move shaders into .glsl files and add #include feature

data/shaders/comp-erase.glsl

@@ -0,0 +1,29 @@
+[[vertex]]
+uniform mat4 mvp;
+in vec4 pos;
+in vec2 uvs;
+out vec2 uv;
+void main()
+{
+    uv = uvs;
+    gl_Position = mvp * vec4(pos.xyz, 1.0);
+};
+
+[[fragment]]
+#include "include/blur.glsl"
+uniform sampler2D tex;
+uniform sampler2D tex_stroke;
+uniform sampler2D tex_mask;
+uniform mediump float alpha;
+uniform mediump float stroke_alpha;
+uniform mediump vec2 resolution;
+uniform bool mask;
+in mediump vec2 uv;
+out mediump vec4 frag;
+void main()
+{
+    mediump vec4 base = texture(tex, uv);
+    mediump vec4 stroke = texture(tex_stroke, uv);
+    stroke.a = mask ? stroke.a * stroke_alpha * blur(tex_mask, uv).r : stroke.a * stroke_alpha;
+    frag = vec4(base.rgb, clamp((base.a - stroke.a) * alpha, 0.0, 1.0));
+};