[gimp] app: in GimpCanvasBufferPreview, add support for offset buffers

[Ell <ell src gnome org>]

commit 43f8a5199fa97d68c0733ef6f63da6b2c380a252
Author: Ell <ell_se yahoo com>
Date:   Mon Feb 3 20:03:57 2020 +0200

    app: in GimpCanvasBufferPreview, add support for offset buffers
    
    Ditto.

 app/display/gimpcanvasbufferpreview.c | 74 +++++++++++++++++------------------
 1 file changed, 35 insertions(+), 39 deletions(-)
---
diff --git a/app/display/gimpcanvasbufferpreview.c b/app/display/gimpcanvasbufferpreview.c
index 6aad7f2ed1..26b1171787 100644
--- a/app/display/gimpcanvasbufferpreview.c
+++ b/app/display/gimpcanvasbufferpreview.c
@@ -25,9 +25,12 @@
 #include <cairo/cairo.h>
 
 #include "libgimpbase/gimpbase.h"
+#include "libgimpmath/gimpmath.h"
 
 #include "display/display-types.h"
 
+#include "core/gimpimage.h"
+
 #include "gimpcanvas.h"
 #include "gimpcanvasbufferpreview.h"
 #include "gimpdisplayshell.h"
@@ -150,17 +153,9 @@ gimp_canvas_buffer_preview_draw (GimpCanvasItem *item,
   cairo_surface_t       *area;
   guchar                *data;
   cairo_rectangle_int_t  rectangle;
-  gint                   viewport_offset_x, viewport_offset_y;
-  gint                   viewport_width,    viewport_height;
 
   g_return_if_fail (GEGL_IS_BUFFER (buffer));
 
-  gimp_display_shell_scroll_get_scaled_viewport (shell,
-                                                 &viewport_offset_x,
-                                                 &viewport_offset_y,
-                                                 &viewport_width,
-                                                 &viewport_height);
-
   gimp_canvas_buffer_preview_compute_bounds (item, &rectangle);
 
   area = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
@@ -169,8 +164,8 @@ gimp_canvas_buffer_preview_draw (GimpCanvasItem *item,
 
   data = cairo_image_surface_get_data (area);
   gegl_buffer_get (buffer,
-                   GEGL_RECTANGLE ((viewport_offset_x < 0 ? 0 : viewport_offset_x),
-                                   (viewport_offset_y < 0 ? 0 : viewport_offset_y),
+                   GEGL_RECTANGLE (rectangle.x + shell->offset_x,
+                                   rectangle.y + shell->offset_y,
                                    rectangle.width,
                                    rectangle.height),
                    shell->scale_x,
@@ -197,38 +192,39 @@ gimp_canvas_buffer_preview_compute_bounds (GimpCanvasItem        *item,
 {
   GimpDisplayShell *shell  = gimp_canvas_item_get_shell (item);
   GeglBuffer       *buffer = GET_PRIVATE (item)->buffer;
-  gint              x_from, x_to;
-  gint              y_from, y_to;
-  gint              viewport_offset_x, viewport_offset_y;
-  gint              viewport_width,    viewport_height;
-  gint              width, height;
+  GeglRectangle     extent;
+  gdouble           x1, y1;
+  gdouble           x2, y2;
 
   g_return_if_fail (GEGL_IS_BUFFER (buffer));
 
-  width  = gegl_buffer_get_width  (buffer);
-  height = gegl_buffer_get_height (buffer);
-
-  gimp_display_shell_scroll_get_scaled_viewport (shell,
-                                                 &viewport_offset_x,
-                                                 &viewport_offset_y,
-                                                 &viewport_width,
-                                                 &viewport_height);
-
-  x_from = (viewport_offset_x < 0 ? -viewport_offset_x : 0);
-  y_from = (viewport_offset_y < 0 ? -viewport_offset_y : 0);
-
-  x_to = width * shell->scale_x - viewport_offset_x;
-  if (x_to > viewport_width)
-    x_to = viewport_width;
-
-  y_to = height * shell->scale_y - viewport_offset_y;
-  if (y_to > viewport_height)
-    y_to = viewport_height;
-
-  bounds->x      = x_from;
-  bounds->y      = y_from;
-  bounds->width  = x_to - x_from;
-  bounds->height = y_to - y_from;
+  extent = *gegl_buffer_get_extent (buffer);
+
+  gimp_canvas_item_transform_xy_f (item,
+                                   extent.x,
+                                   extent.y,
+                                   &x1, &y1);
+  gimp_canvas_item_transform_xy_f (item,
+                                   extent.x + extent.width,
+                                   extent.y + extent.height,
+                                   &x2, &y2);
+
+  extent.x      = floor (x1);
+  extent.y      = floor (y1);
+  extent.width  = ceil  (x2) - extent.x;
+  extent.height = ceil  (y2) - extent.y;
+
+  gegl_rectangle_intersect (&extent,
+                            &extent,
+                            GEGL_RECTANGLE (0,
+                                            0,
+                                            shell->disp_width,
+                                            shell->disp_height));
+
+  bounds->x      = extent.x;
+  bounds->y      = extent.y;
+  bounds->width  = extent.width;
+  bounds->height = extent.height;
 }
 
 static cairo_region_t *