move shaders into .glsl files and add #include feature

data/shaders/texture-blend.glsl

@@ -0,0 +1,38 @@
+[[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/ext-fb-fetch.glsl"
+#include "include/blend.glsl"
+uniform sampler2D tex;
+uniform sampler2D tex_alpha;
+uniform sampler2D tex_bg;
+uniform mediump float alpha;
+uniform int blend_mode;
+in mediump vec2 uv;
+#if defined(GL_EXT_shader_framebuffer_fetch)
+    inout highp vec4 frag;
+#else
+    out mediump vec4 frag;
+#endif
+void main() {
+#if defined(GL_EXT_shader_framebuffer_fetch)
+    highp vec4 bg = frag;
+#elif defined(GL_ARM_shader_framebuffer_fetch)
+    highp vec4 bg = gl_LastFragColorARM;
+#else
+    mediump vec4 bg = texture(tex_bg, uv);
+#endif
+    mediump vec4 fg = vec4(texture(tex, uv).rgb, texture(tex_alpha, uv).a);
+    if (fg.a == 0.0) { frag = bg; return; }
+    mediump vec4 blended = blend(bg, fg, blend_mode);
+    frag = vec4(blended.rgb, blended.a * alpha);
+};