ui/console: Pass placeholder surface to displays

ui/console used to accept NULL as graphic console surface, but its
semantics was inconsistent among displays:
- cocoa and gtk-egl perform NULL dereference.
- egl-headless, spice and spice-egl do nothing.
- gtk releases underlying resources.
- sdl2-2d and sdl2-gl destroys the window.
- vnc shows a message, "Display output is not active."

Fortunately, only virtio-gpu and virtio-gpu-3d assign NULL so
we can study them to figure out the desired behavior. They assign
NULL *except* for the primary display when the device is realized,
reset, or its scanout is disabled. This effectively destroys
windows for the (uninitialized) secondary displays.

To implement the consistent behavior of display device
realization/reset, this change embeds it to the operation
switching the surface. When NULL was given as a new surface when
switching, ui/console will instead passes a placeholder down
to each display listeners.

sdl destroys the window for a secondary console if its surface is a
placeholder. The other displays simply shows the placeholder.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20210225101316.83940-2-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

6 files changed, 23 insertions, 25 deletions

diff --git a/ui/console.c b/ui/console.c
index 32823faf41..171a7bf14b 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -1675,11 +1675,26 @@ void dpy_gfx_update_full(QemuConsole *con)
 void dpy_gfx_replace_surface(QemuConsole *con,
                              DisplaySurface *surface)
 {
+    static const char placeholder_msg[] = "Display output is not active.";
     DisplayState *s = con->ds;
     DisplaySurface *old_surface = con->surface;
     DisplayChangeListener *dcl;
+    int width;
+    int height;
+
+    if (!surface) {
+        if (old_surface) {
+            width = surface_width(old_surface);
+            height = surface_height(old_surface);
+        } else {
+            width = 640;
+            height = 480;
+        }
+
+        surface = qemu_create_placeholder_surface(width, height, placeholder_msg);
+    }
 
-    assert(old_surface != surface || surface == NULL);
+    assert(old_surface != surface);
 
     con->surface = surface;
     QLIST_FOREACH(dcl, &s->listeners, next) {
diff --git a/ui/gtk.c b/ui/gtk.c
index c32ee34edc..3edaf041de 100644
--- a/ui/gtk.c
+++ b/ui/gtk.c
@@ -567,10 +567,6 @@ static void gd_switch(DisplayChangeListener *dcl,
     }
     vc->gfx.ds = surface;
 
-    if (!surface) {
-        return;
-    }
-
     if (surface->format == PIXMAN_x8r8g8b8) {
         /*
          * PIXMAN_x8r8g8b8 == CAIRO_FORMAT_RGB24
diff --git a/ui/sdl2-2d.c b/ui/sdl2-2d.c
index a2ea85127d..bfebbdeaea 100644
--- a/ui/sdl2-2d.c
+++ b/ui/sdl2-2d.c
@@ -32,14 +32,11 @@ void sdl2_2d_update(DisplayChangeListener *dcl,
                     int x, int y, int w, int h)
 {
     struct sdl2_console *scon = container_of(dcl, struct sdl2_console, dcl);
-    DisplaySurface *surf = qemu_console_surface(dcl->con);
+    DisplaySurface *surf = scon->surface;
     SDL_Rect rect;
     size_t surface_data_offset;
     assert(!scon->opengl);
 
-    if (!surf) {
-        return;
-    }
     if (!scon->texture) {
         return;
     }
@@ -75,7 +72,7 @@ void sdl2_2d_switch(DisplayChangeListener *dcl,
         scon->texture = NULL;
     }
 
-    if (!new_surface) {
+    if (is_placeholder(new_surface) && qemu_console_get_index(dcl->con)) {
         sdl2_window_destroy(scon);
         return;
     }
diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
index fd594d7461..a21d2deed9 100644
--- a/ui/sdl2-gl.c
+++ b/ui/sdl2-gl.c
@@ -86,7 +86,7 @@ void sdl2_gl_switch(DisplayChangeListener *dcl,
 
     scon->surface = new_surface;
 
-    if (!new_surface) {
+    if (is_placeholder(new_surface) && qemu_console_get_index(dcl->con)) {
         qemu_gl_fini_shader(scon->gls);
         scon->gls = NULL;
         sdl2_window_destroy(scon);
@@ -112,7 +112,7 @@ void sdl2_gl_refresh(DisplayChangeListener *dcl)
     assert(scon->opengl);
 
     graphic_hw_update(dcl->con);
-    if (scon->updates && scon->surface) {
+    if (scon->updates && scon->real_window) {
         scon->updates = 0;
         sdl2_gl_render_surface(scon);
     }
diff --git a/ui/spice-display.c b/ui/spice-display.c
index ad93b953a9..d22781a23d 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -388,7 +388,7 @@ void qemu_spice_display_switch(SimpleSpiceDisplay *ssd,
     SimpleSpiceUpdate *update;
     bool need_destroy;
 
-    if (surface && ssd->surface &&
+    if (ssd->surface &&
         surface_width(surface) == pixman_image_get_width(ssd->surface) &&
         surface_height(surface) == pixman_image_get_height(ssd->surface) &&
         surface_format(surface) == pixman_image_get_format(ssd->surface)) {
@@ -410,8 +410,8 @@ void qemu_spice_display_switch(SimpleSpiceDisplay *ssd,
 
     /* full mode switch */
     trace_qemu_spice_display_surface(ssd->qxl.id,
-                                     surface ? surface_width(surface)  : 0,
-                                     surface ? surface_height(surface) : 0,
+                                     surface_width(surface),
+                                     surface_height(surface),
                                      false);
 
     memset(&ssd->dirty, 0, sizeof(ssd->dirty));
diff --git a/ui/vnc.c b/ui/vnc.c
index 4d2151272e..310abc9378 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -790,20 +790,10 @@ static bool vnc_check_pageflip(DisplaySurface *s1,
 static void vnc_dpy_switch(DisplayChangeListener *dcl,
                            DisplaySurface *surface)
 {
-    static const char placeholder_msg[] =
-        "Display output is not active.";
-    static DisplaySurface *placeholder;
     VncDisplay *vd = container_of(dcl, VncDisplay, dcl);
     bool pageflip = vnc_check_pageflip(vd->ds, surface);
     VncState *vs;
 
-    if (surface == NULL) {
-        if (placeholder == NULL) {
-            placeholder = qemu_create_placeholder_surface(640, 480, placeholder_msg);
-        }
-        surface = placeholder;
-    }
-
     vnc_abort_display_jobs(vd);
     vd->ds = surface;