adopting Java 9/Kotlin 1.2

assets/18BitColour.frag

@@ -0,0 +1,14 @@
+varying vec4 v_color;
+varying vec2 v_texCoords;
+uniform sampler2D u_texture;
+
+void main(void) {
+    vec4 color = texture2D(u_texture, v_texCoords).rgba;
+
+    color.r = floor(63.0 * color.r + 0.5) / 63.0;
+    color.g = floor(63.0 * color.g + 0.5) / 63.0;
+    color.b = floor(63.0 * color.b + 0.5) / 63.0;
+    // a: passthrough
+
+    gl_FragColor = vec4(color.rgb, 0.0);
+}