gdk: Add a request_hdr argument to begin_frame()

It's not used by anyone, it's just there.

gdk_draw_context_begin_frame_full() has been added so renderers can
make use of it.

gdk/broadway/gdkcairocontext-broadway.c

@@ -34,6 +34,7 @@ gdk_broadway_cairo_context_dispose (GObject *object)
 
 static void
 gdk_broadway_cairo_context_begin_frame (GdkDrawContext *draw_context,
+                                        gboolean        request_hdr,
                                         cairo_region_t *region)
 {
   GdkBroadwayCairoContext *self = GDK_BROADWAY_CAIRO_CONTEXT (draw_context);

gdk/broadway/gdkdrawcontext-broadway.c

@@ -34,6 +34,7 @@ gdk_broadway_draw_context_dispose (GObject *object)
 
 static void
 gdk_broadway_draw_context_begin_frame (GdkDrawContext *draw_context,
+                                       gboolean        request_hdr,
                                        cairo_region_t *region)
 {
   GdkBroadwayDrawContext *self = GDK_BROADWAY_DRAW_CONTEXT (draw_context);

gdk/gdkdrawcontext.c

@@ -307,11 +307,39 @@ void
 gdk_draw_context_begin_frame (GdkDrawContext       *context,
                               const cairo_region_t *region)
 {
-  GdkDrawContextPrivate *priv = gdk_draw_context_get_instance_private (context);
-
   g_return_if_fail (GDK_IS_DRAW_CONTEXT (context));
   g_return_if_fail (region != NULL);
 
+  gdk_draw_context_begin_frame_full (context, FALSE, region);
+}
+
+/*
+ * @request_hdr: %TRUE to request high dynamic range.
+ *
+ * If HDR is requested, GDK will see about providing a rendering target
+ * that supports high dynamic range. Typically this means a target supporting
+ * 16bit floating point pixels, but that is not guaranteed.
+ *
+ * This is only a request and if the GDK backend does not support HDR rendering
+ * or does not consider it worthwhile, it may choose to not honor the request.
+ * It may also choose to provide HDR even if it was not requested.
+ * Typically the steps undertaken by a backend are:
+ * 1. Check if HDR is supported by this drawing backend.
+ * 2. Check if the compositor supports HDR.
+ * 3. Check if the compositor prefers SDR. This is usually the case when the attached
+ *    monitors do not support HDR content or when the system is resource constrained.
+ * In either of those cases, the context will usually choose to not honor the request.
+ *
+ * The rendering code must be able to deal with HDR and SDR content, no matter if HDR
+ * was requested. The request is only a hint and GDK is free to choose.
+ */
+void
+gdk_draw_context_begin_frame_full (GdkDrawContext       *context,
+                                   gboolean              request_hdr,
+                                   const cairo_region_t *region)
+{
+  GdkDrawContextPrivate *priv = gdk_draw_context_get_instance_private (context);
+
   if (GDK_SURFACE_DESTROYED (priv->surface))
     return;
 
@@ -336,7 +364,7 @@ gdk_draw_context_begin_frame (GdkDrawContext       *context,
   priv->frame_region = cairo_region_copy (region);
   priv->surface->paint_context = g_object_ref (context);
 
-  GDK_DRAW_CONTEXT_GET_CLASS (context)->begin_frame (context, priv->frame_region);
+  GDK_DRAW_CONTEXT_GET_CLASS (context)->begin_frame (context, request_hdr, priv->frame_region);
 }
 
 #ifdef HAVE_SYSPROF

gdk/gdkdrawcontextprivate.h

@@ -41,6 +41,7 @@ struct _GdkDrawContextClass
   GObjectClass parent_class;
 
   void                  (* begin_frame)                         (GdkDrawContext         *context,
+                                                                 gboolean                request_hdr,
                                                                  cairo_region_t         *update_area);
   void                  (* end_frame)                           (GdkDrawContext         *context,
                                                                  cairo_region_t         *painted);
@@ -49,6 +50,9 @@ struct _GdkDrawContextClass
 
 void                    gdk_draw_context_surface_resized        (GdkDrawContext         *context);
 
+void                    gdk_draw_context_begin_frame_full       (GdkDrawContext         *context,
+                                                                 gboolean                request_hdr,
+                                                                 const cairo_region_t   *region);
 G_END_DECLS
 
 #endif /* __GDK__DRAW_CONTEXT_PRIVATE__ */

gdk/gdkglcontext.c

@@ -629,6 +629,7 @@ gdk_gl_context_real_make_current (GdkGLContext *context,
 
 static void
 gdk_gl_context_real_begin_frame (GdkDrawContext *draw_context,
+                                 gboolean        request_hdr,
                                  cairo_region_t *region)
 {
   GdkGLContext *context = GDK_GL_CONTEXT (draw_context);

gdk/gdkvulkancontext.c

@@ -425,6 +425,7 @@ device_supports_incremental_present (VkPhysicalDevice device)
 
 static void
 gdk_vulkan_context_begin_frame (GdkDrawContext *draw_context,
+                                gboolean        request_hdr,
                                 cairo_region_t *region)
 {
   GdkVulkanContext *context = GDK_VULKAN_CONTEXT (draw_context);

gdk/macos/gdkmacoscairocontext.c

@@ -82,6 +82,7 @@ _gdk_macos_cairo_context_cairo_create (GdkCairoContext *cairo_context)
 
 static void
 _gdk_macos_cairo_context_begin_frame (GdkDrawContext *draw_context,
+                                      gboolean        request_hdr,
                                       cairo_region_t *region)
 {
   GdkMacosCairoContext *self = (GdkMacosCairoContext *)draw_context;

gdk/macos/gdkmacosglcontext.c

@@ -291,6 +291,7 @@ opaque_region_covers_surface (GdkMacosGLContext *self)
 
 static void
 gdk_macos_gl_context_begin_frame (GdkDrawContext *context,
+                                  gboolean        request_hdr,
                                   cairo_region_t *painted)
 {
   GdkMacosGLContext *self = (GdkMacosGLContext *)context;
@@ -344,7 +345,7 @@ gdk_macos_gl_context_begin_frame (GdkDrawContext *context,
       [self->gl_context update];
     }
 
-  GDK_DRAW_CONTEXT_CLASS (gdk_macos_gl_context_parent_class)->begin_frame (context, painted);
+  GDK_DRAW_CONTEXT_CLASS (gdk_macos_gl_context_parent_class)->begin_frame (context, request_hdr, painted);
 
   if (!self->is_attached)
     {

gdk/wayland/gdkcairocontext-wayland.c

@@ -144,6 +144,7 @@ gdk_wayland_cairo_context_create_surface (GdkWaylandCairoContext *self)
 
 static void
 gdk_wayland_cairo_context_begin_frame (GdkDrawContext *draw_context,
+                                       gboolean        request_hdr,
                                        cairo_region_t *region)
 {
   GdkWaylandCairoContext *self = GDK_WAYLAND_CAIRO_CONTEXT (draw_context);

gdk/wayland/gdkglcontext-wayland.c

@@ -47,11 +47,12 @@ G_DEFINE_TYPE (GdkWaylandGLContext, gdk_wayland_gl_context, GDK_TYPE_GL_CONTEXT)
 
 static void
 gdk_wayland_gl_context_begin_frame (GdkDrawContext *draw_context,
+                                    gboolean        request_hdr,
                                     cairo_region_t *region)
 {
   gdk_wayland_surface_ensure_wl_egl_window (gdk_draw_context_get_surface (draw_context));
 
-  GDK_DRAW_CONTEXT_CLASS (gdk_wayland_gl_context_parent_class)->begin_frame (draw_context, region);
+  GDK_DRAW_CONTEXT_CLASS (gdk_wayland_gl_context_parent_class)->begin_frame (draw_context, request_hdr, region);
 
   glDrawBuffers (1, (GLenum[1]) { GL_BACK });
 }

gdk/win32/gdkcairocontext-win32.c

@@ -53,6 +53,7 @@ create_cairo_surface_for_surface (GdkSurface *surface,
 
 static void
 gdk_win32_cairo_context_begin_frame (GdkDrawContext *draw_context,
+                                     gboolean        request_hdr,
                                      cairo_region_t *region)
 {
   GdkWin32CairoContext *self = GDK_WIN32_CAIRO_CONTEXT (draw_context);

gdk/win32/gdkglcontext-win32-egl.c

@@ -471,16 +471,12 @@ gdk_win32_gl_context_egl_make_current (GdkGLContext *context,
 
 static void
 gdk_win32_gl_context_egl_begin_frame (GdkDrawContext *draw_context,
+                                      gboolean        request_hdr,
                                       cairo_region_t *update_area)
 {
-  GdkGLContext *context = GDK_GL_CONTEXT (draw_context);
-  GdkSurface *surface;
-
-  surface = gdk_gl_context_get_surface (context);
-
   gdk_win32_surface_handle_queued_move_resize (draw_context);
 
-  GDK_DRAW_CONTEXT_CLASS (gdk_win32_gl_context_egl_parent_class)->begin_frame (draw_context, update_area);
+  GDK_DRAW_CONTEXT_CLASS (gdk_win32_gl_context_egl_parent_class)->begin_frame (draw_context, request_hdr, update_area);
 }
 
 static void

gdk/win32/gdkglcontext-win32-wgl.c

@@ -118,11 +118,12 @@ gdk_win32_gl_context_wgl_end_frame (GdkDrawContext *draw_context,
 
 static void
 gdk_win32_gl_context_wgl_begin_frame (GdkDrawContext *draw_context,
+                                      gboolean        request_hdr,
                                       cairo_region_t *update_area)
 {
   gdk_win32_surface_handle_queued_move_resize (draw_context);
 
-  GDK_DRAW_CONTEXT_CLASS (gdk_win32_gl_context_wgl_parent_class)->begin_frame (draw_context, update_area);
+  GDK_DRAW_CONTEXT_CLASS (gdk_win32_gl_context_wgl_parent_class)->begin_frame (draw_context, request_hdr, update_area);
 }
 
 static int

gdk/win32/gdkvulkancontext-win32.c

@@ -68,11 +68,12 @@ gdk_win32_vulkan_context_create_surface (GdkVulkanContext *context,
 
 static void
 gdk_win32_vulkan_context_begin_frame (GdkDrawContext *draw_context,
+                                      gboolean        request_hdr,
                                       cairo_region_t *update_area)
 {
   gdk_win32_surface_handle_queued_move_resize (draw_context);
 
-  GDK_DRAW_CONTEXT_CLASS (gdk_win32_vulkan_context_parent_class)->begin_frame (draw_context, update_area);
+  GDK_DRAW_CONTEXT_CLASS (gdk_win32_vulkan_context_parent_class)->begin_frame (draw_context, request_hdr, update_area);
 }
 
 static void

gdk/x11/gdkcairocontext-x11.c

@@ -55,6 +55,7 @@ create_cairo_surface_for_surface (GdkSurface *surface)
 
 static void
 gdk_x11_cairo_context_begin_frame (GdkDrawContext *draw_context,
+                                   gboolean        request_hdr,
                                    cairo_region_t *region)
 {
   GdkX11CairoContext *self = GDK_X11_CAIRO_CONTEXT (draw_context);

gdk/x11/gdkglcontext-egl.c

@@ -61,9 +61,10 @@ gdk_x11_display_get_egl_display (GdkDisplay *display)
 
 static void
 gdk_x11_gl_context_egl_begin_frame (GdkDrawContext *draw_context,
+                                    gboolean        request_hdr,
                                     cairo_region_t *region)
 {
-  GDK_DRAW_CONTEXT_CLASS (gdk_x11_gl_context_egl_parent_class)->begin_frame (draw_context, region);
+  GDK_DRAW_CONTEXT_CLASS (gdk_x11_gl_context_egl_parent_class)->begin_frame (draw_context, request_hdr, region);
 
   glDrawBuffers (1, (GLenum[1]) { GL_BACK });
 }