Fix unexplained shader issue (glsl compiler bug??) (minetest#4757)

client/shaders/nodes_shader/opengl_fragment.glsl

@@ -19,6 +19,8 @@ bool normalTexturePresent = false;
 
 const float e = 2.718281828459;
 const float BS = 10.0;
+const float fogStart = 0.4;
+const float fogShadingParameter = 1 / ( 1 - fogStart);
 
 #ifdef ENABLE_TONE_MAPPING
 
@@ -199,8 +201,18 @@ void main(void)
 #endif
 
  if (fogDistance != 0.0) {
- float d = clamp((fogDistance - length(eyeVec)) / (fogDistance * 0.6), 0.0, 1.0);
- col = mix(skyBgColor, col, d);
+ // Due to a bug in some (older ?) graphics stacks (possibly in the glsl compiler ?),
+ // the fog will only be rendered correctly if the last operation before the
+ // clamp() is an addition. Else, the clamp() seems to be ignored.
+ // E.g. the following won't work:
+ // float clarity = clamp(fogShadingParameter
+ // * (fogDistance - length(eyeVec)) / fogDistance), 0.0, 1.0);
+ // As additions usually come for free following a multiplication, the new formula
+ // should be more efficient as well.
+ // Note: clarity = (1 - fogginess)
+ float clarity = clamp(fogShadingParameter
+ - fogShadingParameter * length(eyeVec) / fogDistance, 0.0, 1.0);
+ col = mix(skyBgColor, col, clarity);
  }
  col = vec4(col.rgb, base.a);
 

client/shaders/water_surface_shader/opengl_fragment.glsl

@@ -21,6 +21,8 @@ bool texSeamless = false;
 
 const float e = 2.718281828459;
 const float BS = 10.0;
+const float fogStart = 0.4;
+const float fogShadingParameter = 1 / ( 1 - fogStart);
 
 #ifdef ENABLE_TONE_MAPPING
 
@@ -155,8 +157,18 @@ vec4 base = texture2D(baseTexture, uv).rgba;
 #endif
 
  if (fogDistance != 0.0) {
- float d = clamp((fogDistance - length(eyeVec)) / (fogDistance * 0.6), 0.0, 1.0);
- col = mix(skyBgColor, col, d);
+ // Due to a bug in some (older ?) graphics stacks (possibly in the glsl compiler ?),
+ // the fog will only be rendered correctly if the last operation before the
+ // clamp() is an addition. Else, the clamp() seems to be ignored.
+ // E.g. the following won't work:
+ // float clarity = clamp(fogShadingParameter
+ // * (fogDistance - length(eyeVec)) / fogDistance), 0.0, 1.0);
+ // As additions usually come for free following a multiplication, the new formula
+ // should be more efficient as well.
+ // Note: clarity = (1 - fogginess)
+ float clarity = clamp(fogShadingParameter
+ - fogShadingParameter * length(eyeVec) / fogDistance, 0.0, 1.0);
+ col = mix(skyBgColor, col, clarity);
  }
  col = vec4(col.rgb, base.a);
 

client/shaders/wielded_shader/opengl_fragment.glsl

@@ -19,6 +19,8 @@ bool texSeamless = false;
 
 const float e = 2.718281828459;
 const float BS = 10.0;
+const float fogStart = 0.4;
+const float fogShadingParameter = 1 / ( 1 - fogStart);
 
 void get_texture_flags()
 {
@@ -107,8 +109,18 @@ void main(void)
  vec4 col = vec4(color.rgb, base.a);
  col *= gl_Color;
  if (fogDistance != 0.0) {
- float d = clamp((fogDistance - length(eyeVec)) / (fogDistance * 0.6), 0.0, 1.0);
- col = mix(skyBgColor, col, d);
+ // Due to a bug in some (older ?) graphics stacks (possibly in the glsl compiler ?),
+ // the fog will only be rendered correctly if the last operation before the
+ // clamp() is an addition. Else, the clamp() seems to be ignored.
+ // E.g. the following won't work:
+ // float clarity = clamp(fogShadingParameter
+ // * (fogDistance - length(eyeVec)) / fogDistance), 0.0, 1.0);
+ // As additions usually come for free following a multiplication, the new formula
+ // should be more efficient as well.
+ // Note: clarity = (1 - fogginess)
+ float clarity = clamp(fogShadingParameter
+ - fogShadingParameter * length(eyeVec) / fogDistance, 0.0, 1.0);
+ col = mix(skyBgColor, col, clarity);
  }
  gl_FragColor = vec4(col.rgb, base.a);
 }