Enguerran Cobert
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Opaax Engine

April 2025

C++ Vulkan Engine

My custom game engine (wip)

OpaaxEngine_Banner

Context

I started this project because I wanted to better understand low-level game engine programming. Until now, I mostly developed games using existing engines like Unity and Unreal Engine. This project isn’t meant to “compete” with those engines, but rather to improve my technical knowledge about how game engines work under the hood. I began by following Dave Churchill’s game engine programming course to build a strong foundation. Then, I used SFML for the graphics side and developed a small Geometry Wars–style game. After that, I added support for sprites and animations. Wanting to go deeper technically, I implemented Vulkan and moved to a modern rendering pipeline.

To keep progressing, I studied advanced resources such as:

  • Esoterica Prototype Game Engine by Bobby Anguelov
  • Enigine by furkansarihan
  • The book Game Engine Architecture by Jason Gregory

This helped me structure and build my own engine step by step.

Tech

  • Vulkan - Rendering
  • SDL - Abstracting
  • C++ - Language
  • Git - Versioning

Screenshot

Vulkan

Code

Entry point:

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#pragma once
#include "Log/OPLogMacro.h"

#ifdef OPAAX_PLATFORM_WINDOWS
extern OPAAX::OpaaxApplication* OPAAX::CreateApplication();

inline int main(int argc, char** argv)
{
	OPAAX_VERBOSE("======================= Entry point =======================")
	
	auto lApp = OPAAX::CreateApplication();
	OPAAX_LOG("[OpaaxGameEntryPoint], created Application: %1%", %typeid(*lApp).name())
	
	lApp->Initialize();
	lApp->Run();
	// lApp Shutting down it-self.
	
	delete lApp;
	return 0;
}
#else
#error Opaax Game Engine only supports Windows!
#endif

Engine flow:

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void OpaaxApplication::Initialize()
{
	OPAAX_VERBOSE("======================= Application Initialize =======================")

	//Loading base config for the engine
	OpaaxEngine::Get().LoadConfig();
	CreateInitMainWindow();
	OpaaxEngine::Get().Initialize(*m_opaaxWindow);
	
	bIsInitialize = true;
	
	OPAAX_VERBOSE("======================= Application End Initialize =======================")
}

void OpaaxApplication::Run()
{
	bIsRunning = true;
	
	while (bIsRunning)
	{
		// Handle events on queue
		SDL_Event lEvent;
		while (m_opaaxWindow->PollEvents(lEvent))
		{
			OpaaxEngine::Get().PollEvents(lEvent);
		}

		//The app will close
		if(m_opaaxWindow->ShouldClose())
		{
			//TODO Close event to make some save or other stuff
			bIsRunning = false;
			break;
		}

		if(m_opaaxWindow->IsMinimized())
		{
			//TODO Stop rendering
			//TODO Make a save?
			//std::this_thread::sleep_for(std::chrono::milliseconds(100));
		}

		OpaaxEngine::Get().PreUpdate();
		OpaaxEngine::Get().Update();
		OpaaxEngine::Get().PostUpdate();
	}
	
	Shutdown();
}

void OpaaxApplication::Shutdown()
{
	OPAAX_VERBOSE("======================= Application Shutting down =======================")
	
	bIsRunning = false;
	
	OpaaxEngine::Get().Shutdown();
	m_opaaxWindow->Shutdown();
	
	OPAAX_VERBOSE("======================= Application Shutting down End =======================")
}

Init the triangle pipepline:

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void OpaaxVulkanRenderer::InitTrianglePipeline()
{
    VkShaderModule lTriangleFragShader;

    if (!VULKAN_HELPER::LoadShaderModule("Shaders/Triangle.frag.spv", m_vkDevice, &lTriangleFragShader))
    {
        OPAAX_ERROR("Error when building the triangle fragment shader module")
    }
    else
    {
        OPAAX_LOG("Triangle fragment shader successfully loaded")
    }

    VkShaderModule lTriangleVertexShader;

    if (!VULKAN_HELPER::LoadShaderModule("Shaders/Triangle.vert.spv", m_vkDevice, &lTriangleVertexShader))
    {
        OPAAX_ERROR("Error when building the triangle vertex shader module")
    }
    else
    {
        OPAAX_LOG("Triangle vertex shader successfully loaded")
    }

    //build the pipeline layout that controls the inputs/outputs of the shader
    //we are not using descriptor sets or other systems yet, so no need to use anything other than empty default
    VkPipelineLayoutCreateInfo lPipelineLayoutInfo = VULKAN_HELPER::PipelineLayoutCreateInfo();
    VK_CHECK(vkCreatePipelineLayout(m_vkDevice, &lPipelineLayoutInfo, nullptr, &m_trianglePipelineLayout));

    OpaaxVKPipelineBuilder lPipelineBuilder;

    //use the triangle layout we created
    lPipelineBuilder.PipelineLayout = m_trianglePipelineLayout;
    //connecting the vertex and pixel shaders to the pipeline
    lPipelineBuilder.SetShaders(lTriangleVertexShader, lTriangleFragShader);
    //it will draw triangles
    lPipelineBuilder.SetInputTopology(VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST);
    //filled triangles
    lPipelineBuilder.SetPolygonMode(VK_POLYGON_MODE_FILL);
    //no backface culling
    lPipelineBuilder.SetCullMode(VK_CULL_MODE_NONE, VK_FRONT_FACE_CLOCKWISE);
    //no multisampling
    lPipelineBuilder.SetMultisamplingNone();
    //no blending
    lPipelineBuilder.DisableBlending();
    //no depth testing
    lPipelineBuilder.DisableDepthTest();

    //connect the image format we will draw into, from draw image
    lPipelineBuilder.SetColorAttachmentFormat(m_drawImage.ImageFormat);
    lPipelineBuilder.SetDepthFormat(VK_FORMAT_UNDEFINED);

    //finally build the pipeline
    m_trianglePipeline = lPipelineBuilder.BuildPipeline(m_vkDevice);

    //clean structures
    vkDestroyShaderModule(m_vkDevice, lTriangleFragShader, nullptr);
    vkDestroyShaderModule(m_vkDevice, lTriangleVertexShader, nullptr);

    m_mainDeletionQueue.PushFunction([&]()
    {
        vkDestroyPipelineLayout(m_vkDevice, m_trianglePipelineLayout, nullptr);
        vkDestroyPipeline(m_vkDevice, m_trianglePipeline, nullptr);
    });
}
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