Discard small alpha values in fragment shader

src/shaders/default.frag

@@ -83,6 +83,11 @@ vec3 calculate_spot_light(SpotLight light, vec3 normal, vec3 frag_position, vec3
 
 void main()
 {
+    vec4 texture_color = texture(u_material.diffuse, texture_coords);
+    if (texture_color.a < 1e-2) {
+        discard;
+    }
+
     vec3 norm = normalize(normal);
 
     vec3 view_pos = vec3(inverse(view)[3]);