Move background images into the camera

This moves background images out of the 3D viewport,
to be used only as camera reference images.

For 3D viewport references,
background images can be used, see: D2827

Some work is still needed
(background option isn't working at the moment).

release/scripts/startup/bl_ui/properties_data_camera.py

@@ -255,6 +255,107 @@ class DATA_PT_camera_dof(CameraButtonsPanel, Panel):
                 col.prop(dof_options, "blades")
 
 
+class DATA_PT_camera_background_image(CameraButtonsPanel, Panel):
+    bl_label = "Background Images"
+    bl_options = {'DEFAULT_CLOSED'}
+    COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_GAME', 'BLENDER_CLAY', 'BLENDER_EEVEE'}
+
+    def draw_header(self, context):
+        cam = context.camera
+
+        self.layout.prop(cam, "show_background_images", text="")
+
+    def draw(self, context):
+        layout = self.layout
+
+        cam = context.camera
+        use_multiview = context.scene.render.use_multiview
+
+        col = layout.column()
+        col.operator("view3d.background_image_add", text="Add Image")
+
+        for i, bg in enumerate(cam.background_images):
+            layout.active = cam.show_background_images
+            box = layout.box()
+            row = box.row(align=True)
+            row.prop(bg, "show_expanded", text="", emboss=False)
+            if bg.source == 'IMAGE' and bg.image:
+                row.prop(bg.image, "name", text="", emboss=False)
+            elif bg.source == 'MOVIE_CLIP' and bg.clip:
+                row.prop(bg.clip, "name", text="", emboss=False)
+            else:
+                row.label(text="Not Set")
+
+            if bg.show_background_image:
+                row.prop(bg, "show_background_image", text="", emboss=False, icon='RESTRICT_VIEW_OFF')
+            else:
+                row.prop(bg, "show_background_image", text="", emboss=False, icon='RESTRICT_VIEW_ON')
+
+            row.operator("view3d.background_image_remove", text="", emboss=False, icon='X').index = i
+
+            if bg.show_expanded:
+                row = box.row()
+                row.prop(bg, "source", expand=True)
+
+                has_bg = False
+                if bg.source == 'IMAGE':
+                    row = box.row()
+                    row.template_ID(bg, "image", open="image.open")
+                    if bg.image is not None:
+                        box.template_image(bg, "image", bg.image_user, compact=True)
+                        has_bg = True
+
+                        if use_multiview and bg.view_axis in {'CAMERA', 'ALL'}:
+                            box.prop(bg.image, "use_multiview")
+
+                            column = box.column()
+                            column.active = bg.image.use_multiview
+
+                            column.label(text="Views Format:")
+                            column.row().prop(bg.image, "views_format", expand=True)
+
+                            sub = column.box()
+                            sub.active = bg.image.views_format == 'STEREO_3D'
+                            sub.template_image_stereo_3d(bg.image.stereo_3d_format)
+
+                elif bg.source == 'MOVIE_CLIP':
+                    box.prop(bg, "use_camera_clip")
+
+                    column = box.column()
+                    column.active = not bg.use_camera_clip
+                    column.template_ID(bg, "clip", open="clip.open")
+
+                    if bg.clip:
+                        column.template_movieclip(bg, "clip", compact=True)
+
+                    if bg.use_camera_clip or bg.clip:
+                        has_bg = True
+
+                    column = box.column()
+                    column.active = has_bg
+                    column.prop(bg.clip_user, "proxy_render_size", text="")
+                    column.prop(bg.clip_user, "use_render_undistorted")
+
+                if has_bg:
+                    col = box.column()
+                    col.prop(bg, "alpha", slider=True)
+                    col.row().prop(bg, "draw_depth", expand=True)
+
+                    col.row().prop(bg, "frame_method", expand=True)
+
+                    box = col.box()
+                    row = box.row()
+                    row.prop(bg, "offset")
+
+                    row = box.row()
+                    row.prop(bg, "use_flip_x")
+                    row.prop(bg, "use_flip_y")
+
+                    row = box.row()
+                    row.prop(bg, "rotation")
+                    row.prop(bg, "scale")
+
+
 class DATA_PT_camera_display(CameraButtonsPanel, Panel):
     bl_label = "Display"
     COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_GAME', 'BLENDER_CLAY', 'BLENDER_EEVEE'}
@@ -344,6 +445,7 @@ classes = (
     DATA_PT_camera_stereoscopy,
     DATA_PT_camera_dof,
     DATA_PT_camera_display,
+    DATA_PT_camera_background_image,
     DATA_PT_camera_safe_areas,
     DATA_PT_custom_props_camera,
 )