[mutter] backends: Calculate output scale correctly on vertical transforms

[Carlos Garnacho <carlosg src gnome org>]

commit 70a4f599605749fc60214fb1b358984322a05137
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Jan 24 10:48:43 2017 +0100

    backends: Calculate output scale correctly on vertical transforms
    
    The code calculating the output scale involves calculations around pixel
    and mm sizes, however we do compare post-transformation pixel sizes to
    untransformed mm sizes, which breaks the DPI calculations. Fix this by
    transforming back pixel sizes back to untransformed.
    
    While we're at it, actually compare the output height to HIDPI_MIN_HEIGHT
    instead of its width, it seems right according to the #define name and
    comment.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=777687

 src/backends/native/meta-monitor-manager-kms.c |   24 +++++++++++++++++++-----
 1 files changed, 19 insertions(+), 5 deletions(-)
---
diff --git a/src/backends/native/meta-monitor-manager-kms.c b/src/backends/native/meta-monitor-manager-kms.c
index 2025676..16a04fb 100644
--- a/src/backends/native/meta-monitor-manager-kms.c
+++ b/src/backends/native/meta-monitor-manager-kms.c
@@ -498,18 +498,31 @@ find_output_by_id (MetaOutput *outputs,
 static int
 compute_scale (MetaOutput *output)
 {
-  int scale = 1;
+  int scale = 1, width, height;
 
   if (!output->crtc)
     goto out;
 
+  width = output->crtc->rect.width;
+  height = output->crtc->rect.height;
+
+  /* Swap values on rotated transforms, so pixel and mm sizes
+   * from the same axes is compared.
+   */
+  if (meta_monitor_transform_is_rotated (output->crtc->transform))
+    {
+      int tmp = width;
+      width = height;
+      height = tmp;
+    }
+
   /* Scaling makes no sense */
-  if (output->crtc->rect.width < HIDPI_MIN_HEIGHT)
+  if (height < HIDPI_MIN_HEIGHT)
     goto out;
 
   /* 4K TV */
   if (output->name != NULL && strstr(output->name, "HDMI") != NULL &&
-      output->crtc->rect.width >= SMALLEST_4K_WIDTH)
+      width >= SMALLEST_4K_WIDTH)
     goto out;
 
   /* Somebody encoded the aspect ratio (16/9 or 16/10)
@@ -523,8 +536,9 @@ compute_scale (MetaOutput *output)
   if (output->width_mm > 0 && output->height_mm > 0)
     {
       double dpi_x, dpi_y;
-      dpi_x = (double)output->crtc->rect.width / (output->width_mm / 25.4);
-      dpi_y = (double)output->crtc->rect.height / (output->height_mm / 25.4);
+
+      dpi_x = (double)width / (output->width_mm / 25.4);
+      dpi_y = (double)height / (output->height_mm / 25.4);
       /* We don't completely trust these values so both
          must be high, and never pick higher ratio than
          2 automatically */