Rendering is the overall process of creating a 2D image from a 3D scene, while shading is a specific part of that process focused on determining the color of objects.
According to Introduction to Shading - Scratchapixel, rendering aims to reproduce the shape, visibility, and appearance of objects as seen from a given viewpoint. This involves solving various problems, including:
- Visibility: Determining which parts of objects are visible from the camera's perspective (dealing with shape and the visibility problem).
- Appearance: Computing the color of the visible surfaces, which is where shading comes in.
Understanding Shading
Shading is specifically concerned with computing or simulating the color of objects as seen from a specific viewpoint. It deals with how light interacts with the surface properties of objects (like color, texture, reflectivity, etc.) and how that interaction affects the final color perceived by the viewer.
Key Aspects of Shading:
- Calculating how light sources illuminate surfaces.
- Determining how material properties affect reflected light.
- Considering the view direction when calculating surface color.
The Relationship: Shading as a Part of Rendering
Think of rendering as the complete pipeline from a 3D scene description to a final 2D image. Shading is a crucial step within this pipeline.
Rendering Process Steps often include:
- Scene Setup: Defining geometry, materials, lights, and camera.
- Geometry Processing: Preparing the 3D models.
- Visibility Determination: Figuring out which surfaces are visible (e.g., using z-buffer).
- Shading: Calculating the color for each visible point based on lighting and material.
- Pixel Operations: Finalizing pixel colors (e.g., alpha blending).
So, while visibility deals with which part of an object you see (shape), shading determines what color that visible part is.
Key Differences Summarized
Here's a simple comparison based on the definition provided:
| Feature | Rendering | Shading |
|---|---|---|
| Goal | Reproduce shape, visibility, and appearance of objects from a viewpoint to create a final image. | Compute or simulate the color of objects as seen from a specific viewpoint. |
| Scope | The overall process encompassing visibility, shading, and other steps. | A specific part of the rendering process focused on color calculation. |
| Concern | Shape, visibility (which parts are seen), and appearance (what color they are). | Primarily concerned with computing color based on light-matter interaction and viewpoint. |
| Reference Definition Highlight | "aims to reproduce the shape, visibility, and appearance of objects as seen from a given viewpoint." | "is concerned with computing or simulating the color of objects as seen from a specific viewpoint." |
In essence, shading is how you determine the color of the surfaces, and rendering is the broader process that uses this color information (along with shape and visibility) to produce the final image.
