move shaders into .glsl files and add #include feature

data/shaders/stroke-instanced.glsl

@@ -0,0 +1,31 @@
+[[vertex]]
+in vec4 pos;
+in vec2 uvs;
+in mat4 a_mvp;
+in float a_flow;
+out vec3 uv;
+out float alpha;
+void main()
+{
+   uv = vec3(uvs, pos.w);
+   alpha = a_flow;
+   gl_Position = a_mvp * vec4(pos.xyz, 1.0);
+}
+
+[[fragment]]
+uniform mediump sampler2D tex;
+uniform mediump sampler2D tex_pattern;
+uniform mediump vec4 col;
+uniform mediump vec2 resolution;
+uniform mediump vec2 pattern_offset;
+uniform mediump float pattern_alpha;
+in mediump float alpha;
+in mediump vec3 uv;
+out mediump vec4 frag;
+void main()
+{
+   mediump vec2 uv2 = gl_FragCoord.st / resolution;
+   mediump float pattern = 1.0 - (texture(tex_pattern, (uv2+pattern_offset)).r * 0.9) * pattern_alpha;
+   mediump float a = (1.0 - texture(tex, uv.xy).r) * alpha * pattern;
+   frag = vec4(col.rgb, a);
+}