drm/rect: Handle rounding errors in drm_rect_clip_scaled, v3.

Instead of relying on a scale which may increase rounding errors,
clip src by doing: src * (dst - clip) / dst and rounding the result
away from 1, so the new coordinates get closer to 1. We won't need
to fix up with a magic macro afterwards, because our scaling factor
will never go to the other side of 1.

Changes since v1:
- Adjust dst immediately, else drm_rect_width/height on dst gives bogus
  results.
Change since v2:
- Get rid of macros and use 64-bits math.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[mlankhorst: Add Villes comment, and rename newsrc to tmp. (Ville)]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180503112217.37292-3-maarten.lankhorst@linux.intel.com

1 files changed, 1 insertions, 2 deletions

diff --git a/include/drm/drm_rect.h b/include/drm/drm_rect.h
index 44bc122b9ee0..6c54544a4be7 100644
--- a/include/drm/drm_rect.h
+++ b/include/drm/drm_rect.h
@@ -175,8 +175,7 @@ static inline bool drm_rect_equals(const struct drm_rect *r1,
 
 bool drm_rect_intersect(struct drm_rect *r, const struct drm_rect *clip);
 bool drm_rect_clip_scaled(struct drm_rect *src, struct drm_rect *dst,
-			  const struct drm_rect *clip,
-			  int hscale, int vscale);
+			  const struct drm_rect *clip);
 int drm_rect_calc_hscale(const struct drm_rect *src,
 			 const struct drm_rect *dst,
 			 int min_hscale, int max_hscale);