[PATCH] sdl2: fix HighDPI display scaling

[Oliver Clarke <oliverhenryc@gmail.com>]

This makes sdl2 windows work well with dpi scaling. It fixes the issue of the display surface being stretched to fit the dpi corrected window (which created a blurry result).

Note, this does not do any scaling, it just tells the os to not scale the window. Before, when the console requested size 640x480, the logical size of the window was 640x480, and the physical size was scaled by the dpi scaling. Now, both the logical and physical size will be 640x480. This is unlike most dpi aware programs which usually do have the scaled physical size, then also make the render target that scaled size as well. This doesn't make as much sense for QEMU, since the guest is responsible for modesetting, and they should get the exact physical pixels they request (if i modeset to 3840x2160, I wouldn't want this to be scaled in any way).

Signed-off-by: Oliver Clarke <oliverhenryc@gmail.com>
---
 ui/sdl2.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ui/sdl2.c b/ui/sdl2.c
index 1c97d23a47..1910477db4 100644
--- a/ui/sdl2.c
+++ b/ui/sdl2.c
@@ -102,7 +102,7 @@ void sdl2_window_create(struct sdl2_console *scon)
         flags |= SDL_WINDOW_OPENGL;
     }
 #endif
-
+    flags |= SDL_WINDOW_ALLOW_HIGHDPI;
     scon->real_window = SDL_CreateWindow("", SDL_WINDOWPOS_UNDEFINED,
                                          SDL_WINDOWPOS_UNDEFINED,
                                          surface_width(scon->surface),
@@ -907,6 +907,7 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
     char *dir;
 
     assert(o->type == DISPLAY_TYPE_SDL);
+    SDL_SetHint(SDL_HINT_WINDOWS_DPI_AWARENESS, "permonitorv2");
 
     if (SDL_GetHintBoolean("QEMU_ENABLE_SDL_LOGGING", SDL_FALSE)) {
         SDL_LogSetAllPriority(SDL_LOG_PRIORITY_VERBOSE);
-- 
2.51.0.windows.1