add HairlineLayer

vtm/resources/assets/shaders/hairline.glsl

@@ -0,0 +1,39 @@
+// mali 400's fp varying has only mediump... 
+// youilabs.com/blog/mobile-gpu-floating-point-accuracy-variances/
+//  community.arm.com/groups/arm-mali-graphics/blog/2011/09/06/
+//  at-home-on-the-range--why-floating-point-formats-matter-in-graphics
+
+#ifdef GLES
+precision highp float;
+#endif
+uniform mat4 u_mvp;
+uniform vec2 u_screen;
+attribute vec2 a_pos;
+varying vec4 v_pos;
+varying vec2 s_pos;
+void
+main(){
+  v_pos = u_mvp * vec4(a_pos, 0.0, 1.0);
+  s_pos = v_pos.xy / v_pos.w;
+  gl_Position = v_pos;
+}
+
+$$
+
+#ifdef GLES
+precision highp float;
+#endif
+uniform vec4 u_color;
+uniform float u_width;
+uniform vec2 u_screen;
+varying vec4 v_pos;
+varying vec2 s_pos;
+void
+main(){
+  vec2 pos = (v_pos.xy) / v_pos.w * u_screen;
+  
+  float l = length(gl_FragCoord.xy - u_screen - pos.xy);
+  float z = clamp(0.6, 1.0, 1.2 - (v_pos.z/ v_pos.w));
+
+  gl_FragColor = u_color * (smoothstep(1.0, 0.0, l / u_width) * z);
+}