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

1 files changed, 14 insertions, 2 deletions

diff --git a/client/shaders/nodes_shader/opengl_fragment.glsl b/client/shaders/nodes_shader/opengl_fragment.glsl
index 4d9ce1c12..149aa2bc5 100644
--- a/client/shaders/nodes_shader/opengl_fragment.glsl
+++ b/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);