Use centroid interpolation for shader lighting (fixes #4143)

files/shaders/objects_fragment.glsl

@@ -47,9 +47,9 @@ varying float depth;
 #define PER_PIXEL_LIGHTING (@normalMap || @forcePPL)
 
 #if !PER_PIXEL_LIGHTING
-varying vec4 lighting;
+centroid varying vec4 lighting;
 #else
-varying vec4 passColor;
+centroid varying vec4 passColor;
 #endif
 varying vec3 passViewPos;
 varying vec3 passNormal;

files/shaders/objects_vertex.glsl

@@ -38,9 +38,9 @@ varying float depth;
 #define PER_PIXEL_LIGHTING (@normalMap || @forcePPL)
 
 #if !PER_PIXEL_LIGHTING
-varying vec4 lighting;
+centroid varying vec4 lighting;
 #else
-varying vec4 passColor;
+centroid varying vec4 passColor;
 #endif
 varying vec3 passViewPos;
 varying vec3 passNormal;

files/shaders/terrain_fragment.glsl

@@ -17,9 +17,9 @@ varying float depth;
 #define PER_PIXEL_LIGHTING (@normalMap || @forcePPL)
 
 #if !PER_PIXEL_LIGHTING
-varying vec4 lighting;
+centroid varying vec4 lighting;
 #else
-varying vec4 passColor;
+centroid varying vec4 passColor;
 #endif
 varying vec3 passViewPos;
 varying vec3 passNormal;

files/shaders/terrain_vertex.glsl

@@ -6,9 +6,9 @@ varying float depth;
 #define PER_PIXEL_LIGHTING (@normalMap || @forcePPL)
 
 #if !PER_PIXEL_LIGHTING
-varying vec4 lighting;
+centroid varying vec4 lighting;
 #else
-varying vec4 passColor;
+centroid varying vec4 passColor;
 #endif
 varying vec3 passViewPos;
 varying vec3 passNormal;