layer highlight when selected

engine/app_shaders.cpp

@@ -38,10 +38,14 @@ void App::initShaders()
         SHADER_VERSION
         "uniform sampler2D tex;\n"
         "uniform mediump float alpha;\n"
+        "uniform bool highlight;\n"
         "in mediump vec3 uv;\n"
         "out mediump vec4 frag;\n"
         "void main(){\n"
-        "   frag = texture(tex, uv.xy) * vec4(1,1,1,alpha);\n"
+        "   mediump vec4 c = texture(tex, uv.xy);\n"
+        "   frag = highlight ? \n"
+        "       vec4(clamp(vec3(.3)+c.rgb, vec3(0), vec3(1)), c.a) : \n"
+        "       texture(tex, uv.xy) * vec4(1,1,1,alpha);\n"
         "}\n";
     // TEXTURE COMP ERASE
     static const char* shader_comp_erase_f =