[goffice] Fix rendering on high resolution monitors when scale is not 1. [#578]

[Jean Bréfort <jbrefort src gnome org>]

commit db5cbab8f4b50208d413a34a013a3c32620f78e1
Author: Jean Brefort <jean brefort normalesup org>
Date:   Thu May 27 09:38:53 2021 +0200

    Fix rendering on high resolution monitors when scale is not 1. [#578]

 ChangeLog                  |  5 +++++
 NEWS                       |  1 +
 goffice/canvas/goc-graph.c | 31 ++++++++++++++++++++++---------
 3 files changed, 28 insertions(+), 9 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index abf12aac4..cb6b96f1d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2021-05-27  Jean Brefort  <jean brefort normalesup org>
+
+       * goffice/canvas/goc-graph.c (goc_graph_draw): fix rendering on high
+       resolution monitors when scale is not 1. #578.
+
 2021-05-12  Jean Brefort  <jean brefort normalesup org>
 
        * plugins/plot_surface/gog-matrix.c (gog_matrix_view_render): call the
diff --git a/NEWS b/NEWS
index 017c81d9c..127c1571b 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,7 @@ goffice 0.10.50:
 
 Jean:
        * Fix data update in matrix plots, see Debian #988397.
+       * Fix rendering on high resolution monitors when scale is not 1. [#578]
 
 Morten:
        * Simplify regression equation code.
diff --git a/goffice/canvas/goc-graph.c b/goffice/canvas/goc-graph.c
index ccc906417..5e6f4ce6f 100644
--- a/goffice/canvas/goc-graph.c
+++ b/goffice/canvas/goc-graph.c
@@ -186,25 +186,38 @@ goc_graph_draw (GocItem const *item, cairo_t *cr)
        GocGraph *graph = GOC_GRAPH (item);
        GocCanvas *canvas = item->canvas;
        cairo_surface_t *surf;
-       double x0, y0 = item->y0;
+       double x0, y0 = item->y0, scale = 1.;
        if (graph->renderer == NULL)
                return;
-       if (item->canvas && goc_canvas_get_direction (item->canvas) == GOC_DIRECTION_RTL) {
+       // Note that we can't have RTL when the scene has no widget, may be we can
+       // add a direction mamber to the group (in its private member) if needed
+       if (canvas && goc_canvas_get_direction (item->canvas) == GOC_DIRECTION_RTL) {
                x0 = item->x1;
                goc_group_adjust_coords (item->parent, &x0, &y0);
                x0 = canvas->width - (int) (x0 - canvas->scroll_x1) * canvas->pixels_per_unit;
        } else {
                x0 = item->x0;
                goc_group_adjust_coords (item->parent, &x0, &y0);
-               x0 = go_fake_round ((x0 - canvas->scroll_x1) * canvas->pixels_per_unit);
+               if (canvas)
+                       x0 = go_fake_round ((x0 - canvas->scroll_x1) * canvas->pixels_per_unit);
        }
        cairo_save (cr);
-       cairo_translate (cr, x0,
-                        (int) (y0 - canvas->scroll_y1) * canvas->pixels_per_unit);
-       /* scaling only there gives a better rendering, and allows for caching */
-       gog_renderer_update (graph->renderer,
-                                     go_fake_round (graph->w * canvas->pixels_per_unit),
-                                     go_fake_round (graph->h * canvas->pixels_per_unit));
+       if (canvas) {
+               cairo_translate (cr, x0,
+                                    (int) (y0 - canvas->scroll_y1) * canvas->pixels_per_unit);
+#if GTK_CHECK_VERSION(3,10,0)
+               scale = gtk_widget_get_scale_factor (GTK_WIDGET (canvas));
+               cairo_scale (cr, 1. / scale, 1. / scale);
+               /* scaling only there gives a better rendering, and allows for caching */
+               gog_renderer_update (graph->renderer,
+                                                 go_fake_round (graph->w * canvas->pixels_per_unit * scale),
+                                                 go_fake_round (graph->h * canvas->pixels_per_unit * scale));
+#endif
+       } else {
+               cairo_translate (cr, x0, y0);
+               /* scaling only there gives a better rendering, and allows for caching */
+               gog_renderer_update (graph->renderer, graph->w, graph->h);
+       }
        surf = gog_renderer_get_cairo_surface (graph->renderer);
        cairo_set_source_surface (cr, surf, 0., 0.);
        cairo_paint (cr);