From: Chris Bagwell <ch...@cnpbagwell.com>
There is an implied agreement between kernel drivers and
user land to work around event filtering issues. Document
our current approach since it seems not so obvious the
importance of a memset().
Our current approach works great with wacom tablets but
has some issues with non-wacom tablets. List some TODO's
to aid those developers in the future.
Also, forcing in proximity handles a few corner cases fine for
all wacom devices but document the preferred approach for
possible future patch.
Signed-off-by: Chris Bagwell <ch...@cnpbagwell.com>
---
src/wcmUSB.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 44 insertions(+), 0 deletions(-)
diff --git a/src/wcmUSB.c b/src/wcmUSB.c
index c8d775f..eed755e 100644
--- a/src/wcmUSB.c
+++ b/src/wcmUSB.c
@@ -1224,11 +1224,55 @@ static void usbDispatchEvents(InputInfoPtr pInfo)
pChannel = common->wcmChannel + channel;
dslast = pChannel->valid.state;
+ /* Because of linux input filtering, the kernel driver can not
+ * always force total set of event data when new tool comes into
+ * proximity. This includes simple case of flipping stylus
+ * from pen to eraser tool. Therefore, when new tool is in-prox
+ * we must initialize all shared event values to same as previous
+ * tool to account for filtered events.
+ *
+ * For Generic and Protocol 4 devices that have fixed channel
+ * mappings, this is no problem. Protocol 5 devices are difficult
+ * because they dynamically assign channel #'s and even simple
+ * case above can switch from channel 1 to channel 0.
+ *
+ * To simplify things, we take advantage of fact wacom kernel
+ * drivers force all values to zero when going out of proximity so
+ * we take a short cut and memset() to align when going in-prox
+ * instead of a memcpy().
+ *
+ * TODO: Some non-wacom tablets send X/Y data right before coming
+ * in proximity. The following discards that data.
+ * Adding "&& dslast.proximimty" to check would probably help
+ * this case.
+ * Some non-wacom tablets may also never reset their values
+ * to zero when out-of-prox. The memset() can loss this data.
+ * Adding a !WCM_PROTOCOL_GENERIC check would probably help this case.
+ */
if (!common->wcmChannel[channel].work.proximity)
{
memset(&common->wcmChannel[channel],0,sizeof(WacomChannel));
/* in case the in-prox event was missing */
+ /* TODO: There are not valid times when in-prox
+ * events are not sent by a driver except:
+ *
+ * 1) Starting X while tool is already in prox.
+ * 2) Non-wacom tablet sends only BTN_TOUCH without
+ * BTN_TOOL_PEN since it only support 1 tool.
+ *
+ * Case 1) should be handled in same location as
+ * below check of (ds->device_type == 0) since its
+ * same reason. It is better to query for real
+ * value instead of assuming in-prox.
+ * Case 2) should be handled in case statement that
+ * processes BTN_TOUCH for WCM_PROTOCOL_GENERIC devices.
+ *
+ * So we should not be forcing to in-prox here because
+ * it could cause cursor jump from (X,Y)=(0,0) if events
+ * are sent while out-of-prox; which can happen only
+ * with WCM_PROTOCOL_GENERIC devices. Hint: see TODO above.
+ */
common->wcmChannel[channel].work.proximity = 1;
}
--
1.7.3.1
------------------------------------------------------------------------------
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