load shaders from files.

vis/shaders/w-axis-hue.fs.glsl

@@ -0,0 +1,11 @@
+#version 430
+
+in vec4 vpos;
+
+out vec4 color;
+
+void main() {
+    float d = smoothstep(-2, 2, vpos.z);
+    vec3 off = 1.04 * vec3(0, 2, 4) + 2 * vec3(vpos.w);
+    color = vec4(d * cos(off), 1);
+}