Bindings: Zero controls when receiving conflicting input

Added cvar "input-conflict-zerocontrol" (default: 1) that causes
controls that are being simultaneously affected by more than one
device states from the same input device to be cleared to zero.

This corrects a behavioral compatibility issue where holding down
a turn key when already turning to the other direction would cause
the control position to first go through the half-speed stage
before zeroing.

Another possible solution to address this issue would be to track
staging per control rather than per input device state (i.e., now
there is a timer for each key of the keyboard and none for the
control itself), but implementing that would be too much work
during Candidate phase. It should be done at a later time, though.

doomsday/engine/data/cphelp.txt

@@ -957,6 +957,9 @@ desc = Maximum limit for the frame rate (default: 200).
 [input-toggle-sharp]
 desc = 1=Process toggle events only on sharp ticks for backwards compatible behavior.
 
+[input-conflict-zerocontrol]
+desc = 1=If a control is influenced by two or more conflicting input device states, the control position gets zeroed.
+
 [input-key-delay1]
 desc = The number of milliseconds to wait before first key repeat.
 

doomsday/engine/portable/include/b_device.h

@@ -34,7 +34,8 @@
 typedef enum cbdevtype_e {
     CBD_TOGGLE,
     CBD_AXIS,
-    CBD_ANGLE
+    CBD_ANGLE,
+    NUM_CBD_TYPES
 } cbdevtype_t;
 
 // Flags for control-device bindings.

doomsday/engine/portable/src/b_device.c

@@ -55,6 +55,7 @@
 
 float       stageThreshold = 6.f/35;
 float       stageFactor = .5f;
+byte        zeroControlUponConflict = true;
 
 // PRIVATE DATA DEFINITIONS ------------------------------------------------
 
@@ -288,6 +289,8 @@ void B_EvaluateDeviceBindingList(int localNum, dbinding_t* listRoot, float* pos,
     float       deviceOffset;
     uint        deviceTime;
     uint        nowTime = Sys_GetRealTime();
+    boolean     conflicted[NUM_CBD_TYPES] = { false, false, false };
+    boolean     appliedState[NUM_CBD_TYPES] = { false, false, false };
 
     *pos = 0;
     *relativeOffset = 0;
@@ -397,6 +400,26 @@ void B_EvaluateDeviceBindingList(int localNum, dbinding_t* listRoot, float* pos,
 
         *pos += devicePos;
         *relativeOffset += deviceOffset;
+
+        // Is this state contributing to the outcome?
+        if(!FEQUAL(devicePos, 0.f))
+        {
+            if(appliedState[cb->type])
+            {
+                // Another binding already influenced this; we have a conflict.
+                conflicted[cb->type] = true;
+            }
+
+            // We've found one effective binding that influences this control.
+            appliedState[cb->type] = true;
+        }
+    }
+
+    if(zeroControlUponConflict)
+    {
+        for(i = 0; i < NUM_CBD_TYPES; ++i)
+            if(conflicted[i])
+                *pos = 0;
     }
 
     // Clamp appropriately.

doomsday/engine/portable/src/b_main.c

@@ -154,6 +154,10 @@ static const keyname_t keyNames[] = {
 
 void B_Register(void)
 {
+    extern byte zeroControlUponConflict;
+
+    C_VAR_BYTE("input-conflict-zerocontrol", &zeroControlUponConflict, 0, 0, 1);
+
 #define PROTECTED_FLAGS     (CMDF_NO_DEDICATED|CMDF_DED|CMDF_CLIENT)
 
     C_CMD_FLAGS("bindevent",      "ss",   BindEventToCommand, PROTECTED_FLAGS);