CS 112 The Rendering Pipeline. Slide 1

Transcription

1 CS 112 The Rendering Pipeline Slide 1

2 Rendering Pipeline n Input 3D Object/Scene Representation n Output An image of the input object/scene n Stages (for POLYGON pipeline) n Model view Transformation n Projection Transformation n Clipping and Vertex Interpolation of Attributes n Rasterization and Pixel Interpolation of Attributes Slide 2

3 Rendering Pipeline n Input 3D Object/Scene Representation n Output An image of the input object/scene n Stages n Model-view Transformation n Projection Transformation n Clipping and Vertex Interpolation of Attributes n Rasterization and Pixel Interpolation of Attributes Slide 3

4 Model-view Transformation n Model Transformation n View Transformation n World Coordinate System n Object Coordinate System Slide 4

5 World and Object Coordinates Y W Y O X O Z W X W Z O Y O Y O X O MODEL TRANSFORMATION X O Z O Z O Slide 5

6 Model Transformation n Transforming from the object to world coordinates n Placing the object in the desired position, scale and orientation n Can be done by any kind of transformations n Graphics hardware/library support only linear transformations like translate, rotate, scale, and shear Slide 6

7 View Transformation Y W X W Z W Slide 7

8 View Transformation n Position and orientation of eye (9 parameters) n View point - POINT : (x, y, z) [3] n Normal to the image plane VECTOR: (vx, vy,vz) [3] n View Up VECTOR: (ux, uy,uz) [3] n Default: (0,0,0), (0,0,-1), (0,1,0) n Transformation to align n n n n Eye with the origin Normal to the image plane with negative Z axis View Up vector with positive Y axis Can be achieved by rotation and translation Slide 8

9 Rendering Pipeline n Input 3D Object/Scene Representation n Output An image of the input object/scene n Stages n Model view Transformation n Projection Transformation n Clipping and Vertex Interpolation of Attributes n Rasterization and Pixel Interpolation of Attributes Slide 9

10 Projection Transformation n Define the view frustum (6 parameters) n Assume origin is the view point n Near and far planes (planes parallel to XY plane in the negative Z axis) [2] n Left, right, top, bottom rectangle defined on the near plane [4] Y -Z X near far Slide 10

11 Projection Transformation n Transforming the view frustum (along with the objects inside it) into a n cuboid with unit square faces on the near and far planes n the negative Z axis passes through the center of these two faces. n Projecting the objects on the near plane n Consists of a shear and a perspective projection operations. Slide 11

12 Projection Transformation Y X Z Slide 12

13 Important n Every vertex undergoes the modelview and projection transformation n Geometric transformation n Topology does not change n Even when transforming triangles n Sufficient to transform the vertices Slide 13

14 Rendering Pipeline n Input 3D Object/Scene Representation n Output An image of the input object/scene n Stages n Model view Transformation n Projection Transformation n Clipping and Vertex Interpolation of Attributes n Rasterization and Pixel Interpolation of Attributes Slide 14

15 Clipping n Removing the part of the polygon outside the view frustum n If the polygon spans inside and outside the view frustum n introduce new vertices on the boundary Slide 15

16 Interpolation of Attributes n For the new vertices introduced n compute all the attributes n Using interpolation of the attributes of all the original vertices Slide 16

17 Interpolation of Attributes n For the new vertices introduced n compute all the attributes n Using interpolation of the attributes of all the original vertices Slide 17

18 Window Coordinate Transformation n Scale XY coordinates of unit cuboid to reflect size of window (relative pixel coordinates) n Translate these coordinates to the position of the window on the monitor screen to represent the absolute pixel coordinates. n Z value is used for resolving occlusion Slide 18

19 Rendering Pipeline n Input 3D Object/Scene Representation n Output An image of the input object/scene n Stages n Model view Transformation n Projection Transformation n Clipping and Vertex Interpolation of Attributes n Rasterization and Pixel Interpolation of Attributes Slide 19

20 Rasterization n Process of generating pixels in the scan (horizontal) line order (top to bottom, left to right). n Which pixels are in the polygon Scan Line left right left right Slide 20

21 Interpolation of Attributes n Interpolate the colors and other attributes at pixels from the attributes of the left and right extent of the scan line on the polygon edge. n Also in scan line order Scan Line left right left right Slide 21