Chap 9' Discrete Techniques

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Chap 9. Discrete Techniques

• 9-1. Buffers and Mappings
• 9-2. Texture Mapping
• 9-3. Environmental Maps
• 9-4. Bump Maps
• 9-5. Writes into Buffers
• 9-6. Bits and Pixel Operations in OpenGL
• 9-7. Compositing Techniques
• 9-8. Use of the Accumulation Buffer
• 9-9. Sampling and Aliasing

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Graphics Pipeline
Application-specific processing
Pixel processing
Polygon processing
Scene processing
Scene graph
Display list
Frame buffer
Depth buffer
Texture memory
(X, Y, Z), M
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Application-specific processing
Pixel processing
Polygon processing
Scene processing
Scene graph
Display list
Frame buffer
Depth buffer
Texture memory
Video memory
CPU
Main memory
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9-5. Raster Operations

• Raster operations (bit-block transfer)
• access to the frame buffer.
• Why do we need them?
• screen clean,
• our own scan conversion algorithm,
• character display, other unthinkable effects.

Basic operation
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• Access to frame buffer is different from access
  to memory.

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• d lt--- f ( d, s )
• There are 16 different functions ( modes ).

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• Assume 0 for background,
• 1 for foreground.
• mode 0 Clear with the background color.
• mode 15Clear with the foreground color.
• mode 37 Write.

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• Mode 6 XOR
• x ( x XOR y ) XOR y
• Implementing a menu
• Screen ? Screen XOR Menu
• Menu ? Screen XOR Menu
• Screen ? Screen XOR Menu
• cursor
• rubberband

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9-6. Bit and Pixel Ops in OpenGL
Application-specific processing
Pixel processing
Polygon processing
Scene processing
Scene graph
Display list
Frame buffer
Z- buffer
OpenGL buffers - color (frame) buffers - depth
(z-) buffer - accumulation buffer (Section 9-8) -
stencil buffer (masking buffer)
Texture memory
A-buffer
S-buffer
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• Frame buffers
• 1 for single buffering
• 2 for double buffering (front/back)
• 4 for stereo imaging
• Operations on the frame buffers
• font display
• read/write buffers
• read/write LUT
• Picking
• Buffer holds the identifiers.

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9-7. Compositing (Blending) Techniques

• Computation capability of FB
• Alpha channel -- (R,G,B,A)

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• I ( R, G, B, A )
• Id ? Is
• Id ? d?Id s?Is
• where d s blending factors

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• 1) image compositing

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• 2) anti-aliasing

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• 3) spatting (foot-noting)

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• 4) depth cueing (fogging)

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9-8. Accumulation Buffer

• A-buffer
• same size as frame buffer
• larger depth
• A-buffer A-buffer ltadditiongt F-buffer
• F-buffer ? A-buffer
• example
• glClear (GL_ACCUM_BUFFER_BIT)
• for ( i0 i lt num_images i)
• glClear (GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT
  S)
• display_image (i)
• glAccum (GL_ACCUM, 1.0 / (float)num_images )
• glAccum (GL_RETURN, 1.0)

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• Usages
• blending
• anti-aliasing
• scene-level, rather than primitive level
• shift (jitter) the camera
• filtering
• depth-of-field effects

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• convolution

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• depth of field effect