Depth Cues
"Hints" that suggest three-dimensionality - shape or distance
Based on physics, and workings of human vision
Occlusion / Interposition
Limbourg. Très Riches Heures: January. 1412-16
Occlusion / Interposition
Hiroshige. Plum Estate, Kameido. 1857
Occlusion / Interposition
Diablo
Perspective
- Linear Perspective
- Relative Size
- Relative Height
- Texture Gradient
Linear Perspective
van Gogh. Corridor in the Asylum. 1889
Linear Perspective
Dalí. The Fist Days of Spring 1932
Linear Perspective
Tempest
Relative Size
Durer. The Adoration of the Magi. 1504
Relative Size
Monet. Wheatstacks (End of Summer), 1890-91
Relative Size
Wolfenstein 3D
Relative Height
Limbourg. Très Riches Heures: February. 1412-16
Relative Height
Constable. Chain Pier, Brighton. 1827
Relative Height
QBert
Texture Gradient
Botticelli. The Birth of Venus. c. 1485-86
Texture Gradient
Hockney. A Lawn Being Sprinkled. 1967
Texture Gradient
Hockney. A Lawn Being Sprinkled (detail)
Texture Gradient
Lighting & Shadows
Michelangelo. David. 1504
Lighting & Shadows
Michelangelo. The Holy Family with the infant St. John the Baptist (the Doni Tondo). c. 1503-05
Lighting & Shadows
Monet. Rouen Cathedral, the West Portal and Saint-Romain Tower, Full Sunlight, Harmony in Blue and Gold) / Rouen Cathedral: Full Sunlight. 1894
Lighting & Shadows
Mario 64 / Doom 3
Aerial Perspective
Friedrich. Riesengebirge. 1835
Aerial Perspective
Monet. The Thames at Westminster (Westminster Bridge). 1871
Aerial Perspective
Grand Theft Auto 3
Accomodation (Focus)
Vermeer. The Lacemaker. 1669-70
Accomodation (Focus)
Wyler. The Little Foxes. 1941
Accomodation (Focus)
Motion Parallax
Disner. The Old Mill. 1937
Motion Parallax
Shadow of the Beast
Stereo Parallax
Stereo Parallax
Stereo Parallax
Virtual Boy - Mario's Tennis
Summary
- occlusion
- linear perspective
- relative size
- relative height
- texture gradient
- shading, shadows
- aerial perspective
- accomodation
- stereo parallax
- motion parallax
OpenGL
- occlusion
- depth-buffering (glEnable(GL_DEPTH_TEST))
- linear perspective
- relative size
- relative height
- perspective projection (gluPerspective)
- texture gradient
- perspective, texture mapping (glTexImage2D, etc)
- shading, shadows
- lighting (glLight, glMaterial, glNormal)
- aerial perspective
- fog (glFog)
- accomodation
- accumulation buffer (glAccum)
- stereo parallax
- quad-buffering, color-masking
- motion parallax
- transformations
Hidden Surfaces
Hidden surfaces provide occlusion depth cue
Hidden Surface Algorithms
Many different algorithms developed over the years
- Painter's algorithm
- must sort everything from back to front
- Binary Space Partition (BSP) tree
- Ray-casting
- Depth buffering
(aka Z buffering)
- etc
Depth Buffering
Rendering a polygon means filling pixels
Color buffer contains RGB color of each pixel drawn
Depth buffer contains depth of each pixel drawn
| Color | Depth |
|---|
 |  |
Depth Buffer
Depth Buffer
When drawing a new pixel, compare new depth to what's stored in depth buffer
| Color | Depth |
|---|
 |  |
Polygons can be drawn in any order
Polygons can intersect
OpenGL Depth Buffering
Space must be allocated for the depth buffer:
glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE|GLUT_DEPTH)
Depth buffering must be enabled:
glEnable(GL_DEPTH_TEST)
Depth buffer must be cleared each frame:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
Depth Fighting
Depth values have limited resolution
i.e. the numbers are not infinitely precise
Rounding errors occur when polygons are filled
Polygon overlap can cause "depth-fighting"
Perspective Projection
Perspective effects are created by a perspective projection transformation
- Linear perspective
- Relative size
- Relative height
- Texture gradient
Perspective + movement also yields motion parallax
Orthographic Projection
Orthographic projection : projects rectilinear box onto display
Objects will not appear to change size with distance
Perspective Projection
Perspective projection : projects frustum (truncated pyramid) onto disp
lay
Near objects appear larger, distant objects appear smaller
Perspective Projection
GL's perspective projection is, conceptually, a pin-hole camera, located at origin, looking down -Z axis
Camera has a field-of-view - angle representing (horizontal)
extent of region viewed
Small angle = narrow field-of-view = telephoto lens
Large angle = wide field-of-view = wide-angle lens
OpenGL Perspective
gluPerspective( fovy, aspect, zNear, zFar )
fovy = field of view, in Y direction, in degrees
aspect = aspect ratio (X:Y) of window
zNear = distance to near clipping plane
zFar = distance to far clipping plane
The "eye-point" of the perspective projection is at (0,0,0)
Example:
gluPerspective(45, 1.333, 0.1, 100)
This document is by Dave Pape, and is released under a Creative Commons BY-2.0 License.
