Update

druid/materials/gui_world/gui_world.fp

@@ -0,0 +1,10 @@
+varying mediump vec2 var_texcoord0;
+varying lowp vec4 var_color;
+
+uniform lowp sampler2D texture_sampler;
+
+void main()
+{
+    lowp vec4 tex = texture2D(texture_sampler, var_texcoord0.xy);
+    gl_FragColor = tex * var_color;
+}

druid/materials/gui_world/gui_world.material

@@ -0,0 +1,8 @@
+name: "gui_world"
+tags: "tile"
+vertex_program: "/druid/materials/gui_world/gui_world.vp"
+fragment_program: "/druid/materials/gui_world/gui_world.fp"
+vertex_constants {
+  name: "view_proj"
+  type: CONSTANT_TYPE_VIEWPROJ
+}

druid/materials/gui_world/gui_world.vp

@@ -0,0 +1,16 @@
+uniform highp mat4 view_proj;
+
+// positions are in world space
+attribute highp vec3 position;
+attribute mediump vec2 texcoord0;
+attribute lowp vec4 color;
+
+varying mediump vec2 var_texcoord0;
+varying lowp vec4 var_color;
+
+void main()
+{
+    var_texcoord0 = texcoord0;
+    var_color = vec4(color.rgb * color.a, color.a);
+    gl_Position = view_proj * vec4(position.xyz, 1.0);
+}