3D computer graphics work by creating a mathematical representation of a three-dimensional object or scene within a computer's memory, then projecting that representation onto a two-dimensional screen for display.
Here's a breakdown of the process:
1. 3D Modeling:
- Creation of Virtual Objects: This initial step involves building the 3D objects using specialized software. These objects are essentially collections of vertices (points in 3D space), edges (lines connecting vertices), and faces (surfaces defined by edges).
- Representing 3D Space: 3D graphics systems operate within a mathematical space, typically using a 3D Cartesian coordinate system. This system uses three axes (X, Y, and Z) to define the location of each vertex relative to an origin point.
2. 3D Rendering Pipeline:
The rendering pipeline is the core process of transforming the 3D model into a 2D image. It typically involves several stages:
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Vertex Processing: Vertices are manipulated and transformed. This includes:
- Model Transformation: Positioning and orienting the objects in the 3D scene.
- View Transformation: Defining the camera's perspective and position within the scene. This is like positioning a real-world camera to capture the scene.
- Projection Transformation: Projecting the 3D scene onto a 2D plane, creating the illusion of depth. Common projection types include perspective projection (objects appear smaller further away) and orthographic projection (no perspective).
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Rasterization: The transformed vertices are used to determine which pixels on the screen should be colored. This involves breaking down the objects into smaller fragments or pixels. Algorithms like the scanline algorithm are used to fill in the spaces between the edges of polygons.
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Fragment Processing: Each fragment (potential pixel) is processed to determine its final color. This includes:
- Shading: Calculating the color of the fragment based on lighting, material properties, and textures. Shading models like Phong shading and Blinn-Phong shading are used to simulate how light interacts with surfaces.
- Texturing: Applying images (textures) to the surfaces of the objects to add detail and realism.
- Depth Testing (Z-buffering): Determining which fragments are visible and which are hidden behind other objects. The Z-buffer stores the depth of each pixel, allowing the system to correctly draw overlapping objects.
3. Lighting and Shading:
- Simulating Light Interaction: Accurate lighting and shading are crucial for creating realistic 3D graphics. This involves simulating how light interacts with surfaces, taking into account factors such as light source position, color, intensity, and surface properties (e.g., reflectivity, roughness).
- Shading Models: Various shading models exist, each with varying levels of complexity and realism. Common models include:
- Flat Shading: Assigns a single color to each polygon, resulting in a faceted appearance.
- Gouraud Shading: Calculates the color at each vertex and interpolates the colors across the polygon, resulting in a smoother appearance than flat shading.
- Phong Shading: Calculates the normal vector at each pixel and uses it to calculate the color, resulting in the most realistic lighting effects.
4. Texturing:
- Adding Surface Detail: Texturing involves applying images or patterns to the surfaces of 3D models. This adds detail and realism without significantly increasing the complexity of the model itself.
- Texture Mapping: A technique that maps a 2D image (the texture) onto the 3D surface. This involves defining how the texture coordinates (UV coordinates) correspond to the vertices of the model.
5. Display:
- Presenting the 2D Image: The final rendered 2D image is displayed on the screen. This involves transferring the pixel data from the frame buffer (the memory area where the rendered image is stored) to the display device.
In essence, 3D computer graphics transform mathematical descriptions of 3D objects into 2D images that we can see on our screens by simulating how light interacts with these objects from a defined viewpoint.
