drm: set a device scale of 2 on HiDPI

Using the same heuristics as gnome-settings-daemon (which ensures
that the bootsplash will be scaled if and only if the running system
is)

https://bugs.freedesktop.org/show_bug.cgi?id=84482

diff --git a/src/plugins/renderers/drm/plugin.c b/src/plugins/renderers/drm/plugin.c
index b9e5ddd69237336bd6ec339db840d186c54dff1d..49ea12563d75666f7d783c02a5e5f52556c92978 100644 (file)
--- a/src/plugins/renderers/drm/plugin.c
+++ b/src/plugins/renderers/drm/plugin.c
@@ -61,6 +61,12 @@
 
 #define BYTES_PER_PIXEL (4)
 
+/* The minimum resolution at which we turn on a device-scale of 2 */
+#define HIDPI_LIMIT 192
+#define HIDPI_MIN_HEIGHT 1200
+/* From http://en.wikipedia.org/wiki/4K_resolution#Resolutions_of_common_formats */
+#define SMALLEST_4K_WIDTH 3656
+
 struct _ply_renderer_head
 {
         ply_renderer_backend_t *backend;
@@ -391,6 +397,40 @@ ply_renderer_head_add_connector (ply_renderer_head_t *head,
         return true;
 }
 
+static int get_device_scale (uint32_t width,
+                             uint32_t height,
+                             uint32_t width_mm,
+                             uint32_t height_mm)
+{
+        int device_scale;
+        double dpi_x, dpi_y;
+
+        device_scale = 1;
+
+        if (height < HIDPI_MIN_HEIGHT)
+                return 1;
+
+        /* Somebody encoded the aspect ratio (16/9 or 16/10)
+         * instead of the physical size */
+        if ((width_mm == 160 && height_mm == 90) ||
+            (width_mm == 160 && height_mm == 100) ||
+            (width_mm == 16 && height_mm == 9) ||
+            (width_mm == 16 && height_mm == 10))
+                return 1;
+
+        if (width_mm > 0 && height_mm > 0) {
+                dpi_x = (double)width / (width_mm / 25.4);
+                dpi_y = (double)height / (height_mm / 25.4);
+                /* We don't completely trust these values so both
+                   must be high, and never pick higher ratio than
+                   2 automatically */
+                if (dpi_x > HIDPI_LIMIT && dpi_y > HIDPI_LIMIT)
+                        device_scale = 2;
+        }
+
+        return device_scale;
+}
+
 static ply_renderer_head_t *
 ply_renderer_head_new (ply_renderer_backend_t *backend,
                        drmModeConnector       *connector,
@@ -425,6 +465,11 @@ ply_renderer_head_new (ply_renderer_backend_t *backend,
         assert (ply_array_get_size (head->connector_ids) > 0);
 
         head->pixel_buffer = ply_pixel_buffer_new (head->area.width, head->area.height);
+        ply_pixel_buffer_set_device_scale (head->pixel_buffer,
+                                           get_device_scale (head->area.width,
+                                                             head->area.height,
+                                                             connector->mmWidth,
+                                                             connector->mmHeight));
 
         ply_trace ("Creating %ldx%ld renderer head", head->area.width, head->area.height);
         ply_pixel_buffer_fill_with_color (head->pixel_buffer, NULL,