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# Mar 11 - PowerPoint PPT Presentation

Space Partitions Today’s Short Film Arnold Announcement Proxy Settings for accessing SIGGRAPH papers online. Two paper presentations each on March 18 & 25. 3/18: Portal paper and BSP paper. Read the papers before class. Volunteers wanted for paper presentations on April 8

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## PowerPoint Slideshow about 'Mar 11' - johana

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### Space Partitions

Arnold

• Proxy Settings for accessing SIGGRAPH papers online.

• Two paper presentations each on March 18 & 25.

• 3/18: Portal paper and BSP paper.

• Read the papers before class.

• Volunteers wanted for paper presentations on April 8

• Line/object intersection

• Given a ray or line, which object will it intersect?

• View frustum culling

• Collision detection

• Sequential search is too slow for large models.

• How about storing them in a 3D array?

• Size will be overwhelming

• Think “hierarchy”

• Divide the space in halves in X/Y/Z.

• Always split in the middle.

• You may also consider them as splitting in X, then in Y, then in Z.

• If too many objects are in a partition, divide them again (recursively).

• More flexible than octree:

• Not always splitted in the middle.

• Split in X, then in Y, then in Z, or any order.

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Figure Source: CS638 slides by Stephen Chenney, University of Wisconsin – Madison,

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• From the paper by Fuchs et al, “On visible surface generation by a priori tree structures” SIGGRAPH 80.

• Binary Space Partition trees

• A sequence of cuts that divide a region of space into two

• Cutting planes can be of any orientation

• BSP tress can be used to order polygons from back to front, or visa-versa

• Descend tree with viewpoint

• Things on the same side of a splitting plane as the viewpoint are always in front of things on the far side

• Can draw from back to front

• Gives the correct order for rendering transparent objects with a z-buffer, and by far the best way to do it

• Can draw front to back too.

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Figure Source: CS638 slides by Stephen Chenney, University of Wisconsin – Madison,

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• OBB stands for Oriented Bounding Box.

• OBB is a rectangular bounding box at an arbitrary orientation.

• Asymptotically faster for close proximity situations.

• You may write your own like this:

x -= mouse_ref_x;

y -= mouse_ref_y;

xf = (float) x/width;

yf = (float) y/height;

angle = 90* xf;

M = rotation3D(axis_Y, angle);

angle = 90* yf;

M = rotation3D(axis_X, angle) * M;

• So you don’t have to reinvent the wheel.

• Used in some NVIDIA SDK Demos.

• #include <glh_glut.h>

• glut_simple_mouse_interactor camera, object, *current_interactor;

current_interactor = &camera;