merged all drawing functions into a single shader processing function

app/shaders/default.frag

@@ -15,7 +15,6 @@ in vec2 ove_texcoord;
 out vec4 fragColor;
 
 void main() {
-    vec2 using_texcoord = ove_texcoord;
     vec4 color = texture(ove_maintex, ove_texcoord);
     fragColor = color;
-}
+}