Windows

The Windows tab is the first tab in the Developer UI menu. It contains various options that control different parts of the engine, from material properties to NPC behaviors. Being very useful for debugging entities and rendering, it has proven to be a great replacement for the basic console commands, making debugging faster and easier.

It consists of two windows - Addon List and Debug Menu.

Addon List

The Addon List window shows all the addons that are installed, with their name, workshop ID and absolute local path. It also shows which addons are currently mounted and which are not.

Additionally, you can mount and unmount addons by checking / unchecking addons, and then applying changes using the button at the bottom of the menu.

The Debug Menu is made to improve the debugging by reducing the amount of console usage. The menu intends to replaces commands with buttons and checkmarks that are easier and more convenient to use than console ConVars.

The debug menu consists of 5 tabs: Performance, MatSys, Renderer, Entities and AI.

Performance

The first tab has basic buttons - show host speed, FPS counter and player's position with angles.

MatSys

The second menu has options related to rendering and debugging objects, brushes, prop models, lightfaces, visleafs and more.

In P2CE, you can set mat_fullbright to 2. This draws all texture white, allowing to see exactly what lights add to the scene.

mat_bufferprimitives enables world geometry buffering. Does not draw anything on-screen, barely affects anything.
mat_wireframe draws light-blue lines on edges of each model visible and pink lines on edges of each brush with additional diagonal lines indicating faces. Use this caution, as it may cause lag when used in huge areas with lots of entities / brushes visible.
mat_luxels shows lightmaps of each lightmapped face. Each square is a light pixel. Only relevant to bakes lighting, where bigger lightmaps creates sharper shadows. Non-lightmapped faces (i.e. fizzlers) are drawn completely blue.
mat_drawflat disables normals on textures that have them, making them appear "flat". Not relevant for PBR shader.
mat_leafvis draws the visleaf the player is currently in.
mat_normals highlights normals of each face of models with tiny blue lines, and adds XYZ lines to each corner of brushes.
mat_reversedepth undraws everything, including world geometry, so basically it holds the frame the option was checked. If SSAO is enabled, a lens circle appears after some time. The image blurs when moving the camera.

Screenshots, showing each of the settings, are added below.

Map with mat_fullbright set to 2.
Map with mat_wireframe checked.
Map with mat_luxels checked.
Map with mat_leafvis checked.
Map with mat_normals checked.
Map with mat_reversedepth checked.

Renderer

The third menu consists of options related to drawing different parts of the engine.

Draw Skybox toggles the skybox. 3D skybox will disappear and 2D skybox will appear black.
Draw VGUI toggles the legacy VGUI. Obsolete since both P2CE and Momentum Mod use Panorama instead of VGUI.
Draw Panorama toggles Panorama, therefore toggling the pause menu, all the screen elements except the crosshair, and panorama_screen entities.
Draw World toggles the visibility of all brush entities and world geometry.
Draw Entities toggles the visibility of all point entities.
Draw Viewmodel toggles the visibility of the viewmodel.
Draw Static Props toggles the visibility of static props.
Draw Detail Props toggles the visibility of detail props mentioned in the .vbsp file inside the map.
Draw Model Light Origin draws green Xs at models' light origins and additionally draws 4 grey lines to each corner of models' bounding boxes.
Draw Light Info draws sprites in each light of the map. The sprites can be seen through world geometry.
Draw Decals toggles decals and overlays.
Draw Brush Models toggles the visibility of brushes that use models in any way.
Draw Area Portals toggles all the area portals in the map.
Draw Beams toggles beams created by env_laser, env_beam and beam_spotlight entities.
Draw Ropes toggles move_rope and keyframe_rope entities.
Draw Sprites toggles sprites.
Draw Particles toggles particles.
Draw Rain toggles the visibility of rain particles.
Draw Water Surface toggles water visibility. WHen inside the water, only the fog is seen.
Draw VPhysics objects toggles the visibility of objects that use VPhysics for collisions.
Draw Portal Frustum cannot be enabled as of now. It probably draws the debug lines for cameras used in portals.

Entities

The fourth menu contains buttons that draw information about the entity the player is looking at.

Show Debug Information displays the debug information of the entity as if the ent_text command was used.
Show Name displays the targetname of the entity.
Show Bounding Box shows the bounding box of the entity by drawing 8 pink lines on its edges and 4 tiny green cubes on the bottom corners of the bounding box.
Show Messages shows messages output by this entity.
Pauses freezes the entity.
Pivot draws the pivot point of the entity.

Note:

developer 1 is required to see the effects of this menu.

AI

The last, fifth menu utilizes control over the NPC entity the player is looking at.

ai_disable bypasses all AI logic routines and puts all NPCs into their idle animations.
ai_resume resumes normal processing if the NPC is stepping through tasks.
ai_stop completely disables AI for the NPC.
noclip enables noclip for the player.
god enables godmode for the player.
notarget makes enemies ignore player.

`NPC Commands` dropdown contains the following:

Enemies outputs this NPC's current entities.
Go tells the NPC to continue following its path.
Go Random tells the NPC to go in a random direction.
Route outputs this NPC's current route to their goal.
Select "selects" the NPC by drawing a dark red box around its bounding box.
Destroy removes the NPC.
Visibility tries to call a missing command called npc_visibility.
Tasks outputs this NPC's current tasks (rush, cover, heal player, etc.)
Combat sets this NPC to its combat mode.
Focus tells this NPC to focus on the target.

`Node Graph` dropdown contains the following:

Nodes displays this NPC's current nodes
Next Hull tells the NPC to move to the next cover position.
Show Hull shows this NPC's current cover position.
Show Connect shows connection of this NPC.
Show Visibility shows visibility of this NPC.
Show Graph Connect shows graph connections of this NPC.