Zooid Engine: First Time Profiling and Optimizing

I’ve been working on Zooid Engine (My custom game engine) since 2017. I’ve only worked on this during holidays or Sundays. Mostly, I work on stuff without really optimizing the code. About a couple of months ago, I found a real performance issue on the engine. To improve the engine, I need to focus on a couple of weekends to solve the issue. This article will be a journal of how did I do it.

Before jumping to the topic, I’d like to explain a bit about how the engine handles update and rendering.

Game Programming Journey – January & February 2020

Progress

Zooid UI

I worked on ZooidUI mostly in January. I fixed a bug where the interaction can happen when the UI component is being culled out by UI mask that I implemented in December.

I implemented a basic list view on the UI system. I tried to make this easy to use by me and other programmers. I came up with the idea to use a lambda function to create/generate UI for each item in the list view. This implementation makes each item in the listview easier to manage and customize.

ZE::UI::DoListView("ListTestWithLambda", 
		ZE::UIRect(ZE::UIVector2(0.0f, 0.0f), ZE::UIVector2(210.0f, 70.0f)), 
			listItem, 5, 
			[](const char*& text, ZE::UInt32 idx)
			{
				ZE::UI::DoText(text);
			}
		);

The function DoListView will create the list view based on the parameters. The first one is the string identifier for the list view. The second parameter is a drawing rectangle where the list view should be drawn. If the rectangle can’t have the actual content of the list view, the scroll bar will be shown. Now, It only supports vertical scrollbar. The third and the fourth parameters are a pointer to an array and the size of the array. The last parameter is the lambda function. The function should pass the reference of the data type of the array (in this case, string or char*) and the index of current item being processed. The result will look like the image below.

Game Programming Journey – November & December 2019

Progress

Zooid Engine

In October, I implemented Depth Pre-Pass into the Deferred rendering. With Depth Pre-Pass, the result can be used to make GPU occlusion queries. The queries are simply asking whether the object should be rendered or not.

How it works is by sending the draw to GPU and ask if any fragment passed. Instead of passing the model itself, passing a simple bounding box would be enough. Of course, the query can be false positive but in very rare cases (well, depending on the scene setup). Better than occluding something that should be rendered.

Besides the objects, I also implement a query for Light frustum, whether we should process the light or part of the light. The occlusion query for the light frustum helps for reducing shadow maps generation load. For example, directional light has four cascaded shadow maps based on distance from the camera. Instead of generating all four shadow maps, we can check the last three cascade shadow frustum against the scene depth. If the frustum query is failed, then we don’t need to generate the shadow maps for that frustum. Let’s say, the camera looking closely into a curtain, generating shadow maps behind the curtain is really a waste of time and the player can’t see any shadow behind the curtain anyway.

Game Programming Journey Monthly – October 2019

Progress

Zooid Engine

• Added separate draw list for rendering depth shadow map. There was some issue with shadow rendering on the engine before, which used the same draw list for drawing the actual scene. This implementation caused some problems where shadows will not be rendered in the place should be in shadow since the occluder is not part of the scene draw list. To fix this, I implemented a separate draw list for each light in the scene. The draw list is generated based on the light type.
  • Directional light will use Cascaded Shadows Map (CSM) – uses four shadow maps, and to generate draw list, it will use four orthographic frustums for each shadow map.
  • Point light uses four frustums to generate the draw list in all four directions.
  • Spotlight uses a perspective frustum to generate the draw list.
• Updated the ZooidUI code to use the latest one, along with the new update from this month. This update will include a bunch of UI components, like vector input, slider, text input box, panel, and some update on code simplicity (see ZooidUI update).
• Added support for Anisotropic filtering, also added support for OpenGL Renderer. If you see the previous update, you will notice that the texture on the floor looks blurry. Because the camera looked at the floor at the steep angle, causing the texture filtering failed (it was using trilinear filtering, I believe). I added support for enabling Anisotropic filtering on the texture object in GPU.
• Implement Depth Pre-Pass. I did read some graphics studies in the last couple of months and found out that most of them using Depth Pre-Pass (another name: Z pre-pass). This pass will help to reduce the number of fragment/pixel shader calculations in the next render pass – GBuffer pass for deferred rendering or rendering the actual scene in forward rendering. In the Depth Pre-pass, there are two passes. In the first pass, it will take only the scene to depth buffer for the first pass. In the second pass, the renderer will use the first pass’ depth buffer to render the scene and only render each pixel if the pixel passes the depth test (with compare function: less and equal than). The depth map result can also be used for GPU queries for the next pass, for example, filtering the scene draw list before sending it to the GPU (Query of drawing simple mesh – most likely box – before drawing the actual complex mesh).
• Fixed some rendering bugs:
  • Fixed frustum calculation from View Matrix;
  • Fixed bounding sphere and box for mesh that used for frustum culling;
  • Fixed frustum generation for CSM (Cascaded Shadow Map) for directional light. This fix will make the shadow frustums to fit each partition of the view frustum and improve the quality of the resulted shadow maps.

Game Programming Journey Monthly – September 2019

Progress

Zooid Engine

• Imported Crytek Sponza to the engine format. I got the Crytek Sponza scene model from McGuire Computer Graphics Archive. I still need to implement a lot of stuff in this scene: better CSM, bump mapping, and anti-aliasing.
• Improved the engine’s model parser. For the Sponza scene to be able to load in the engine, I needed to fix, modify, and add some features in the engine’s model parser.
  • There was an issue I encountered during the model parsing, mesh name issue. I used Assimp as a library to load the model. I realized the name for the mesh isn’t unique. So, when saving the result, it will override the previous mesh with a newer one.
  • Added support for scaling the model when importing.
  • Added support for creating a scene file. Assimp will break the model into several meshes. The Model Parser now will have an option to create a scene from the model file by combining all meshes into one big scene file.
  • Add support for importing material with mask texture.
• Implemented mask texture. As in the Sponza scene, it has some materials that have mask texture (like, leaf and chain).
• Added translucency pass. This pass happens after we have done with Lighting pass. Since the Deferred Rendering doesn’t fully support with any translucent object, this pass will use standard forward rendering: sort the object back to front, and render object one at a time with the light calculation.

Game Programming Journey Monthly – August 2019

This month is a really busy month for me. I had things going on almost every week. I got a small amount on time on reading books and working on my stuff. But, I managed to do some little works on my personal projects, did some small tutorials and read one rendering-related article.

Game Programming Journey Monthly – July 2019

Progress

• Zooid Engine: Implemented working SSAO (Screen-space Ambient Occlusion) in Deferred Rendering.
• Zooid Engine: Optimize GBuffer texture memory usages, set proper texture format for each GBuffer output.
• Zooid Engine: Implemented culling for spotlight and point light. If the light being culled, it will be excluded from scene lighting calculation in the scene and the shadow map will not be generated as well for that light.