Graphics Pipeline Stages
Lecture 3
Graphic Pipeline Stages:
Sequence of steps, operations that is used to
generate an image using object order
processing.
Graphic pipeline refers to a series of
interconnected stages through which data
and commands describing a scene go
through when being rendered. / produced
2 Instructor: Sadia Arshid
Graphics Pipeline(Contd…)
Application
Command
CPU
GPU
Geometry
Rasterization
Fragment
Display
3 Instructor: Sabina Irum
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Environment mapping
shadows
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Graphics Pipeline Stages
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Vertex processing
Input: vertex data (position,
color, etc.)
Output: transformed
vertices in respective object
and colors, etc.
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Vertex processing
Other geometry tasks
deformation: skinning, mesh blending
low-quality lighting
pass other properties to next stages of pipeline
the only place to algorithmically alter shape
Programmable hardware unit
algorithm can be changed at run-time by application
only recent change
7 Instructor: Sabina Irum
Clipping and rasterization
Clipping and rasterization
turns sets of vertices into
primitives and fills them in
output: set of fragments
with interpolated data
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Clipping
Remove (partial) objects not in the view frustum
efficiency: cull later stages of the pipeline
often referred as culling when full objects removed
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Rasterization
approximate primitives into pixels
pixel centered at integer coordinates
determine which pixels to turn on
no antialiasing (jaggies) pixel in the primitive
consider antialiasing for some primitives
input: vertex position in homogenous coordinates
interpolate values across primitive
colors, position at vertices
input: any vertex property
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Rasterization
required properties
uniform thickness and brightness
continuous appearance (no holes)
Efficiency
simplicity (for hardware implementation)
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Fragment processing
Fragment processing
output: final color and depth
traditionally mostly for
texture lookups
Lighting was computed for
each vertex
today, computes lighting per-
pixel
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Fragment processing
Compute final fragment colors, alphas and depth
depth is often untouched if no special effects
final lighting computations
lots of texture mapping
Texture Mapping
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Frame buffer processing
Frame buffer processing
output: final picture
hidden surface elimination
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Frame buffer processing
Hidden surface removal
sort objects back to front
draw in sorted order
does not work in many cases
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Hidden surface removal
16 Instructor: Sadia Arshid
Rendering
Rendering is the process of
generating an image from a model, by means of
computer programs.
The model is a description of three-dimensional
objects in a strictly defined language or data structure
Model would contain geometry, viewpoint, texture,
lighting, and shading information.
The image is a digital image or raster graphics image.
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Features of Rendered Image
shading — how the color and brightness of a
surface varies with lighting
texture-mapping — a method of applying detail to
surfaces
fogging/participating medium — how light dims
when passing through non-clear atmosphere or air
shadows — the effect of obstructing light
soft shadows — varying darkness caused by
partially hidden light sources
18 Instructor: Sabina Irum
Features of Rendered Image
reflection — mirror-like or highly glossy
reflection
Transparency or opacity — sharp transmission of
light through solid objects
refraction — bending of light related with
transparency
indirect illumination — surfaces illuminated by
light reflected off other surfaces, rather than
directly from a light source (also known as global
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illumination)
Instructor: Sabina Irum
Features of Rendered Image
motion blur — objects appear blurry due to
high-speed motion, or the motion of the camera
non-photorealistic rendering — rendering of
scenes in an artistic style, planned to look like a
painting or drawing
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Vertex data
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Vector processing
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Rasterization
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Fragment processing & Frame Buffer
Fragment Processing Frame Buffer (output image
in the form of pixels)
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Pipeline Stages
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