The Rendering Pipeline

Transcription

1 The Rendering Pipeline

2 Framebuffers Framebuffer is the interface between the device and the computer s notion of an image A memory array in which the computer stores an image On most computers, separate memory bank from main memory Many different variations, motivated by cost of memory

3 Framebuffers: True-Color A true-color (aka 24-bit or 32-bit) framebuffer stores one byte each for red, green, and blue Each pixel can thus be one of 2 24 colors Pay attention to Endian-ness How can 24-bit and 32-bit mean the same thing here?

4 Framebuffers: Indexed-Color An indexed-color (8-bit or PseudoColor) framebuffer stores one byte per pixel (also: GIF image format) This byte indexes into a color map: How many colors can a pixel be? Common on low-end displays (cell phones, PDAs, GameBoys)

5 Framebuffers: Indexed Color Illustration of how an indexed palette works A 2-bit indexed-color image. The color of each pixel is represented by a number; each number corresponds to a color in the palette. Image credits: Wikipedia

6 Framebuffers: Hi-Color Hi-Color is (was?) a popular PC SVGA standard Packs pixels into 16 bits: 5 Red, 6 Green, 5 Blue (why would green get more?) Sometimes just 5,5,5 Each pixel can be one of 2 16 colors Hi-color images can exhibit worse quantization artifacts than a well-mapped 8-bit image

7 Color Quantization A process that reduces the number of distinct colors used in an image Intention that the new image should be as visually similar as possible to the original image Image credits: Wikipedia

8 The Rendering Pipeline: A Tour Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

9 The Display You Know Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

10 The Framebuffer You Know Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

11 The Rendering Pipeline Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

12 2-D Rendering: Rasterization Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

13 The Rendering Pipeline: 3-D Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

14 The Rendering Pipeline: 3-D Scene graph Object geometry Result: Modeling s Lighting Calculations Viewing Clipping Projection All vertices of scene in shared 3-D world coordinate system Vertices shaded according to lighting model Scene vertices in 3-D view or camera coordinate system Exactly those vertices & portions of polygons in view frustum 2-D screen coordinates of clipped vertices

15 The Rendering Pipeline: 3-D Scene graph Object geometry Result: Modeling s Lighting Calculations Viewing Clipping Projection All vertices of scene in shared 3-D world coordinate system Vertices shaded according to lighting model Scene vertices in 3-D view or camera coordinate system Exactly those vertices & portions of polygons in view frustum 2-D screen coordinates of clipped vertices

16 Rendering: ations So far, discussion has been in screen space But model is stored in model space (a.k.a. object space or world space) Three sets of geometric transformations: Modeling transforms Viewing transforms Projection transforms

17 The Rendering Pipeline: 3-D Scene graph Object geometry Result: Modeling s Lighting Calculations Viewing Clipping Projection All vertices of scene in shared 3-D world coordinate system Vertices shaded according to lighting model Scene vertices in 3-D view or camera coordinate system Exactly those vertices & portions of polygons in view frustum 2-D screen coordinates of clipped vertices

18 Rendering: Lighting Illuminating a scene: coloring pixels according to some approximation of lighting Global illumination: solves for lighting of the whole scene at once Local illumination: local approximation, typically lighting each polygon separately Interactive graphics (e.g., hardware) does only local illumination at run time

19 The Rendering Pipeline: 3-D Scene graph Object geometry Result: Modeling s Lighting Calculations Viewing Clipping Projection All vertices of scene in shared 3-D world coordinate system Vertices shaded according to lighting model Scene vertices in 3-D view or camera coordinate system Exactly those vertices & portions of polygons in view frustum 2-D screen coordinates of clipped vertices

20 Rendering: Clipping Clipping a 3-D primitive returns its intersection with the view frustum:

21 Rendering: Clipping Clipping is tricky! Clip In: 3 vertices Out: 6 vertices Clip In: 1 polygon Out: 2 polygons

22 The Rendering Pipeline: 3-D Illuminate Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display

23 Trivia The first blockbuster to use CGs was Star Wars in The 40-second Death Star simulation sequence took the animation company Cuba 12 weeks to produce!