dy = y2 - y1;
     } else {
         dy = y1 - y2;
     }
+    if (!dx || !dy) {
+        return;
+    }
 
     c1 = false;
     if (dy > dx) {
         t = y2;
         y2 = x2;
         x2 = t;
 
         t = y1;
         y1 = x1;
         x1 = t;
 
         t = dx;
         dx = dy;
         dy = t;
 
         c1 = true;
     }
 
     if (x1 > x2) {
         t = y2;
         y2 = y1;
         y1 = t;
 
         t = x1;
         x1 = x2;
         x2 = t;
     }
 
     horiz = dy << 1;
     diago = (dy - dx) << 1;
     e = (dy << 1) - dx;
 
     if (y1 <= y2) {
         incy = 1;
     } else {
         incy = -1;
     }
     x = x1;
     y = y1;
     color = artist_get_color(s);
     buf = &s->vram_buffer[ARTIST_BUFFER_AP];
 
     do {
         if (c1) {
             p = buf->data + x * s->width + y;
         } else {
             p = buf->data + y * s->width + x;
         }
 
         if (skip_pix > 0) {
             skip_pix--;
         } else {
             artist_rop8(s, p, color);
         }
 
         if (e > 0) {
             artist_invalidate_lines(buf, y, 1);
             y  += incy;
             e  += diago;
         } else {
             e += horiz;
         }
         x++;
     } while (x <= x2 && (max_pix == -1 || --max_pix > 0));
 }
-- 
2.21.1