ui/gtk: Add scale option

Allow user to set a preferred scale (defaulting to 1) of the virtual
display. Along with zoom-to-fix=false, this would be helpful for users
running QEMU on hi-dpi host desktop to achieve pixel to pixel display --
e.g., if the scale factor of a user's host desktop is set to 200%, then
they can set a 0.5 scale for the virtual display to avoid magnification
that might cause blurriness.

Signed-off-by: Weifeng Liu <weifeng.liu.z@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20250601045245.36778-3-weifeng.liu.z@gmail.com>

1 files changed, 29 insertions, 17 deletions

diff --git a/ui/gtk.c b/ui/gtk.c
index 9104509ee1..e91d093a49 100644
--- a/ui/gtk.c
+++ b/ui/gtk.c
@@ -67,6 +67,7 @@
 #define VC_TERM_X_MIN     80
 #define VC_TERM_Y_MIN     25
 #define VC_SCALE_MIN    0.25
+#define VC_SCALE_MAX       4
 #define VC_SCALE_STEP   0.25
 
 #ifdef GDK_WINDOWING_X11
@@ -272,15 +273,11 @@ static void gd_update_geometry_hints(VirtualConsole *vc)
         if (!vc->gfx.ds) {
             return;
         }
-        if (s->free_scale) {
-            geo.min_width  = surface_width(vc->gfx.ds) * VC_SCALE_MIN;
-            geo.min_height = surface_height(vc->gfx.ds) * VC_SCALE_MIN;
-            mask |= GDK_HINT_MIN_SIZE;
-        } else {
-            geo.min_width  = surface_width(vc->gfx.ds) * vc->gfx.scale_x;
-            geo.min_height = surface_height(vc->gfx.ds) * vc->gfx.scale_y;
-            mask |= GDK_HINT_MIN_SIZE;
-        }
+        double scale_x = s->free_scale ? VC_SCALE_MIN : vc->gfx.scale_x;
+        double scale_y = s->free_scale ? VC_SCALE_MIN : vc->gfx.scale_y;
+        geo.min_width  = surface_width(vc->gfx.ds) * scale_x;
+        geo.min_height = surface_height(vc->gfx.ds) * scale_y;
+        mask |= GDK_HINT_MIN_SIZE;
         geo_widget = vc->gfx.drawing_area;
         gtk_widget_set_size_request(geo_widget, geo.min_width, geo.min_height);
 
@@ -1579,8 +1576,8 @@ static void gd_menu_full_screen(GtkMenuItem *item, void *opaque)
         }
         s->full_screen = FALSE;
         if (vc->type == GD_VC_GFX) {
-            vc->gfx.scale_x = 1.0;
-            vc->gfx.scale_y = 1.0;
+            vc->gfx.scale_x = vc->gfx.preferred_scale;
+            vc->gfx.scale_y = vc->gfx.preferred_scale;
             gd_update_windowsize(vc);
         }
     }
@@ -1636,8 +1633,8 @@ static void gd_menu_zoom_fixed(GtkMenuItem *item, void *opaque)
     GtkDisplayState *s = opaque;
     VirtualConsole *vc = gd_vc_find_current(s);
 
-    vc->gfx.scale_x = 1.0;
-    vc->gfx.scale_y = 1.0;
+    vc->gfx.scale_x = vc->gfx.preferred_scale;
+    vc->gfx.scale_y = vc->gfx.preferred_scale;
 
     gd_update_windowsize(vc);
 }
@@ -1651,8 +1648,8 @@ static void gd_menu_zoom_fit(GtkMenuItem *item, void *opaque)
         s->free_scale = TRUE;
     } else {
         s->free_scale = FALSE;
-        vc->gfx.scale_x = 1.0;
-        vc->gfx.scale_y = 1.0;
+        vc->gfx.scale_x = vc->gfx.preferred_scale;
+        vc->gfx.scale_y = vc->gfx.preferred_scale;
     }
 
     gd_update_windowsize(vc);
@@ -2243,6 +2240,11 @@ static void gl_area_realize(GtkGLArea *area, VirtualConsole *vc)
 }
 #endif
 
+static bool gd_scale_valid(double scale)
+{
+    return scale >= VC_SCALE_MIN && scale <= VC_SCALE_MAX;
+}
+
 static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
                               QemuConsole *con, int idx,
                               GSList *group, GtkWidget *view_menu)
@@ -2252,8 +2254,18 @@ static GSList *gd_vc_gfx_init(GtkDisplayState *s, VirtualConsole *vc,
 
     vc->label = qemu_console_get_label(con);
     vc->s = s;
-    vc->gfx.scale_x = 1.0;
-    vc->gfx.scale_y = 1.0;
+    vc->gfx.preferred_scale = 1.0;
+    if (s->opts->u.gtk.has_scale) {
+        if (gd_scale_valid(s->opts->u.gtk.scale)) {
+            vc->gfx.preferred_scale = s->opts->u.gtk.scale;
+        } else {
+            error_report("Invalid scale value %lf given, being ignored",
+                         s->opts->u.gtk.scale);
+            s->opts->u.gtk.has_scale = false;
+        }
+    }
+    vc->gfx.scale_x = vc->gfx.preferred_scale;
+    vc->gfx.scale_y = vc->gfx.preferred_scale;
 
 #if defined(CONFIG_OPENGL)
     if (display_opengl) {