Basic Rendering Tutorial

Welcome to the basic rendering tutorial for DirectX computational graphics. In this guide, we'll walk through the fundamental steps required to draw a simple triangle on the screen using DirectX 12.

1. Initialization and Device Creation

The first step is to initialize DirectX and create the necessary components, including the Direct3D device and the swap chain. The device represents the graphics hardware, and the swap chain manages the back and front buffers for rendering.

Note: Ensure you have the latest DirectX SDK installed and your development environment properly configured.

Here's a simplified C++ code snippet for device and swap chain creation:


                // Placeholder for DirectX initialization code
                Microsoft::WRL::ComPtr<ID3D12Device> m_device;
                Microsoft::WRL::ComPtr<IDXGISwapChain3> m_swapChain;

                // ... (Code to create device and swap chain) ...

2. Creating Render Targets

Render targets are the surfaces where you draw your graphics. For basic rendering, we'll create render target views (RTVs) for each buffer in the swap chain. These RTVs are used by the pipeline to know where to write the pixel data.


                // Placeholder for Render Target View creation
                std::vector<Microsoft::WRL::ComPtr<ID3D12Resource>> m_renderTargets;
                Microsoft::WRL::ComPtr<ID3D12DescriptorHeap> m_rtvHeap;

                // ... (Code to create RTVs) ...

3. Defining Vertex Data

Geometry in DirectX is defined by vertices. Each vertex typically contains position data, and optionally color, texture coordinates, or normal vectors. For our triangle, we'll define three vertices.

We'll use a simple structure to represent our vertices:


                struct Vertex {
                    float x, y, z, w; // Position
                    float r, g, b, a; // Color
                };

                // Define the triangle vertices
                std::vector<Vertex> triangleVertices = {
                    {  0.0f,  0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f }, // Top vertex (Red)
                    { -0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f }, // Bottom-left vertex (Green)
                    {  0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f }  // Bottom-right vertex (Blue)
                };

These vertices will be stored in a vertex buffer on the GPU.

4. Creating Shaders

Shaders are small programs that run on the GPU. For basic rendering, we need at least two: a Vertex Shader and a Pixel Shader.

Vertex Shader: Processes each vertex, transforming its position from model space to clip space.
Pixel Shader: Processes each pixel fragment, determining its final color.

Here are simplified HLSL (High-Level Shading Language) examples:

Vertex Shader (VS):


                struct VS_INPUT {
                    float4 pos : POSITION;
                    float4 color : COLOR;
                };

                struct PS_INPUT {
                    float4 pos : SV_POSITION;
                    float4 color : COLOR;
                };

                PS_INPUT VSMain(VS_INPUT input) {
                    PS_INPUT output;
                    output.pos = input.pos;
                    output.color = input.color;
                    return output;
                }

Pixel Shader (PS):


                float4 PSMain(PS_INPUT input) : SV_TARGET {
                    return input.color;
                }

Tip: Modern DirectX development often uses root signatures and pipeline state objects (PSOs) to manage shader stages and state.

5. Setting Up the Pipeline State Object (PSO)

The PSO encapsulates all the fixed-function and programmable states for the graphics pipeline. This includes input layout, vertex/pixel shaders, blend state, rasterizer state, and depth-stencil state.

You would create and configure a `D3D12_GRAPHICS_PIPELINE_STATE_DESC` structure and then use it to create the `ID3D12PipelineState` object.

6. The Rendering Loop

The core of rendering happens within a loop that typically executes every frame. This loop involves:

Clearing the Render Target: Resetting the render target to a background color.
Setting the Pipeline State: Binding the configured PSO.
Setting Vertex Buffers: Providing the geometry data.
Issuing Draw Commands: Telling the GPU to draw the vertices.
Presenting the Frame: Swapping the back buffer with the front buffer to display the rendered image.


                // Inside the rendering loop
                // ...
                // Clear Render Target
                // Set Pipeline State
                // Set Vertex Buffer
                // Draw primitive (e.g., draw 3 vertices for the triangle)
                // Present frame
                // ...

Conclusion

This tutorial covered the fundamental steps to achieve basic rendering with DirectX. As you progress, you'll learn about more complex topics such as 3D transformations, lighting models, texturing, and optimization techniques.