1. 2. The Graphics Rendering Pipeline
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Real-time Rendering
2. The Graphics Rendering Pipeline

2. Graphics Rendering Pipeline
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Graphics Rendering Pipeline
The main function of the pipeline
To generate (render) a 2D image
Given virtual camera, 3D objects, light source, lighting models, textures, and more
The underlying tool for RT rendering

3. Architecture (1/3) The speed of pipeline Real-time rendering pipeline
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Architecture (1/3)
The speed of pipeline
Determined by its slowest pipeline stage
1 Stage  2 Stage  3 Stage  …  n Stage
Bottleneck
Real-time rendering pipeline
Three conceptual stage

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Architecture (2/3)
Difference between conceptual, functional and pipeline stages
Functional stage has a certain task to perform
A pipeline stage is executed simultaneously with all the other pipeline stages
Example
The geometry stage may be divided into 5 functional stages
May combine 2 functional stage into one pipeline stage
divides another functional stage into several pipeline stage
Even parallelizes it

5. Architecture (3/3) Rendering Speed (Throughput)
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Architecture (3/3)
Rendering Speed (Throughput)
The update speed of the images
Frame per second or Hz (1/second)
Example
Output device’s maximum update frequency : 60 Hz
Bottleneck of rendering pipeline : 62.5 ms
Rendering speed ?

6. The Application Stage Application Stage Software- based implementation
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The Application Stage
Application Stage
Software- based implementation
The developer has full control
Not divided into sub-stages
Could be executed in parallel on several processors in order to increase performance
The geometry to be rendered is fed to the next stage in the rendering pipeline
Collision Detection, Acceleration Algorithms, Animations, Geometry morphing, Force feedback

7. The Geometry Stage (1/6) Divided into 5 functional stages
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The Geometry Stage (1/6)
Divided into 5 functional stages

8. The Geometry Stage (2/6) Model and View Transform
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The Geometry Stage (2/6)
Model and View Transform
Model resides in its own model space
Model transform : Several copies (instances)
Model Coordinates  World Coordinates
View transform
Place camera at the origin
make it look in the direction of the negative z-axis, with the y-axis pointing upwards and the x-axis pointing to the right

9. The Geometry Stage (3/6) Lighting and Shading Lighting equation
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The Geometry Stage (3/6)
Lighting and Shading
Lighting equation
Real-world interaction between photons and surfaces.
Not much time can be spent on simulating this phenomenon
Gouraud shading
Compute a color at each vertex of the surface
Location of light sources and their properties
The position and the normal of the vertex
The properties of the material belong to the vertex
Then interpolated over triangle

10. The Geometry Stage (4/6) Projection
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The Geometry Stage (4/6)
Projection
Transforms the view volume into a unit cube(= canonical view volume)
with its extreme points at (-1, -1, -1) and (1, 1, 1)
Orthographics (=parallel) projection
Parallel lines remain parallel after the transform
The combination of a translation and a scaling
Perspective projection
Parallel line may converge at the horizon
Frustum
A truncated pyramid with rectangular base
Project from three to two dimension

11. The Geometry Stage (5/6) Clipping Primitives
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The Geometry Stage (5/6)
Clipping
Primitives
totally inside view volume  pass the next stage
totally outside view volume  not pass the next stage
Partially inside view volume  clipping

12. The Geometry Stage (6/6) Screen Mapping
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The Geometry Stage (6/6)
Screen Mapping
Transform to form the screen coordinates
window coordinate
Screen coordinates together with the z-coordinates

13. The Rasterizer Stage (1/2)
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The Rasterizer Stage (1/2)
The goal of the rasterizer Stage
Rasterization (= scan conversion)
Assign correct colors to pixels to render an image correctly
Geometry stage  per polygon operation
Rasterizer stage  per pixel operation
The information for each pixel
Color buffer (R, G, B)
Double buffering ( front buffer back buffer)
Responsible for resolving visibility
Z-buffer (=Depth buffer)
Same size and shape as the color buffer
Stores the z-value from the camera to the closest primitive
New z value < Z-buffer z value  update color and z value
New z value > Z-buffer z value  untouched

14. The Rasterizer Stage (2/2)
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The Rasterizer Stage (2/2)
Texturing
Increase the level of realism
Gluing an image onto the object
Alpha channel
Associated with the color buffer
Stores a related opacity value for each pixel
Stencil buffer
Usually contains from one to eight bits per pixel
A powerful tool for generating special effects
Frame buffer
Consists of all the buffers on the system
In 1990, Haeberli and Akeley
Accumulation buffer
Accumulated using a set of operators.
Generate motion blur, depth of field, antialiasing, soft shadow, etc