Add a corrective, click-remval sample value offset

This will hopefully be more effective and rebust at removing clicks and pops,
particularly from starts and stops in the middle of a sound. Based on an idea
by Ben Davis.

Alc/ALc.c

@@ -901,6 +901,9 @@ static ALCboolean UpdateDeviceParams(ALCdevice *device, const ALCint *attrList)
     device->SamplesPlayed += oldRate-1;
     device->SamplesPlayed /= oldRate;
 
+    for(i = 0;i < OUTPUTCHANNELS;i++)
+        device->ClickRemoval[i] = 0.0f;
+
     for(i = 0;i < device->NumContexts;i++)
     {
         ALCcontext *context = device->Contexts[i];

Alc/mixer.c

@@ -534,6 +534,7 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
 {
     float (*DryBuffer)[OUTPUTCHANNELS];
     ALfloat (*Matrix)[OUTPUTCHANNELS];
+    ALfloat *ClickRemoval;
     const ALuint *ChanMap;
     ALuint SamplesToDo;
     ALeffectslot *ALEffectSlot;
@@ -597,6 +598,16 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
         ProcessContext(NULL);
 
         //Post processing loop
+        ClickRemoval = device->ClickRemoval;
+        for(i = 0;i < SamplesToDo;i++)
+        {
+            for(c = 0;c < OUTPUTCHANNELS;c++)
+            {
+                ClickRemoval[c] -= ClickRemoval[c] / 256.0f;
+                DryBuffer[i][c] += ClickRemoval[c];
+            }
+        }
+
         ChanMap = device->DevChannels;
         Matrix = device->ChannelMatrix;
         switch(device->Format)

OpenAL32/Include/alMain.h

@@ -409,6 +409,8 @@ struct ALCdevice_struct
     ALfloat PanningLUT[OUTPUTCHANNELS * LUT_NUM];
     ALuint  NumChan;
 
+    ALfloat ClickRemoval[OUTPUTCHANNELS];
+
     // Contexts created on this device
     ALCcontext  **Contexts;
     ALuint        NumContexts;