Basics of 3D Rendering CS 148: Summer 2016 Introduction of Graphics - - PowerPoint PPT Presentation

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Basics of 3D Rendering CS 148: Summer 2016 Introduction of Graphics - - PowerPoint PPT Presentation

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Basics of 3D Rendering CS 148: Summer 2016 Introduction of Graphics and Imaging Zahid Hossain http://www.pling.org.uk/cs/cgv.html What We Have So Far 3D geometry 2D pipeline CS 148: Introduction to Computer Graphics and Imaging (Summer 2016)

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CS 148: Summer 2016 Introduction of Graphics and Imaging Zahid Hossain

Basics of 3D Rendering

http://www.pling.org.uk/cs/cgv.html

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What We Have So Far

3D geometry 2D pipeline

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 2

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Handy Fact

Matrices preserve flat geometry

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 3

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Handy Fact

Matrices preserve flat geometry

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 4

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So What?

3D triangles look like 2D triangles under camera transformations.

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 5

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So What?

3D triangles look like 2D triangles under camera transformations. Use 2D pipeline for 3D Rendering !

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 6

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Side Note

http://drawntothis.com/wp-content/uploads/2010/09/Random_Guy.jpg

Only true for flat shapes

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 7

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Side Note

http://drawntothis.com/wp-content/uploads/2010/09/Random_Guy.jpg

Only true for flat shapes

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 8

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Frame Buffering

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 9

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Double and Triple Buffering

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 10

Tearing : Data from multiple frames appear on the screen at the same time. This happens when GPU rendering rate and monitor refresh rate are not synced.

http://www.newcluster.com/wp-content/uploads/2015/01/g-sync_diagram_0.jpgitokgxy9kpos

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Double Buffering with V-Sync

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 11

Back Buffer Front Buffer (video memory) Front Buffer SwapBuffer: Either copy Back Buffer to Front Buffer,

  • r Swap Pointers (Usually in Fullscreen mode).

Vertical Retraces

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Double Buffering with V-Sync

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 12

Back Buffer Front Buffer (video memory) Front Buffer SwapBuffer: Either copy Back Buffer to Front Buffer,

  • r Swap Pointers (Usually in Fullscreen mode).

Vertical Retraces

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Triple Buffering with V-Sync

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 13

Front Buffer Front Buffer (Video Memory) Back Buffer 2 Vertical Retraces Back Buffer 1

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Triple Buffering with V-Sync

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 14

Front Buffer Front Buffer (Video Memory) Back Buffer 2 Vertical Retraces Back Buffer 1

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Occulusion

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Painter’s Algorithm

Draw items one at a time

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 16

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Painter’s Algorithm

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 17

Draw items one at a time

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Painter’s Algorithm

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 18

Draw items one at a time

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Painter’s Algorithm

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 19

Draw items one at a time

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Painter’s Algorithm

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 20

Draw items one at a time

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What Order?

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What Order?

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Early Hidden Surface Approaches

  • Pre-compute rendering order
  • Cut geometry as needed
  • …

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 23

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Observation

Each pixel can decide what is on top independently.

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Observation

Each pixel can decide what is on top independently.

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Z Buffer

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Color Buffer (RGB each cell) Depth buffer (one number each cell)

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Z-Buffer

http://upload.wikimedia.org/wikipedia/commons/4/4e/Z_buffer.svg

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Z-Buffer Issues: Resolution

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 28

Non linear !

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Z-Buffer Issues: Resolution

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 29

Depth

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Z-Buffer Issues: Depth Fighting

http://ps-2.kev009.com/CATIA-B18/basug_C2/basugbt1510.htm

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  • aka. “Stiching” or “bleeding”
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Z-Buffer Issues: Depth Fighting

http://ps-2.kev009.com/CATIA-B18/basug_C2/basugbt1510.htm

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 31

  • aka. “Stiching” or “bleeding”

Hack: Scale and add offset “glPolygonOffset”

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Cull [kuhl]:

To identify and throw away invisible geometry to save processing time.

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 32

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Basic Culling Strategies

  • Backface culling: remove geometry facing

away from the camera

  • View volume culling: remove geometry
  • utside frustum
  • Occlusion culling: remove invisible geometry

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 33

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Backface Culling

http://medialab.di.unipi.it/web/IUM/Waterloo/node70.html

None Backface culling Hidden surface removal

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Specifying Triangle Orientation

glFrontFace(GL_CCW)

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glDisable/glEnable(GL_CULL_FACE)

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View Volume Culling

http://i.minus.com/i75qjiyFQzVCI.jpg

Potential strategies:

  • Store scene hierarchically
  • With bounding volumes
  • Compute viewing frustrum
  • Don’t render volumes that are clearly outside frustrum

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Occlusion Culling: Portal Rendering

http://www.aaid.ca/flash/media/hkmh/images/floor1/000a-geology-portal-cg-rendering.jpg CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 37

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Occlusion Culling: Portal Rendering Potentially Visible Set

http://www.cs.virginia.edu/~luebke/publications/portals.html

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 38

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Occlusion Culling: Portal Rendering Potentially Visible Set

http://www.cs.virginia.edu/~luebke/publications/portals.html

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 39

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Occlusion Culling: Portal Rendering Potentially Visible Set (PVS)

http://www.cs.virginia.edu/~luebke/publications/portals.html

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Mirrors ?

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Summary of Culling Techniques

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Acceleration Structures

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Goal of Acceleration Structures

  • Quickly reject objects that are outside the

viewing volume

  • Query for intersections efficiently

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Spatial Hierarchies

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Letters correspond to planes (A)

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Spatial Hierarchies

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Letters correspond to planes (A,B)

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Spatial Hierarchies

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Letters correspond to planes (A,B,C,D)

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Spatial Hierarchies: Variations

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 47

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Octree

  • Each node has 0 or 8 children
  • Each node can equally subdivide its space (an AABB) into eight

subboxes by 3 midplanes

  • Children of a node are contained within the box of the node itself
  • Stop subdividing when number of objects/primitives falls below a

threshold or maximum depth has reached.

  • Recursively render cells that intersects with the viewing volume

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K-d Tree

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  • Begin with the global bounding box containing all primitives.
  • Choose an axis and a splitting plane perpendicular to that axis
  • Subdivide the primitives on both sides of the plane into two groups
  • Usually done in a balanced manner
  • Stop when the number of primitives in each single group is below a

threshold

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Shadows

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Shadows

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Shadows: Spatial Cue

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 52

http://mamassian.free.fr/papers/mamassian_tics98.pdf

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Shadows: Realism

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http://ivl.calit2.net/wiki/images/5/55/17_ShadowMappingS15.pdf

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Shadow

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 54

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Shadow

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We will only concentrate on hard-shadows

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Shadow Mapping

  • First Pass
  • Render the Scene from the light Source
  • Pretend the light is the “camera”
  • Store the depth buffer as a texture
  • Heightfield – tells us the “distance” of the nearest points from

the light source.

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Light’s POV depth map

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Shadow Mapping

  • Second Pass
  • Project the depth buffer texture from the light’s P.O.V
  • Render the scene from the camera position

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 57

Recall Projective Texturing

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Projective Texturing (RECALL)

  • Map NDC (-1 , 1 ) to Texture Coordinate space (0-1)
  • Scale and add Bias

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Final texture coordinates after perspective-correct interpolation of

Compare this with depth

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Shadow Mapping

  • Second Pass
  • Project the depth buffer texture from the light’s P.O.V
  • Render the scene from the camera position
  • Compare fragment’s depth (projected r texture

coordinate) to the depth stored in texture

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Shadow Mapping: Issues

  • Limited field of view of depth map

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Shadow Mapping: Issues

  • Limited field of view of depth map
  • Z-Fighting
  • Add scale and bias – similar to glPolygonOffset
  • Getting it right is complicated

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Shadow Mapping: Issues

  • Limited field of view of depth map
  • Z-Fighting
  • Add scale and bias – similar to glPolygonOffset
  • Getting it right is complicated
  • Sampling problem (aliasing)
  • Larger depth map may mitigate some of it

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Shadow Mapping: Issues

  • Limited field of view of depth map
  • Z-Fighting
  • Add scale and bias – similar to glPolygonOffset
  • Getting it right is complicated
  • Sampling problem (aliasing)
  • Larger depth map may mitigate some of it

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Deferred Rendering

a.k.a Deferred Shading

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 64

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Deferred Rendering

  • So far: we did Forward Rendering
  • Lots of fragments are wasted due to overdraw
  • Complex Lighting/Shading computation wasted
  • Solution: “Defer” lighting computation until we

have figured out all the pixels that end up on the screen

  • Deferred Rendering can handle lots of lights
  • Complexity:
  • Forward Rendering: Num_Objects * Num_Light
  • Deferred Rendering: Num_Object + Num_Light

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 65 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering

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Two Pass

  • 1. Geometry Pass
  • 2. Lighting Pass

http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering

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Two Pass

  • 1. Geometry Pass
  • 2. Lighting Pass

http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering

  • Transparency still done through Forward Rendering
  • Need to copy the Depth Buffer.

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 68 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering: Lots of Light

  • Can handle lots of light: key is Light Volume
  • Shade pixels that are close to a light
  • Why does not “if-else” branch work for this on the GPU?

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 69 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering: Lots of Light

  • Can handle lots of light: key is Light Volume
  • Shade pixels that are close to a light
  • Why does not “if-else” branch work for this on the GPU?
  • Draw one light volume at a time: accumulate colors

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 70 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Deferred Rendering: Lots of Light

  • Can handle lots of light: key is Light Volume
  • Shade pixels that are close to a light
  • Why does not “if-else” branch work for this on the GPU?
  • Draw one light volume at a time: accumulate colors

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 71 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

1847 Lights!

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Deferred Rendering: Challenges

  • Doesn’t support MSAA (Multiple Sample Anti-

Aliasing)

  • Extra frame buffer memory
  • Transparencies need to be done with Forward

Rendering

CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain 72 http://learnopengl.com/#!Advanced-Lighting/Deferred-Shading

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Challenges of Rasterizers

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Shadows and Reflections

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http://artist- 3d.com/free_3d_models/uploads/mantalray.jpg

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Transparencies

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http://www.archicadwiki.com/Bugs/TransparencyIn3dWindow

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Depth of Field

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http://www.seemsartless.com/guides/camera-dof-cars-fast-360.jpg

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CS 148: Summer 2016 Introduction of Graphics and Imaging Zahid Hossain

Basics of 3D Rendering

http://www.pling.org.uk/cs/cgv.html