Make use of (and require) OpenGL 4.x features present in mesa 11.0+

shaders/overlay.frag

@@ -0,0 +1,13 @@
+#version 330 core
+#extension GL_ARB_explicit_uniform_location : enable
+
+layout(location = 1) uniform sampler2D texBase;
+
+in vec2 fragTC;
+
+layout(location = 0) out vec4 color;
+
+void main(void) {
+     vec4 texCol = texture(texBase, fragTC);
+     color = texCol*texCol.w;
+}