Knowledge Base

Introduction

In the world of game development, creating realism and atmosphere is critical. A dynamic day-night cycle allows the game world to change over time, providing the player with a more immersive experience. In this article, we will examine in detail how to create a dynamic day-night cycle using C++ and DirectX9. This process involves various techniques such as changing the sky color, the movement of the sun and moon, lighting effects, and dynamically adjusting shadows. This guide is designed to appeal to both novice game developers and more experienced users.

1. Basic Concepts and Requirements

1.1 Introduction to DirectX9

DirectX9 is an API (Application Programming Interface) developed by Microsoft and widely used in game development. It provides low-level access to various system resources such as graphics processing, audio, and input devices. DirectX9 is still popular, especially on older systems, and is used in many game projects.

1.2 Required Software and Libraries

• Visual Studio: An IDE (Integrated Development Environment) for writing and compiling C++ code.
• DirectX SDK: Contains DirectX9 libraries and header files.
• Other Required Libraries: A library such as glm (OpenGL Mathematics) can be used for mathematical operations.

1.3 Basic Mathematical Knowledge

Basic knowledge of trigonometry (sine, cosine) and vector mathematics is required to create a dynamic day-night cycle. This information will be needed to calculate the position of the sun and moon, adjust lighting, and create shadows.

2. Project Setup and Basic Structure

2.1 Creating a Visual Studio Project

Create a new C++ project in Visual Studio. Remember to add the DirectX9 libraries and header files in the project settings.

2.2 Initializing DirectX9

Follow these steps to initialize DirectX9:

1. Create the IDirect3D9 interface: This interface provides access to the DirectX9 system.
2. Set the D3DPRESENT_PARAMETERS structure: This structure defines the window size, refresh rate, and other graphics settings.
3. Create the IDirect3DDevice9 interface: This interface is used to perform graphics operations.

// DirectX9 initialization example
IDirect3D9* d3d = Direct3DCreate9(D3D_SDK_VERSION);

D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory(&d3dpp, sizeof(d3dpp));
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.hDeviceWindow = hWnd; // Window handle

IDirect3DDevice9* d3dDevice;
d3d->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd,
                   D3DCREATE_SOFTWARE_VERTEXPROCESSING,
                   &d3dpp, &d3dDevice);

2.3 Game Loop

The game loop is the basic structure that allows the game to run continuously. Within this loop, input operations, game logic, and drawing operations are performed.

// Game loop example
while (isRunning) {
    // Input operations
    // Game logic
    // Drawing operations

    d3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);
    d3dDevice->BeginScene();

    // Add objects to be drawn here

    d3dDevice->EndScene();
    d3dDevice->Present(NULL, NULL, NULL, NULL);
}

3. Changing the Sky Color

3.1 Tracking Time

Use a time variable to track the progress of the day cycle. This variable will represent the different hours of the day.

// Time variable
float timeOfDay = 0.0f;

// Updating time in the game loop
timeOfDay += deltaTime; // deltaTime represents the elapsed time
if (timeOfDay > 24.0f) {
    timeOfDay -= 24.0f;
}

3.2 Color Interpolation

Define different colors corresponding to different times of the day. Then, change the sky color by interpolating between these colors (linear interpolation or more complex interpolation methods) based on the time variable.

// Color definitions
D3DCOLOR colorDawn = D3DCOLOR_XRGB(255, 150, 50);
D3DCOLOR colorNoon = D3DCOLOR_XRGB(135, 206, 235);
D3DCOLOR colorDusk = D3DCOLOR_XRGB(255, 100, 0);
D3DCOLOR colorNight = D3DCOLOR_XRGB(0, 0, 50);

// Color interpolation function (a simple example)
D3DCOLOR InterpolateColor(D3DCOLOR color1, D3DCOLOR color2, float factor) {
    float r1 = ((color1 >> 16) & 0xFF) / 255.0f;
    float g1 = ((color1 >> 8) & 0xFF) / 255.0f;
    float b1 = (color1 & 0xFF) / 255.0f;

    float r2 = ((color2 >> 16) & 0xFF) / 255.0f;
    float g2 = ((color2 >> 8) & 0xFF) / 255.0f;
    float b2 = (color2 & 0xFF) / 255.0f;

    float r = r1 + (r2 - r1) * factor;
    float g = g1 + (g2 - g1) * factor;
    float b = b1 + (b2 - b1) * factor;

    return D3DCOLOR_XRGB((int)(r * 255), (int)(g * 255), (int)(b * 255));
}

// Updating the sky color
D3DCOLOR skyColor;
if (timeOfDay > 6.0f && timeOfDay <= 12.0f) {
    skyColor = InterpolateColor(colorDawn, colorNoon, (timeOfDay - 6.0f) / 6.0f);
} else if (timeOfDay > 12.0f && timeOfDay <= 18.0f) {
    skyColor = InterpolateColor(colorNoon, colorDusk, (timeOfDay - 12.0f) / 6.0f);
} else if (timeOfDay > 18.0f && timeOfDay <= 24.0f) {
    skyColor = InterpolateColor(colorDusk, colorNight, (timeOfDay - 18.0f) / 6.0f);
} else {
    skyColor = InterpolateColor(colorNight, colorDawn, (timeOfDay / 6.0f));
}

// Setting the background color
d3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, skyColor, 1.0f, 0);

3.3 More Advanced Color Transitions

For more realistic color transitions, you can use more advanced interpolation methods such as Bezier curves or cubic splines instead of linear interpolation.

4. Movement of the Sun and Moon

4.1 Sun and Moon Models

Create simple 3D models for the sun and moon, or use ready-made models. Place these models in an appropriate location in the game world.

4.2 Orbit Calculation

Use trigonometry to calculate the orbits of the sun and moon. Update the position of the sun and moon according to the time variable. For example, you can use the following formula for the sun's orbit:

// Calculating the sun's orbit
float sunAngle = (timeOfDay / 24.0f) * 2.0f * D3DX_PI;
float sunX = cosf(sunAngle) * sunOrbitRadius;
float sunY = sinf(sunAngle) * sunOrbitRadius;

// Updating the sun's position
D3DXMATRIX sunTranslation;
D3DXMatrixTranslation(&sunTranslation, sunX, sunY, sunZ);

// Setting the sun's transformation matrix
d3dDevice->SetTransform(D3DTS_WORLD, &sunTranslation);

4.3 Lighting

Adjust the lighting according to the position of the sun and moon. Use directional light for sunlight. For moonlight, you can use a weaker directional light or ambient light.

// Setting sunlight
D3DLIGHT9 sunLight;
ZeroMemory(&sunLight, sizeof(sunLight));
sunLight.Type = D3DLIGHT_DIRECTIONAL;
sunLight.Diffuse.r = 1.0f;
sunLight.Diffuse.g = 1.0f;
sunLight.Diffuse.b = 1.0f;
sunLight.Direction.x = -sunX;
sunLight.Direction.y = -sunY;
sunLight.Direction.z = -sunZ;

d3dDevice->SetLight(0, &sunLight);
d3dDevice->LightEnable(0, TRUE);

5. Lighting and Shadows

5.1 Ambient Light

Ambient light ensures that all objects are illuminated equally. You can create a more realistic atmosphere by changing the intensity of the ambient light according to the time of day.

5.2 Directional Light

Use directional light for the sun and moon. The direction of the directional light should be adjusted according to the position of the sun and moon. A more realistic lighting can be achieved by changing the color and intensity of the directional light according to the time of day.

5.3 Shadows

Creating dynamic shadows adds depth and realism to the game world. Techniques such as shadow mapping or stencil buffer can be used to create shadows in DirectX9. Shadow mapping is a more common and performant method.

1. Creating a Depth Map: Create a depth map of the scene from the perspective of the sun or moon.
2. Applying Shadows: While drawing the scene from a normal perspective, compare each pixel with the corresponding value in the depth map. If the pixel is farther away than the value in the depth map, that pixel is in shadow.

6. Clouds and Atmosphere Effects

6.1 Cloud Layer

Adding clouds to the game world makes the atmosphere more dynamic. You can use a simple 2D texture for clouds or create more complex 3D cloud models. A simple scrolling effect can be used for the movement of clouds.

6.2 Fog Effect

The fog effect makes the game world look more realistic by hiding distant distances and adding depth to the atmosphere. To create a fog effect in DirectX9, D3DRS_FOGENABLE, D3DRS_FOGCOLOR, D3DRS_FOGSTART, and D3DRS_FOGEND render states can be used.

6.3 Atmospheric Scattering

Atmospheric scattering is an effect caused by the interaction of sunlight with particles in the atmosphere. This effect affects the color and brightness of the sky. Various mathematical models can be used to simulate the atmospheric scattering effect.

7. Performance Optimization

7.1 Reducing the Number of Objects

Reducing the number of objects in the game world is one of the most effective ways to improve performance. Remove unnecessary objects or reduce the level of detail of distant objects using LOD (Level of Detail) techniques.

7.2 Texture Optimization

Optimize the size and resolution of the textures used. Avoid using unnecessarily large textures. You can reduce the texture size by using texture compression techniques.

7.3 Reducing Draw Calls

Draw calls are an important factor that negatively affects performance. To reduce draw calls, you can use batching (drawing objects with the same material together) or instancing (drawing the same object multiple times) techniques.

7.4 Performance Monitoring Tools

You can use Visual Studio's performance monitoring tools to identify which parts of the game negatively affect performance. This information will help you direct your optimization efforts more effectively.

8. Real-Life Examples and Case Studies

Many games enhance the atmosphere and realism by using a dynamic day-night cycle. For example:

• The Elder Scrolls V: Skyrim: Skyrim offers the player a constantly changing world thanks to its dynamic day-night cycle. Sky color, lighting, and shadows change dynamically according to the time of day.
• Grand Theft Auto V: GTA V reflects the city of Los Santos in a vivid and realistic way thanks to its dynamic day-night cycle and weather effects.
• Minecraft: Although Minecraft has simple graphics, it offers the player an immersive experience thanks to its dynamic day-night cycle.

9. Frequently Asked Questions

• 9.1 Is DirectX9 still used?
• Yes, DirectX9 is still used in some projects, especially because it performs better on older systems. However, new projects generally prefer more modern APIs such as DirectX11 or DirectX12.
• 9.2 How does the dynamic day cycle affect performance?
• The dynamic day cycle can negatively affect performance, especially when it involves complex calculations such as shadows and atmospheric effects. Therefore, it is important to use various techniques to optimize performance.
• 9.3 Which interpolation method is better?
• Linear interpolation is simple and fast, but more advanced methods such as Bezier curves or cubic splines may be preferred for more realistic transitions.
• 9.4 Which technique is better for creating shadows?
• Shadow mapping is a more common and performant method than stencil buffer. However, stencil buffer may give better results in some special cases.

10. Conclusion and Summary

In this article, we examined in detail how to create a dynamic day cycle using C++ and DirectX9. We covered various techniques such as changing sky color, movement of the sun and moon, lighting effects, shadows, clouds, and atmospheric effects. We also discussed methods you can use to optimize performance.

Creating a dynamic day cycle is an effective way to add realism and atmosphere to the game world. By using the information in this article, you can create a dynamic day cycle in your own game projects and provide players with a more immersive experience.

Key Points:

• Time Tracking: Use a time variable to track the progress of the day cycle.
• Color Interpolation: Interpolate between different colors corresponding to different times of the day.
• Sun and Moon Movement: Use trigonometry to calculate the orbits of the sun and moon.
• Lighting: Adjust the lighting according to the position of the sun and moon.
• Shadows: Use shadow mapping or stencil buffer techniques to create dynamic shadows.
• Performance Optimization: Reduce the number of objects, optimize textures, and reduce draw calls.

I hope this article has helped you with creating a dynamic day cycle. Happy game development!

Additional Information

Table 1: Comparison of Lighting Types

Table 2: Comparison of Shadow Generation Techniques