[mutter] boxes: Add API to crop and scale a MetaRectangle

[Jonas Ådahl <jadahl src gnome org>]

commit d574cf59f1d5df77a9b71b9f3220beb7658b5d33
Author: Robert Mader <robert mader posteo de>
Date:   Sat Jan 5 16:39:55 2019 +0100

    boxes: Add API to crop and scale a MetaRectangle
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/323

 src/core/boxes-private.h |  6 ++++++
 src/core/boxes.c         | 16 ++++++++++++++++
 2 files changed, 22 insertions(+)
---
diff --git a/src/core/boxes-private.h b/src/core/boxes-private.h
index 5f38e6634..d80cdacd3 100644
--- a/src/core/boxes-private.h
+++ b/src/core/boxes-private.h
@@ -274,4 +274,10 @@ void meta_rectangle_transform (const MetaRectangle  *rect,
                                int                   height,
                                MetaRectangle        *dest);
 
+void meta_rectangle_crop_and_scale (const MetaRectangle *rect,
+                                    ClutterRect         *src_rect,
+                                    int                  dst_width,
+                                    int                  dst_height,
+                                    MetaRectangle       *dest);
+
 #endif /* META_BOXES_PRIVATE_H */
diff --git a/src/core/boxes.c b/src/core/boxes.c
index 7cb476d45..938ec51e9 100644
--- a/src/core/boxes.c
+++ b/src/core/boxes.c
@@ -33,6 +33,7 @@
 #include "backends/meta-monitor-transform.h"
 #include "core/boxes-private.h"
 
+#include <math.h>
 #include <X11/Xutil.h>
 
 #include "meta/util.h"
@@ -2149,3 +2150,18 @@ meta_rectangle_transform (const MetaRectangle  *rect,
       break;
     }
 }
+
+void
+meta_rectangle_crop_and_scale (const MetaRectangle *rect,
+                               ClutterRect         *src_rect,
+                               int                  dst_width,
+                               int                  dst_height,
+                               MetaRectangle       *dest)
+{
+  dest->x = floorf (rect->x * (src_rect->size.width / dst_width) +
+                    src_rect->origin.x);
+  dest->y = floorf (rect->y * (src_rect->size.height / dst_height) +
+                    src_rect->origin.y);
+  dest->width  = ceilf (rect->width * (src_rect->size.width / dst_width));
+  dest->height = ceilf (rect->height * (src_rect->size.height / dst_height));
+}