implement F3xx and F4xx for fine vol slides

papers/doc/3-pattern/effects.md

@@ -54,6 +54,8 @@ however, effects are continuous, which means you only need to type it once and t
 - `F0xx`: change song Hz by BPM value.
 - `F1xx`: single tick slide up.
 - `F2xx`: single tick slide down.
+- `F3xx`: fine volume slide up (64x slower than `0Axy`).
+- `F4xx`: fine volume slide down (64x slower than `0Axy`).
 - `F8xx`: single tick volume slide up.
 - `F9xx`: single tick volume slide down.
 - `FAxy`: fast volume slide (4x faster than `0Axy`).

src/engine/engine.cpp

@@ -104,6 +104,10 @@ const char* DivEngine::getEffectDesc(unsigned char effect, int chan) {
       return "F1xx: Single tick note slide up";
     case 0xf2:
       return "F2xx: Single tick note slide down";
+    case 0xf3:
+      return "F3xx: Fine volume slide up";
+    case 0xf4:
+      return "F4xx: Fine volume slide down";
     case 0xf8:
       return "F8xx: Single tick volume slide up";
     case 0xf9:

src/gui/pattern.cpp

@@ -65,8 +65,8 @@ const FurnaceGUIColors extFxColors[32]={
   GUI_COLOR_PATTERN_EFFECT_SPEED, // F0
   GUI_COLOR_PATTERN_EFFECT_PITCH, // F1
   GUI_COLOR_PATTERN_EFFECT_PITCH, // F2
-  GUI_COLOR_PATTERN_EFFECT_INVALID, // F3
-  GUI_COLOR_PATTERN_EFFECT_INVALID, // F4
+  GUI_COLOR_PATTERN_EFFECT_VOLUME, // F3
+  GUI_COLOR_PATTERN_EFFECT_VOLUME, // F4
   GUI_COLOR_PATTERN_EFFECT_INVALID, // F5
   GUI_COLOR_PATTERN_EFFECT_INVALID, // F6
   GUI_COLOR_PATTERN_EFFECT_INVALID, // F7