Vulkan & OpenGL Differences

When setting up a shaded triangle, Vulkan offers several features and concepts that are either absent or significantly different from OpenGL. Here are some key differences:

1. Explicit Control

Vulkan: Provides explicit control over GPU resources and operations. You need to manage and allocate resources like memory, command buffers, and synchronization primitives directly.
OpenGL: Abstracts much of this complexity. It handles resource management for you, making it easier for developers but less flexible for advanced use cases.

2. Command Buffers

Vulkan: Uses command buffers to record rendering commands before submitting them to the GPU. You can record commands once and execute them multiple times, allowing for better performance optimization.
OpenGL: Commands are issued immediately and not recorded for later execution. This can be less efficient, especially in complex rendering scenarios.

3. Multiple Queues

Vulkan: Supports multiple queues for different operations (graphics, compute, transfer). You can use these queues in parallel to optimize performance.
OpenGL: Generally operates on a single command queue, meaning that all rendering commands are submitted sequentially.

4. Pipeline Creation

Vulkan: Requires explicit pipeline creation for each shader stage and configuration. This process can be cumbersome but allows for fine-tuned optimization and custom behavior.
OpenGL: Simplifies pipeline management. You can bind shaders and set states with fewer API calls, which makes setup quicker and more straightforward.

5. Synchronization

Vulkan: Provides detailed synchronization control using semaphores and fences. This allows you to manage resource access and rendering operations more precisely.
OpenGL: Uses simpler synchronization mechanisms. It abstracts the synchronization process, which can lead to issues like implicit synchronization overhead.

6. Resource Binding

Vulkan: Requires explicit binding of resources (like buffers and textures) to the pipeline, which can lead to better performance through optimization.
OpenGL: Uses a more implicit model for resource binding, where resources can be bound and unbound more flexibly but can introduce overhead.

7. Shader Modules

Vulkan: Utilizes shader modules that compile GLSL (or SPIR-V) into an intermediate representation. This approach provides more control over shader compilation and linking.
OpenGL: Shaders are compiled and linked at runtime, which is easier but provides less flexibility in optimizing shader performance.

8. Render Passes

Vulkan: Uses render passes to define the structure of rendering operations, allowing for more control over how framebuffer attachments are managed and used.
OpenGL: Does not have an explicit concept of render passes; instead, it relies on simpler framebuffer attachments and operations.

Summary

Vulkan provides more control, flexibility, and optimization opportunities compared to OpenGL, but at the cost of complexity. This makes Vulkan better suited for high-performance applications, while OpenGL is often preferred for simpler applications due to its ease of use and abstraction.
If you're setting up a shaded triangle in Vulkan, you'll need to manage more details, such as command buffer creation, resource binding, and synchronization, which are mostly handled automatically by OpenGL.

+--------------------------------------+
|           OpenGL Application         |
|         (Setup and Initialization)  |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Shader Program        |
|     GLuint shaderProgram = glCreateProgram(); |
|     glAttachShader(shaderProgram, vertexShader); |
|     glAttachShader(shaderProgram, fragmentShader); |
|     glLinkProgram(shaderProgram);     |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Setup Vertex Array Object    |
|     GLuint VAO;                      |
|     glGenVertexArrays(1, &VAO);      |
|     glBindVertexArray(VAO);          |
|     glGenBuffers(1, &VBO);           |
|     glBindBuffer(GL_ARRAY_BUFFER, VBO); |
|     glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); |
|     glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0); |
|     glEnableVertexAttribArray(0);    |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|           Draw Call                 |
|     glUseProgram(shaderProgram);     |
|     glBindVertexArray(VAO);          |
|     glDrawArrays(GL_TRIANGLES, 0, 3);|
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|           Framebuffer                |
|     SwapBuffers(window);             |
+--------------------------------------+

+--------------------------------------+
|           Vulkan Application         |
|         (Setup and Initialization)  |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Instance              |
|     vkCreateInstance(&instanceInfo, &instance); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Device                |
|     vkCreateDevice(instance, &deviceCreateInfo, &device); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Shader Modules        |
|     vkCreateShaderModule(device, &vertShaderInfo, &vertShaderModule); |
|     vkCreateShaderModule(device, &fragShaderInfo, &fragShaderModule); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Graphics Pipeline      |
|     vkCreateGraphicsPipelines(device, &pipelineInfo, &pipeline); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Create Vertex Buffer         |
|     vkCreateBuffer(device, &bufferCreateInfo, &vertexBuffer); |
|     vkBindBufferMemory(device, vertexBuffer, vertexBufferMemory); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Allocate Command Buffer      |
|     vkAllocateCommandBuffers(device, &allocInfo, &commandBuffer); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Record Command Buffer        |
|     vkBeginCommandBuffer(commandBuffer, &beginInfo); |
|     vkCmdBindPipeline(commandBuffer, VK_PIPELINE_BIND_POINT_GRAPHICS, graphicsPipeline); |
|     vkCmdBindVertexBuffers(commandBuffer, 0, 1, &vertexBuffer, offsets); |
|     vkCmdDraw(commandBuffer, 3, 1, 0, 0); |
|     vkEndCommandBuffer(commandBuffer); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|         Submit Command Buffer        |
|     vkQueueSubmit(graphicsQueue, 1, &submitInfo, VK_NULL_HANDLE); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|           Render Pass                |
|      vkBeginRenderPass(commandBuffer, &renderPassInfo); |
+--------------------------------------+
                 |
                 v
+--------------------------------------+
|           Framebuffer                |
|      vkEndRenderPass(commandBuffer); |
|      vkQueuePresentKHR(presentQueue, &presentInfo); |
+--------------------------------------+