Fix T48733: World background fails in 3d-view

Missing from fix for T48555.
Unfortunately duplicates code.

source/blender/gpu/shaders/gpu_shader_vertex.glsl

@@ -14,6 +14,9 @@ varying vec3 varnormal;
 varying float gl_ClipDistance[6];
 #endif
 
+
+/* Color, keep in sync with: gpu_shader_vertex_world.glsl */
+
 float srgb_to_linearrgb(float c)
 {
 	if (c < 0.04045)
@@ -76,6 +79,9 @@ void set_var_from_attr(vec4 attr, int info, out vec4 var)
 	}
 }
 
+/* end color code */
+
+
 void main()
 {
 #ifndef USE_OPENSUBDIV

source/blender/gpu/shaders/gpu_shader_vertex_world.glsl

@@ -2,6 +2,74 @@
 varying vec3 varposition;
 varying vec3 varnormal;
 
+
+/* Color, keep in sync with: gpu_shader_vertex.glsl */
+
+float srgb_to_linearrgb(float c)
+{
+	if (c < 0.04045)
+		return (c < 0.0) ? 0.0 : c * (1.0 / 12.92);
+	else
+		return pow((c + 0.055) * (1.0 / 1.055), 2.4);
+}
+
+void srgb_to_linearrgb(vec3 col_from, out vec3 col_to)
+{
+	col_to.r = srgb_to_linearrgb(col_from.r);
+	col_to.g = srgb_to_linearrgb(col_from.g);
+	col_to.b = srgb_to_linearrgb(col_from.b);
+}
+
+void srgb_to_linearrgb(vec4 col_from, out vec4 col_to)
+{
+	col_to.r = srgb_to_linearrgb(col_from.r);
+	col_to.g = srgb_to_linearrgb(col_from.g);
+	col_to.b = srgb_to_linearrgb(col_from.b);
+	col_to.a = col_from.a;
+}
+
+bool is_srgb(int info)
+{
+#ifdef USE_NEW_SHADING
+	return (info == 1)? true: false;
+#else
+	return false;
+#endif
+}
+
+void set_var_from_attr(float attr, int info, out float var)
+{
+	var = attr;
+}
+
+void set_var_from_attr(vec2 attr, int info, out vec2 var)
+{
+	var = attr;
+}
+
+void set_var_from_attr(vec3 attr, int info, out vec3 var)
+{
+	if (is_srgb(info)) {
+		srgb_to_linearrgb(attr, var);
+	}
+	else {
+		var = attr;
+	}
+}
+
+void set_var_from_attr(vec4 attr, int info, out vec4 var)
+{
+	if (is_srgb(info)) {
+		srgb_to_linearrgb(attr, var);
+	}
+	else {
+		var = attr;
+	}
+}
+
+/* end color code */
+
+
 void main()
 {
 	/* position does not need to be transformed, we already have it */