[PATCH] dix: pre-scale x by the screen:device:resolution ratio

[Peter Hutterer]

commit 61a99aff9d33728a0b67920254d2d4d79f80cf39
    dix: pre-scale relative events from abs devices to desktop ratio (#31636)

added pre-scaling of relative coordinates coming from absolute devices to
undo uneven scaling based on the screen dimensions.

Devices have their own device width/height ratio as well (in a specific
resolution) and this must be applied for relative devices as well to avoid
scaling of the relative events into the device's ratio.

e.g. a Wacom Intuos4 6x9 is in 16:10 format with equal horiz/vert
resolution (dpi). A movement by 1000/1000 coordinates is a perfect diagonal
on the tablet and must be reflected as such on the screen.

However, we map the relative device-coordinate events to absolute screen
coordinates based on the axis ranges. This results in an effective scaling
of 1000/(1000 * 1.6) and thus an uneven x/y axis movement - the y
axis is always faster.

So we need to pre-scale not only by the desktop dimenstions but also by the
device width/height ratio _and_ the resolution ratio.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
 dix/getevents.c | 46 ++++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/dix/getevents.c b/dix/getevents.c
index a4f192c..bb2f174 100644
--- a/dix/getevents.c
+++ b/dix/getevents.c
@@ -769,6 +769,29 @@ add_to_scroll_valuator(DeviceIntPtr dev, ValuatorMask *mask, int valuator, doubl
 }
 
 
+static void
+scale_for_device_resolution(DeviceIntPtr dev, ValuatorMask *mask)
+{
+    double x;
+    ValuatorClassPtr v = dev->valuator;
+    int xrange = v->axes[0].max_value - v->axes[0].min_value + 1;
+    int yrange = v->axes[1].max_value - v->axes[1].min_value + 1;
+
+    double screen_ratio = 1.0 * screenInfo.width/screenInfo.height;
+    double device_ratio = 1.0 * xrange/yrange;
+    double resolution_ratio = 1.0;
+    double ratio;
+
+    if (!valuator_mask_fetch_double(mask, 0, &x))
+        return;
+
+    if (v->axes[0].resolution != 0 && v->axes[1].resolution != 0)
+        resolution_ratio = 1.0 * v->axes[0].resolution/v->axes[1].resolution;
+
+    ratio = device_ratio/resolution_ratio/screen_ratio;
+    valuator_mask_set_double(mask, 0, x * ratio);
+}
+
 /**
  * Move the device's pointer by the values given in @valuators.
  *
@@ -780,27 +803,14 @@ moveRelative(DeviceIntPtr dev, int flags, ValuatorMask *mask)
 {
     int i;
     Bool clip_xy = IsMaster(dev) || !IsFloating(dev);
+    ValuatorClassPtr v = dev->valuator;
 
     /* for abs devices in relative mode, we've just scaled wrong, since we
        mapped the device's shape into the screen shape. Undo this. */
-    if ((flags & POINTER_ABSOLUTE) == 0 && dev->valuator &&
-        dev->valuator->axes[0].min_value < dev->valuator->axes[0].max_value) {
-
-        double ratio = 1.0 * screenInfo.width/screenInfo.height;
-
-        if (ratio > 1.0) {
-            double y;
-            if (valuator_mask_fetch_double(mask, 1, &y)) {
-                y *= ratio;
-                valuator_mask_set_double(mask, 1, y);
-            }
-        } else {
-            double x;
-            if (valuator_mask_fetch_double(mask, 0, &x)) {
-                x *= ratio;
-                valuator_mask_set_double(mask, 0, x);
-            }
-        }
+    if ((flags & POINTER_ABSOLUTE) == 0 && v && v->numAxes > 1 &&
+        v->axes[0].min_value < v->axes[0].max_value &&
+        v->axes[1].min_value < v->axes[1].max_value) {
+        scale_for_device_resolution(dev, mask);
     }
 
     /* calc other axes, clip, drop back into valuators */
-- 
1.8.1.4