utils: Add ply_guess_device_scale () helper

Add a ply_guess_device_scale () helper for getting device-scale
when the physical dimensions of the output are not available.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

2 files changed, 36 insertions, 5 deletions

diff --git a/src/libply/ply-utils.c b/src/libply/ply-utils.c
index ed6b054a..fb77e74b 100644
--- a/src/libply/ply-utils.c
+++ b/src/libply/ply-utils.c
@@ -868,12 +868,20 @@ ply_set_device_scale (int device_scale)
 /* The minimum resolution at which we turn on a device-scale of 2 */
 #define HIDPI_LIMIT 192
 #define HIDPI_MIN_HEIGHT 1200
+#define HIDPI_MIN_WIDTH 2560 /* For heuristic / guessed device-scale */
 
-int
-ply_get_device_scale (uint32_t width,
-                      uint32_t height,
-                      uint32_t width_mm,
-                      uint32_t height_mm)
+/*
+ * If we have guessed the scale once, keep guessing to avoid
+ * changing the scale on simpledrm -> native driver switch.
+ */
+static bool guess_device_scale;
+
+static int
+get_device_scale (uint32_t width,
+                  uint32_t height,
+                  uint32_t width_mm,
+                  uint32_t height_mm,
+                  bool     guess)
 {
         int device_scale;
         double dpi_x, dpi_y;
@@ -890,6 +898,9 @@ ply_get_device_scale (uint32_t width,
         if (height < HIDPI_MIN_HEIGHT)
                 return 1;
 
+        if (guess)
+                return (width >= HIDPI_MIN_WIDTH) ? 2 : 1;
+
         /* Somebody encoded the aspect ratio (16/9 or 16/10)
          * instead of the physical size */
         if ((width_mm == 160 && height_mm == 90) ||
@@ -911,6 +922,23 @@ ply_get_device_scale (uint32_t width,
         return device_scale;
 }
 
+int
+ply_get_device_scale (uint32_t width,
+                      uint32_t height,
+                      uint32_t width_mm,
+                      uint32_t height_mm)
+{
+        return get_device_scale (width, height, width_mm, height_mm,
+                                 guess_device_scale);
+}
+
+int ply_guess_device_scale (uint32_t width,
+                            uint32_t height)
+{
+        guess_device_scale = true;
+        return get_device_scale (width, height, 0, 0, true);
+}
+
 static const char *
 ply_get_kernel_command_line (void)
 {
diff --git a/src/libply/ply-utils.h b/src/libply/ply-utils.h
index 09507e09..3893a6f6 100644
--- a/src/libply/ply-utils.h
+++ b/src/libply/ply-utils.h
@@ -127,6 +127,9 @@ int ply_get_device_scale (uint32_t width,
                           uint32_t width_mm,
                           uint32_t height_mm);
 
+int ply_guess_device_scale (uint32_t width,
+                            uint32_t height);
+
 const char *ply_kernel_command_line_get_string_after_prefix (const char *prefix);
 bool ply_kernel_command_line_has_argument (const char *argument);
 void ply_kernel_command_line_override (const char *command_line);