Rendering Pipeline - Computer Graphics, Exams of Computer Graphics

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Image Processing and Computer Graphics

Rendering Pipeline

Matthias Teschner

Computer Science Department

University of Freiburg

 introduction

 rendering pipeline

 vertex processing

 primitive processing

 fragment processing

 summary

Outline

 rendering algorithm for generating 2D images from

3D scenes

 transforming geometric primitives such as lines and

polygons into raster image representations, i.e. pixels

Rasterization

[Akenine-Moeller et al.: Real-time Rendering]

 3D objects are approximately represented by

vertices (points), lines, polygons

 these primitives are processed to obtain a 2D image

Rasterization

[Akenine-Moeller]

 introduction

 rendering pipeline

 vertex processing

 primitive processing

 fragment processing

 summary

Outline

 3D input

 a virtual camera

 position, orientation, focal length

 objects

 points (vertex / vertices), lines, polygons

 geometry and material properties

(position, normal, color, texture coordinates)

 light sources

 direction, position, color, intensity

 textures (images)

 2D output

 per-pixel color values in the framebuffer

Rendering Pipeline - Task

Rendering Pipeline Main Stages  vertex processing / geometry stage / vertex shader  processes all vertices independently in the same way  performs transformations per vertex, computes lighting per vertex  geometry shader  generates, modifies, discards primitives  primitive assembly and rasterization / rasterization stage  assembles primitives such as points, lines, triangles  converts primitives into a raster image  generates fragments / pixel candidates  fragment attributes are interpolated from vertices of a primitive  fragment processing / fragment shader  processes all fragments independently in the same way  fragments are processed, discarded or stored in the framebuffer

Rendering Pipeline Main Stages

[Lighthouse 3D]

 vertex position transform  lighting per vertex  primitive assembly, combine vertices to lines, polygons  rasterization, computes pixel positions affected by a primitive  fragment generation with interpolated attributes, e.g. color  fragment processing (not illustrated), fragment is discarded or used to update the pixel information in the framebuffer, more than one fragment can be processed per pixel position

 introduction

 rendering pipeline

 vertex processing

 primitive processing

 fragment processing

 summary

Outline

 model transform  view transform  lighting  projection transform  clipping  viewport transform Vertex Processing (Geometry Stage)

 M 1 , M 2 , M 3 , M 4 , V are matrices representing transformations

 M 1 , M 2 , M 3 , M 4 are model transforms to place the objects in the scene

 V places and orientates the camera in space

 V

• 1

transforms the camera to the origin looking along the negative z-axis

 model and view transforms are combined in the modelview transform

 the modelview transform V

• 1

M1..4 is applied to the objects

Model Transform View Transform

V

• 1

[Akenine-Moeller et al.: Real-time Rendering]

M 1

M 3 M 2

M 4

V

Inverse

 interaction of light sources and surfaces

is represented with a lighting /

illumination model

 lighting computes color for each vertex

 based on light source positions and properties

 based on transformed position, transformed

normal, and material properties of a vertex

Lighting

 view volume (cuboid or frustum) is transformed

into a cube (canonical view volume)

 objects inside (and outside) the view volume

are transformed accordingly

 orthographic

 combination of translation and scaling

 all objects are translated and scaled in the same way

 perspective

 complex transformation

 scaling factor depends on the distance of an object to the viewer

 objects farther away from the camera appear smaller

Projection Transform

 primitives, that intersect the boundary of the view

volume, are clipped

 primitives, that are inside, are passed to the next processing stage

 primitives, that are outside, are discarded

 clipping deletes and generates vertices and primitives

Clipping

[Akenine-Moeller et al.: Real-time Rendering]