From f968f873beef1d5d788cc2cc0c95aaa9fa57817e Mon Sep 17 00:00:00 2001
From: Dragorn421 <Dragorn421@users.noreply.github.com>
Date: Sat, 7 Jun 2025 01:00:04 +0200
Subject: [PATCH] review

---
 src/code/z_play.c |  4 ++--
 src/code/z_rcp.c  | 20 ++++++++++----------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/code/z_play.c b/src/code/z_play.c
index b903c1f03b..7d13d7f061 100644
--- a/src/code/z_play.c
+++ b/src/code/z_play.c
@@ -225,8 +225,8 @@ void func_800BC88C(PlayState* this) {
 }
 
 /**
- * Set the default fog state controlled by the environment system.
- * If a custom fog state is used in rendering it is expected that it be reset back to this default state.
+ * Set the environment fog, from parameters controlled by the environment system.
+ * If a custom fog state is momentarily used in drawing, the environment fog is expected to be restored afterwards.
  */
 Gfx* Play_SetFog(PlayState* this, Gfx* gfx) {
     return Gfx_SetFog2(gfx, this->lightCtx.fogColor[0], this->lightCtx.fogColor[1], this->lightCtx.fogColor[2], 0,
diff --git a/src/code/z_rcp.c b/src/code/z_rcp.c
index 858ac6573f..9bfb9b6cc3 100644
--- a/src/code/z_rcp.c
+++ b/src/code/z_rcp.c
@@ -858,13 +858,13 @@ Gfx gEmptyDL[] = {
  * Set fog color and range.
  *
  * At or prior to fog near, geometry is unaffected by fog. At or beyond fog far, geometry is fully fogged.
- * Between near and far pixels will be linearly interpolated between the unfogged color and the supplied fog color.
+ * Between near and far the geometry color will be interpolated between the unfogged color and the supplied fog color.
  *
  * Fog far should be in the range 0 to 1000 and greater than or equal to fog near. If fog near is negative everything
  * will be fully fogged. If fog near is 1000 or greater there is no fog.
  */
 Gfx* Gfx_SetFog(Gfx* gfx, s32 r, s32 g, s32 b, s32 a, s32 near, s32 far) {
-    // Ensure fog far is greater than near
+    // Avoid 0 divisor in gSPFogPosition below
     if (far == near) {
         far++;
     }
@@ -874,20 +874,20 @@ Gfx* Gfx_SetFog(Gfx* gfx, s32 r, s32 g, s32 b, s32 a, s32 near, s32 far) {
     gDPSetFogColor(gfx++, r, g, b, a);
 
     if (near >= 1000) {
-        // Fog far is expected to be at most 1000 so near >= far. Set a constant shade alpha of 0 for no fog
+        // Set a constant shade alpha of 0 for no fog
         gSPFogFactor(gfx++, 0, 0);
     } else if (near > 996) {
-        // Calculating the fog multiplier when far = 1000 and near >= 997 using `128000 / (far - near)` as in
-        // SPFogPosition would result in an overflow since 128000 / (1000 - 997) > 32767. Avoid this overflow by
-        // effectively clamping near to ~996. This is almost SPFogPosition(996.0937f, 1000)
-        gSPFogFactor(gfx++, 0x7FFF, -0x7F00); // Fixed point: 0x7FFF = 1.0, -0x7F00 = -0.992
+        // Avoid an overflow when near and far are close (see bug below), by effectively clamping near to ~996.
+        // This is almost SPFogPosition(996.0937f, 1000)
+        gSPFogFactor(gfx++, 0x7FFF, -0x7F00);
     } else if (near < 0) {
-        // Fog near is out of range. Set a constant shade alpha of 255 for fully fogged
+        // Set a constant shade alpha of 255 for fully fogged
         gSPFogFactor(gfx++, 0, 255);
     } else {
         // Normal range. Shade alpha is 0 at z <= near and 255 at z >= far, linearly interpolated in between.
-        //! @bug If the difference between near and far is not at least 4, the fog multiplier will overflow. This is
-        //! handled above when fog far is 1000 but for closer fog far it is not accounted for.
+        //! @bug If far - near < 4, the computed `fm` fog factor coefficient will overflow.
+        //! For example: 128000 / (983 - 980) > 32767
+        //! This is handled above in the case of near > 996, but the general case is not accounted for.
         gSPFogPosition(gfx++, near, far);
     }
     return gfx;