Step mixing gains per-sample for non-HRTF mixing

This fades the dry mixing gains using a logarithmic curve, which should produce
a smoother transition than a linear one. It functions similarly to a linear
fade except that

step = (target - current) / numsteps;
...
gain += step;

becomes

step = powf(target / current, 1.0f / numsteps);
...
gain *= step;

where 'target' and 'current' are clamped to a lower bound that is greater than
0 (which makes no sense on a logarithmic scale).

Consequently, the non-HRTF direct mixers do not do not feed into the click
removal and pending click buffers, as this per-sample fading would do an
adequate job of stopping clicks and pops caused by extreme gain changes. These
buffers should be removed shortly.

1 files changed, 7 insertions, 2 deletions

diff --git a/OpenAL32/Include/alu.h b/OpenAL32/Include/alu.h
index 3ec16565..6202c28a 100644
--- a/OpenAL32/Include/alu.h
+++ b/OpenAL32/Include/alu.h
@@ -40,7 +40,6 @@ extern "C" {
 typedef struct HrtfState {
     ALIGN(16) ALfloat History[MAX_INPUT_CHANNELS][SRC_HISTORY_LENGTH];
     ALIGN(16) ALfloat Values[MAX_INPUT_CHANNELS][HRIR_LENGTH][2];
-    ALuint Offset;
 } HrtfState;
 
 typedef struct HrtfParams {
@@ -67,12 +66,18 @@ typedef struct DirectParams {
         /* A mixing matrix. First subscript is the channel number of the input
          * data (regardless of channel configuration) and the second is the
          * channel target (eg. FrontLeft). Not used with HRTF. */
-        ALfloat Gains[MAX_INPUT_CHANNELS][MaxChannels];
+        struct {
+            ALfloat Current[MAX_INPUT_CHANNELS][MaxChannels];
+            ALfloat Step[MAX_INPUT_CHANNELS][MaxChannels];
+            ALfloat Target[MAX_INPUT_CHANNELS][MaxChannels];
+        } Gains;
     } Mix;
     /* If not 'moving', gain/coefficients are set directly without fading. */
     ALboolean Moving;
     /* Stepping counter for gain/coefficient fading. */
     ALuint Counter;
+    /* History/coefficient offset. */
+    ALuint Offset;
 
     ALfilterState LpFilter[MAX_INPUT_CHANNELS];
 } DirectParams;