[RFC] dix: Re-introduce rescaling on motion events for extended event reporting

[Magnus Vigerlöf]

Hello,

As xserver 1.4 removed the scaling callbacks for X&Y on extended
InputDevices [1], we've been forced to scale down the reported values
to the screen size. This means that we looses all the fine-grained
movement that we previously could report and for some applications this
means a loss of quality in the result for the end-user as the
applications now must work on more coarse-grained data.

Since the work to correct this is postponed for some time I propose
an interim solution where we get back the scaling so devices can
register any values on X&Y and not be tied to the changing values of
the screen size.

The patch below is tested with a Wacom tablet and works well with my
Volito 2 both as a pointer on the desktop and as a pressure-sensitive,
high-resolution pen in Gimp. At the same time my synaptic touchpad and
USB mouse worked as before.

This time I haven't introduced any interface changes. The values that
should be reported for the device are the same as in xserver 1.3,
including the max-values on X&Y. The drivers that has been adapted to
cope with the current situation will continue to work as the max-value
registered by the driver is used in the scaling.

The only worry I have with this patch is the check for if we should
scale or not. The devices I have in my system that shouldn't scale all
have '-1' as max and this is what's used to detect this situation. Is
that safe?

Comments are appreciated.

Cheers
  Magnus

[1] https://bugs.freedesktop.org/show_bug.cgi?id=10324

---
 dix/getevents.c |   54 +++++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/dix/getevents.c b/dix/getevents.c
index 6e840d4..d562e18 100644
--- a/dix/getevents.c
+++ b/dix/getevents.c
@@ -528,6 +528,7 @@ GetPointerEvents(xEvent *events, DeviceIntPtr pDev, int type, int buttons,
     DeviceIntPtr cp = inputInfo.pointer;
     int x = 0, y = 0;
     Bool coreOnly = (pDev == inputInfo.pointer);
+    ScreenPtr scr = miPointerGetScreen(pDev);
 
     /* Sanity checks. */
     if (type != MotionNotify && type != ButtonPress && type != ButtonRelease)
@@ -593,15 +594,33 @@ GetPointerEvents(xEvent *events, DeviceIntPtr pDev, int type, int buttons,
                               valuators);
 
         if (pDev->coreEvents) {
-            if (first_valuator == 0 && num_valuators >= 1)
-                x = cp->valuator->lastx + valuators[0];
+            /* Get and convert the core pointer coordinate space into
+             * device coordinates. Use the device coords if it translates
+             * into the same position as the core to preserve relative sub-
+             * pixel movements from the device. */
+            int max = pDev->valuator->axes[0].max_value;
+            if(max > 0) {
+                x = pDev->valuator->lastx;
+                if((int)((float)(x)*scr->width/(max+1)) != cp->valuator->lastx)
+                    x = (int)((float)(cp->valuator->lastx)*(max+1)/scr->width);
+            }
             else
                 x = cp->valuator->lastx;
 
-            if (first_valuator <= 1 && num_valuators >= (2 - first_valuator))
-                y = cp->valuator->lasty + valuators[1 - first_valuator];
+            max = pDev->valuator->axes[1].max_value;
+            if(max > 0) {
+                y = pDev->valuator->lasty;
+                if((int)((float)(y)*scr->height/(max+1)) != cp->valuator->lasty)
+                    y = (int)((float)(cp->valuator->lasty)*(max+1)/scr->height);
+            }
             else
                 y = cp->valuator->lasty;
+
+            /* Add relative movement */
+            if (first_valuator == 0 && num_valuators >= 1)
+                x += valuators[0];
+            if (first_valuator <= 1 && num_valuators >= (2 - first_valuator))
+                y += valuators[1 - first_valuator];
         }
         else {
             if (first_valuator == 0 && num_valuators >= 1)
@@ -620,11 +639,6 @@ GetPointerEvents(xEvent *events, DeviceIntPtr pDev, int type, int buttons,
     clipAxis(pDev, 0, &x);
     clipAxis(pDev, 1, &y);
 
-    /* This takes care of crossing screens for us, as well as clipping
-     * to the current screen.  Right now, we only have one history buffer,
-     * so we don't set this for both the device and core.*/
-    miPointerSetPosition(pDev, &x, &y, ms);
-
     /* Drop x and y back into the valuators list, if they were originally
      * present. */
     if (first_valuator == 0 && num_valuators >= 1)
@@ -634,12 +648,26 @@ GetPointerEvents(xEvent *events, DeviceIntPtr pDev, int type, int buttons,
 
     updateMotionHistory(pDev, ms, first_valuator, num_valuators, valuators);
 
+    pDev->valuator->lastx = x;
+    pDev->valuator->lasty = y;
+    /* Convert the dev coord back to screen coord if we're
+     * sending core events */
+    if (pDev->coreEvents) {
+        if(pDev->valuator->axes[0].max_value > 0)
+            x = (int)((float)(x)*scr->width/(pDev->valuator->axes[0].max_value+1));
+        if(pDev->valuator->axes[1].max_value > 0)
+            y = (int)((float)(y)*scr->height/(pDev->valuator->axes[1].max_value+1));
+    }
+
+    /* This takes care of crossing screens for us, as well as clipping
+     * to the current screen.  Right now, we only have one history buffer,
+     * so we don't set this for both the device and core.*/
+    miPointerSetPosition(pDev, &x, &y, ms);
+
     if (pDev->coreEvents) {
         cp->valuator->lastx = x;
         cp->valuator->lasty = y;
     }
-    pDev->valuator->lastx = x;
-    pDev->valuator->lasty = y;
 
     /* for some reason inputInfo.pointer does not have coreEvents set */
     if (coreOnly || pDev->coreEvents) {
@@ -677,8 +705,8 @@ GetPointerEvents(xEvent *events, DeviceIntPtr pDev, int type, int buttons,
             kbp->detail = pDev->button->map[buttons];
         }
 
-        kbp->root_x = x;
-        kbp->root_y = y;
+        kbp->root_x = pDev->valuator->lastx;
+        kbp->root_y = pDev->valuator->lasty;
 
         events++;
         if (num_valuators) {
-- 
1.5.2.5