prep for draw glow

assets/aonly.frag

@@ -0,0 +1,8 @@
+varying vec4 v_color;
+varying vec2 v_texCoords;
+uniform sampler2D u_texture;
+
+void main(void) {
+    float alpha = texture2D(u_texture, v_texCoords).a;
+    gl_FragColor = vec4(alpha, alpha, alpha, 1.0);
+}