[evince] libview: Fix support for HiDPI in link preview

[Germán Poo-Caamaño <gpoo src gnome org>]

commit caad329a6fb19ddcf1d61de2b3debdd0228faa37
Author: Mads Chr. Olesen <mads mchro dk>
Date:   Wed Jan 27 20:53:29 2021 +0100

    libview: Fix support for HiDPI in link preview
    
    When showing link preview popover we should take device_scale
    into consideration.
    
    Two cases must be handled:
    1. If we get the page_surface from the ev_pixbuf_cache
       (this typically happens if link is to same page or within +/- 10
    pages)
    2. If we render the page_surface by our own job
       (this typically happins if link is more than 10 pages away)
    
    Fixes #1543

 libview/ev-view.c | 74 +++++++++++++++++++++++++++++++------------------------
 1 file changed, 42 insertions(+), 32 deletions(-)
---
diff --git a/libview/ev-view.c b/libview/ev-view.c
index e2ca6b5a..5301d65f 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -158,7 +158,7 @@ static void       get_link_area                              (EvView
                                                              gint                y,
                                                              EvLink             *link,
                                                              GdkRectangle       *area);
-static void       link_preview_show_thumbnail                (GdkPixbuf          *pixbuf,
+static void       link_preview_show_thumbnail                (cairo_surface_t    *page_surface,
                                                              EvView             *view);
 static void       link_preview_job_finished_cb               (EvJobThumbnail     *job,
                                                              EvView             *view);
@@ -2223,6 +2223,7 @@ ev_view_handle_cursor_over_xy (EvView *view, gint x, gint y)
                guint            link_dest_page;
                EvPoint          link_dest_doc;
                GdkPoint         link_dest_view;
+               gint             device_scale = 1;
 
                ev_view_set_cursor (view, EV_VIEW_CURSOR_LINK);
 
@@ -2262,10 +2263,13 @@ ev_view_handle_cursor_over_xy (EvView *view, gint x, gint y)
 
                /* Start thumbnailing job async */
                link_dest_page = ev_link_dest_get_page (dest);
+#ifdef HAVE_HIDPI_SUPPORT
+               device_scale = gtk_widget_get_scale_factor (GTK_WIDGET (view));
+#endif
                view->link_preview.job = ev_job_thumbnail_new (view->document,
                                                               link_dest_page,
                                                               view->rotation,
-                                                              view->scale);
+                                                              view->scale * device_scale);
                ev_job_thumbnail_set_output_format (EV_JOB_THUMBNAIL (view->link_preview.job),
                                                    EV_JOB_THUMBNAIL_SURFACE);
 
@@ -2279,15 +2283,9 @@ ev_view_handle_cursor_over_xy (EvView *view, gint x, gint y)
 
                page_surface = ev_pixbuf_cache_get_surface (view->pixbuf_cache, link_dest_page);
 
-               if (page_surface) {
-                       GdkPixbuf *slice;
-
-                       slice = gdk_pixbuf_get_from_surface (page_surface, 0, 0,
-                                                            cairo_image_surface_get_width(page_surface),
-                                                            cairo_image_surface_get_height(page_surface));
-                       link_preview_show_thumbnail (slice, view);
-                       g_object_unref(slice);
-               } else {
+               if (page_surface)
+                       link_preview_show_thumbnail (page_surface, view);
+               else {
                        g_signal_connect (view->link_preview.job, "finished",
                                          G_CALLBACK (link_preview_job_finished_cb),
                                          view);
@@ -5169,23 +5167,28 @@ get_field_area (EvView       *view,
 }
 
 static void
-link_preview_show_thumbnail (GdkPixbuf *pixbuf,
+link_preview_show_thumbnail (cairo_surface_t *page_surface,
                             EvView *view)
 {
-       GtkWidget *popover = view->link_preview.popover;
-       GdkPixbuf *thumbnail_slice;
-       GtkWidget *image_view;
-       gdouble    x, y;   /* position of the link on destination page */
-       gint       pwidth, pheight;  /* dimensions of destination page */
-       gint       vwidth, vheight;  /* dimensions of main view */
-       gint       width, height;    /* dimensions of popup */
-       gint       left, top;
+       GtkWidget       *popover = view->link_preview.popover;
+       GtkWidget       *image_view;
+       gdouble          x, y;   /* position of the link on destination page */
+       gint             pwidth, pheight;  /* dimensions of destination page */
+       gint             vwidth, vheight;  /* dimensions of main view */
+       gint             width, height;    /* dimensions of popup */
+       gint             left, top;
+       gdouble          device_scale_x = 1, device_scale_y = 1;
+       cairo_surface_t *thumbnail_slice;
+       cairo_t         *cr;
 
        x = view->link_preview.left;
        y = view->link_preview.top;
 
-       pwidth = gdk_pixbuf_get_width (pixbuf);
-       pheight = gdk_pixbuf_get_height (pixbuf);
+#ifdef HAVE_HIDPI_SUPPORT
+       cairo_surface_get_device_scale (page_surface, &device_scale_x, &device_scale_y);
+#endif
+       pwidth = cairo_image_surface_get_width (page_surface) / device_scale_x;
+       pheight = cairo_image_surface_get_height (page_surface) / device_scale_y;
 
        vwidth = gtk_widget_get_allocated_width (GTK_WIDGET (view));
        vheight = gtk_widget_get_allocated_height (GTK_WIDGET (view));
@@ -5218,16 +5221,21 @@ link_preview_show_thumbnail (GdkPixbuf *pixbuf,
        left = MIN (MAX (0, left), pwidth - width);
        top = MIN (MAX (0, top), pheight - height);
 
-       thumbnail_slice = gdk_pixbuf_new_subpixbuf (pixbuf,
-                                                   left, top,
-                                                   width, height);
-       image_view = gtk_image_new_from_pixbuf (thumbnail_slice);
+       /* paint out the part of the page we want to a separate cairo_surface_t */
+       thumbnail_slice = cairo_surface_create_similar (page_surface, CAIRO_CONTENT_COLOR, width, height);
+       cr = cairo_create (thumbnail_slice);
+       cairo_set_source_surface (cr, page_surface, -left, -top);
+       cairo_rectangle (cr, 0, 0, width, height);
+       cairo_fill (cr);
+
+       image_view = gtk_image_new_from_surface (thumbnail_slice);
 
        gtk_widget_destroy (gtk_bin_get_child (GTK_BIN (popover)));
        gtk_container_add (GTK_CONTAINER (popover), image_view);
        gtk_widget_show (image_view);
 
-       g_object_unref (thumbnail_slice);
+       cairo_destroy (cr);
+       cairo_surface_destroy (thumbnail_slice);
 }
 
 static gboolean
@@ -5253,7 +5261,7 @@ link_preview_job_finished_cb (EvJobThumbnail *job,
                              EvView *view)
 {
        GtkWidget *popover = view->link_preview.popover;
-       GdkPixbuf *pixbuf;
+       gint       device_scale = 1;
 
        if (ev_job_is_failed (EV_JOB (job))) {
                gtk_widget_destroy (popover);
@@ -5264,14 +5272,16 @@ link_preview_job_finished_cb (EvJobThumbnail *job,
                return;
        }
 
+#ifdef HAVE_HIDPI_SUPPORT
+        device_scale = gtk_widget_get_scale_factor (GTK_WIDGET (view));
+        cairo_surface_set_device_scale (job->thumbnail_surface, device_scale, device_scale);
+#endif
+
        if (ev_document_model_get_inverted_colors (view->model))
                ev_document_misc_invert_surface (job->thumbnail_surface);
 
-       pixbuf = ev_document_misc_pixbuf_from_surface (job->thumbnail_surface);
-
-       link_preview_show_thumbnail (pixbuf, view);
+       link_preview_show_thumbnail (job->thumbnail_surface, view);
 
-       g_object_unref (pixbuf);
        g_object_unref (job);
        view->link_preview.job = NULL;
 }