sdl: add support for high resolution window icon

Modern desktop environments can render icons at very large sizes,
especially with high DPI screens. Providing a 32x32 pixel bitmap is
nowhere near sufficient anymore.

When displayed in GNOME shell the QEMU icon looks awful, having been
scaled up to at least x4 its base size. This is compounded by the fact
that the BMP file doesn't do transparency, so while we've removed white
pixels, we still have anti-aliased nearly-white pixels which make the
logo look appalling on black backgrounds.

Loading a high resolution PNG icon addresses both problems, but requires
use of the extra SDL2_image library.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20190110120047.25369-4-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

configure

@@ -346,6 +346,7 @@ fdt=""
 netmap="no"
 sdl=""
 sdlabi=""
+sdl_image=""
 virtfs=""
 mpath=""
 vnc="yes"
@@ -1042,6 +1043,10 @@ for opt do
   ;;
   --with-sdlabi=*) sdlabi="$optarg"
   ;;
+  --disable-sdl-image) sdl_image="no"
+  ;;
+  --enable-sdl-image) sdl_image="yes"
+  ;;
   --disable-qom-cast-debug) qom_cast_debug="no"
   ;;
   --enable-qom-cast-debug) qom_cast_debug="yes"
@@ -1704,6 +1709,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   gcrypt          libgcrypt cryptography support
   sdl             SDL UI
   --with-sdlabi     select preferred SDL ABI 1.2 or 2.0
+  sdl_image       SDL Image support for icons
   gtk             gtk UI
   vte             vte support for the gtk UI
   curses          curses UI
@@ -3002,10 +3008,43 @@ EOF
   fi # sdl compile test
 }
 
+sdl_image_probe ()
+{
+    if test "$sdl_image" != "no" ; then
+        if $pkg_config SDL2_image --exists; then
+            if test "$static" = "yes"; then
+                sdl_image_libs=$($pkg_config SDL2_image --libs --static 2>/dev/null)
+            else
+                sdl_image_libs=$($pkg_config SDL2_image --libs 2>/dev/null)
+            fi
+            sdl_image_cflags=$($pkg_config SDL2_image --cflags 2>/dev/null)
+            sdl_image=yes
+
+            sdl_cflags="$sdl_cflags $sdl_image_cflags"
+            sdl_libs="$sdl_libs $sdl_image_libs"
+        else
+            if test "$sdl_image" = "yes" ; then
+                feature_not_found "sdl_image" "Install SDL Image devel"
+            else
+                sdl_image=no
+            fi
+        fi
+    fi
+}
+
 if test "$sdl" != "no" ; then
   sdl_probe
 fi
 
+if test "$sdl" = "yes" ; then
+  sdl_image_probe
+else
+  if test "$sdl_image" = "yes"; then
+    echo "warning: SDL Image requested, but SDL is not available, disabling"
+  fi
+  sdl_image=no
+fi
+
 if test "$sdl" = "yes" ; then
   cat > $TMPC <<EOF
 #include <SDL.h>
@@ -6029,6 +6068,7 @@ if test "$darwin" = "yes" ; then
     echo "Cocoa support     $cocoa"
 fi
 echo "SDL support       $sdl $(echo_version $sdl $sdlversion)"
+echo "SDL image support $sdl_image"
 echo "GTK support       $gtk $(echo_version $gtk $gtk_version)"
 echo "GTK GL support    $gtk_gl"
 echo "VTE support       $vte $(echo_version $vte $vteversion)"
@@ -6368,6 +6408,9 @@ if test "$sdl" = "yes" ; then
   echo "CONFIG_SDLABI=$sdlabi" >> $config_host_mak
   echo "SDL_CFLAGS=$sdl_cflags" >> $config_host_mak
   echo "SDL_LIBS=$sdl_libs" >> $config_host_mak
+  if test "$sdl_image" = "yes" ; then
+      echo "CONFIG_SDL_IMAGE=y" >> $config_host_mak
+  fi
 fi
 if test "$cocoa" = "yes" ; then
   echo "CONFIG_COCOA=y" >> $config_host_mak

include/ui/sdl2.h

@@ -6,6 +6,9 @@
 
 #include <SDL.h>
 #include <SDL_syswm.h>
+#ifdef CONFIG_SDL_IMAGE
+# include <SDL_image.h>
+#endif
 
 #ifdef CONFIG_OPENGL
 # include "ui/egl-helpers.h"

ui/sdl2.c

@@ -764,6 +764,7 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
     uint8_t data = 0;
     int i;
     SDL_SysWMinfo info;
+    SDL_Surface *icon = NULL;
 
     assert(o->type == DISPLAY_TYPE_SDL);
 
@@ -835,13 +836,18 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
 #endif
     }
 
+#ifdef CONFIG_SDL_IMAGE
+    icon = IMG_Load(CONFIG_QEMU_ICONDIR "/hicolor/128x128/apps/qemu.png");
+#else
     /* Load a 32x32x4 image. White pixels are transparent. */
-    SDL_Surface *image = SDL_LoadBMP(CONFIG_QEMU_ICONDIR
+    icon = SDL_LoadBMP(CONFIG_QEMU_ICONDIR "/hicolor/32x32/apps/qemu.bmp");
-                                     "/hicolor/32x32/apps/qemu.bmp");
+    if (icon) {
-    if (image) {
+        uint32_t colorkey = SDL_MapRGB(icon->format, 255, 255, 255);
-        uint32_t colorkey = SDL_MapRGB(image->format, 255, 255, 255);
+        SDL_SetColorKey(icon, SDL_TRUE, colorkey);
-        SDL_SetColorKey(image, SDL_TRUE, colorkey);
+    }
-        SDL_SetWindowIcon(sdl2_console[0].real_window, image);
+#endif
+    if (icon) {
+        SDL_SetWindowIcon(sdl2_console[0].real_window, icon);
     }
 
     gui_grab = 0;