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Topic: Backface Culling

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	Gamasutra - Features - "Compact Backface Culling" [08.06.99] (Site not responding. Last check: 2007-10-25)
		This highly accurate technique, which performs accurate backface culling in object space, is particularly applicable to front-end culling, and requires only half as much storage as the standard facet-normal technique.
		Culling during stages 2 and 3 is typically performed in screen space by checking the clockwise/counterclockwise order of a polygon's vertices.
		The real expense of front-end culling is that we either have to calculate the facet normal on the fly or use a precalculated facet normal, which increases the size of our model database.
	www.gamasutra.com /features/19990806/compact_backface_culling_01.htm (601 words)

	Does Blitz3D has a backface culling system? - BlitzCoder (Site not responding. Last check: 2007-10-25)
		with backface culling if you have a sphere, only the visible polys will be rendered so the camera is actually drawing a hemisphere not a sphere at all, as anything that the camera can't see is taken out.
		Backface culling is dynamic as the camera moves aroudn a object onlt the visible polys are drawn.
		Backface culling is the omission of polys that face away from the camera, this is determined by the direction (clockwise/anti-clockwise) of the 2d screen coords of the vertices.
	www.blitzcoder.com /cgi-bin/ubb-cgi/postdisplay.cgi?forum=Forum1&topic=003335 (1430 words)

	nV News - NVIDIA GeForce3 Preview - Occlusion Culling
		As discussed in the section on Lightspeed Memory Architecture, occlusion culling is a feature of the GeForce3, which is used to reduce the amount of memory and processing required by a 3D graphics application.
		Backface Culling - removes objects that are facing away from the camera viewport.
		The idea behind occlusion culling using the Z-buffer is to test whether on object is located closer to the camera (player viewport) than the current depth buffer value.
	www.nvnews.net /previews/geforce3/occlusion_culling.shtml (955 words)

	[No title]
		Backface Culling Probably the most-used algorithm for culling polygons is to consider the polygon to only have one visible side, and to cull the polygon if it is facing away from the camera.
		Culling a polygon because it is facing "away" from the camera (ie has it's "back" to the camera) is, as you might suspect, called backface culling.
		If the poly wasn't culled, go through and transform the X and Y vertex values from world-space to clip-space, combine them with the saved Z transforms (just a waste of time to transform them twice), and continue with clipping etc (the poly is now transformed into clip-space).
	www.phys.uu.nl /~0307467/docs/pcull3d.txt (1651 words)

	3D:Backface Culling - GPWiki
		Backface Culling can be considered part of the Hidden Surface Removal process of a Rendering Pipeline.
		Backface Culling is the process by which Polygons (usually triangles) that are not facing the Camera are removed from the Rendering Pipeline.
		The first step in backface culling, believe it or not, is the loading of the polygon data.
	gpwiki.org /index.php/3D:Backface_Culling (1472 words)

	kirupa.com - Backface Culling
		The process of determining this visibility is commonly refereed to as backface culling.
		There are a couple ways of determining backface culling, whether or not a particular triangle or face in 3D is to be drawn or not.
		Backface culling is not the only way to make a 3D shape solid.
	www.kirupa.com /developer/actionscript/backface_culling.htm (1576 words)

	C Board - Backface Culling in Lesson10 NeheGL Tutorials
		Backface culling works because if a polygon is facing in a positive z direction, it is facing away from the camera/viewer.
		In order for backface culling to work correctly you must know what type of coordinate system you are using.
		This simple, and not always accurate, backface cull will only work when all polygons are designed so that when they are viewed from their visible sides, the vertexes proceed around the polygon in a counterclockwise direction.
	cboard.cprogramming.com /printthread.php?t=1057 (278 words)

	[No title]
		However, there are some programs that rely on backface culling tricks to render properly, such as the 2-color helix ribbons that Molscript generates - in fact, this is the reason why I put this somewhat troublesome option in here at all.
		If backface culling is to be done, the first node present in the VRML file must be a Viewpoint node.
		The reason for this is that the calculations required for backface culling depend upon the viewpoint position, so this must be known in advance, before things like IndexedFaceSet are converted into POV objects.
	www.chemicalgraphics.com /paul/vrml2pov/README (826 words)

	VERC · Half-Life's In-Game Visibility Determination
		All that backface culling does is simply remove every triangle that is facing away from the viewer, as they probably wouldn't (and shouldn't) be visible anyway.
		Culled, if the node was not in the PVS for this frame.
		In the hardware renderer, the surfaces found in the BSP leaves are backface culled by the 3D accellerator.
	collective.valve-erc.com /index.php?doc=1038660504-05211700 (2641 words)

	Backface Culling?
		Backface culling keeps triangles that your looking at the back of from being drawn.
		If you go inside that sphere, and backface culling is enabled, which it normally is, then you will see the outside world.
		Incidentally, if you disable backface culling, the textures on the inside will be the same as the outside, but backwards, and all the lighting will be inverted, so what you think should be lit won't be, and vice versa.
	www.blitzbasic.com /Community/posts.php?topic=37351 (201 words)

	SLIDE Back Face Culling Page
		Back face culling is when you do not render a polygon because its normal is pointing away from the viewer's eye point.
		A naive way of preforming this check would be to construct a vector from the eye point to a point on the face and compute the dot product of this line of sight vector and the normal vector.
		Then the check for back face culling is just to see if the Z component of the transformed normal is negative.
	www.cs.berkeley.edu /~ug/slide/pipeline/assignments/backfacecull.shtml (945 words)

	Hybrid Graphics :: View topic - the techonoly about how to promote opengl es performance (Site not responding. Last check: 2007-10-25)
		The pipeline contains lots of different culling techniques (such as backface culling, view frustum culling, scissoring test, scan conversion output test etc.) that are all performed before the lighting pipeline, so shading has been deferred to happen as late as possible.
		In order to do back-face culling prior to transformation (this is called "object-space back-face culling") you need to transform the camera's position into object space, and this obviously requires computing the inverse of the object's matrix.
		The culling is related to the arithmetic precision so that we can not perform back-face culling in the object-space.
	forum.hybrid.fi /viewtopic.php?p=82 (1221 words)

	OpenGL:Tutorials:Tutorial Framework:Adding Depth and Color - GPWiki
		Another technique that aids the illusion is backface culling.
		Backface culling also reduces the on screen polycount by around a half, so it is a valuable optimisation.
		Try commenting out the Z-Buffer and backface culling commands to see how the illusion is destroyed when the polygons are not displayed correctly.
	gpwiki.org /index.php/OpenGL_Tutorial_Framework:Adding_Depth_and_Color (592 words)

	AndyC.org : Articles
		Mechanisms for doing so are referred to as "culling mechanisms" because of their nature to select only certain objects from a larger set (flock) of objects.
		Some well-known culling mechanisms include backface culling, which prevents the rasterization of any fragments on a polygon known to be "facing away" from the viewing position, and frustum culling, which prevents the consideration of polygons belonging to objects that are entirely outside the viewing frustum (field of view).
		Due to the high cost of the hierarchy generation, all occluders must be selected and rasterized before visibility testing can be performed; this can be problematic if near and far objects in the scene provide occlusion, and thus the selection of occluders is a matter that benefits from tweaking for specific scenes or scene types.
	www.andyc.org /articles/viewarticle.php?id=7 (1730 words)

	VTK: vtkProperty Class Reference
		The primary properties that can be set are colors (overall, ambient, diffuse, specular, and edge color); specular power; opacity of the object; the representation of the object (points, wireframe, or surface); and the shading method to be used (flat, Gouraud, and Phong).
		Turn on/off fast culling of polygons based on orientation of normal with respect to camera.
		If backface culling is on, polygons facing away from camera are not drawn.
	noodle.med.yale.edu /vtk/classvtkProperty.html (1073 words)

	Backface Culling (Site not responding. Last check: 2007-10-25)
		A simple way to perform hidden surface is to remove all ``backfacing'' polygons.
		The observation is that if polygon normal is facing away from the viewer then it is ``backfacing.''
		For solid objects, this means the polygon will not be seen by the viewer.
	medialab.di.unipi.it /web/IUM/Waterloo/node66.html (149 words)

	Object Space Rejection
		Typically this job is left to backface culling which can remove approximately half the workload from all your 3D routines by cutting your object in half and removing all those polygons which are invisible (see my backface culling article for more information).
		However, this method also assumes that you've transformed all your points into world space, seeing as though you must cull against the camera's position, which is specified in world space.
		Not only could you skip transforming all your points into world space just to end up rejecting half of them, but you also would be able to shade your object in object space, thereby removing the need to transform the many polygon and vertex normals.
	www.whisqu.se /per/docs/article40.htm (905 words)

	[No title]
		Since frustum culling is essentially a 3D world-space procedure, it can be processed long before we even deal with individual polygons in our pipeline.
		Once we cull a top level node, we don’t have to cull lower level nodes since they cannot be visible anyway.
		Without a hierarchal method, frustum culling still has a good advantage over not doing it at all but it also means that it scales linearly with the number of objects in our world.
	www.flipcode.com /articles/article_frustumculling-pf.shtml (4276 words)

	Backface Culling and Dot-Products... - GameDev.Net Discussion Forums (Site not responding. Last check: 2007-10-25)
		Basically, I have an array of normal vectors (one for each face in my mesh) - before I render the mesh, I want to cull the backfaces away from it, but something doesn't seem to be working right...
		Because backface culling requires post-projection vertices, doing it in software is just wrong.
		I'm considering to do software-based fustrum culling for stars myself, but it's because i don't really need to really check each star...(subdivision) and because i anyway need to align billboards for older cards that doesn't have point sprites.
	www.gamedev.net /community/forums/viewreply.asp?ID=1616174 (1629 words)

	iDevGames - Community Forum - GL backface culling
		Because the back face culling process is pretty standard and is probably always hardware accelerated, there is no way you could out-perform it using a custom algorithm.
		I can't say that I know the complete details of OpenGL's algorithm, but I believe it creates a line between the first two verts in a triangle and checks which side the third vert is on (probably in the order submitted but I have no real idea).
		If you culled yourself, I think you'd have to resubmit the array or rebuild the list every time a triangle was hidden or revealed.
	www.idevgames.com /forum/printthread.php?t=12 (477 words)

	ZeusCMD - Design and Development Tutorials : OpenGL ES Programming Tutorials - Backface Culling
		When creating a 3D object such as the box in the previous tutorial, we do not need the backs of the primitives(polygons) to be displayed.
		A technique known as backface culling is available to us to prevent the backfaces of the polygons from being rendered.
		For every unseen polygon that is culled, another one can be rendered to make a different object more detailed.
	www.zeuscmd.com /tutorials/opengles/14-BackfaceCulling.php (448 words)

	Backface culling (Site not responding. Last check: 2007-10-25)
		If we state V is the vector from the eye, and N is the normal, we need only see if they are pointing in the same direction, i.e.
		We can cull out these backfacing polygons early in the pipeline, which means we avoid lighting them, texturing them, transforming them, clipping them, etc. But backface is much easier after the viewing transformation, because that means that the viewing direction V is along the z-axis.
		So backface culling is almost always done as early as possible in the pipeline.
	www.cs.nps.navy.mil /people/faculty/capps/iap/class5/backface (448 words)

	Using Quesa - Geometry Objects (Site not responding. Last check: 2007-10-25)
		For objects which are not transparent, backface culling may be turned on to remove those polygons which will not be visible in the final scene.
		To perform backface culling, renderers require a normal for each polygon.
		To reduce the overhead of calculating these normals, you should supply triangle normals for all polygonal geometry if you intend to use backface culling.
	www.quesa.org /developer/book/08_geometry (128 words)

	Doom3 world :: View topic - forcing a texture not to repeat
		frontface culling may occure where the whole faces or even the whole object the face is part of are behind another face (wall..
		It is used if the keyword "cull" appears in the content instructions without a value or if the keyword cull does not appear at all in the shader.
		Cull back removes the back or "inside" of a polygon from being drawn in the world.
	www.doom3world.org /phpbb2/viewtopic.php?t=10085 (1111 words)

	SoShapeHints class Reference
		For example, if an object is solid and has ordered vertices, Open Inventor turns on backface culling and turns off two-sided lighting.
		If the object is not solid but has ordered vertices, it turns off backface culling and turns on two-sided lighting.
		In all other cases, both backface culling and two-sided lighting are off.
	www.tgs.com /support/java_api_doc/api_cpp/html/classSoShapeHints.html (845 words)

	kirupa.com - Solid Pyramids
		One uses the visibility function for backface culling and the other uses separate movieclips for faces and uses swapDepths for each of those clips to properly arrange them.
		This will be used in the first pyramid for backface culling taking three of the points making up a face in the pyramid and determining visibility of that face based on slope and position of each point in relation to each other.
		The first will be the one with backface culling using the isVisibleBetween function defined earlier.
	www.kirupa.com /developer/actionscript/solid_pyramids.htm (1324 words)

	Backface Culling Using Normal Masks (Site not responding. Last check: 2007-10-25)
		This is a novel method for fast and efficient backface culling: we reduce the backface test to one logical operation per polygon while requiring only two bytes extra storage per polygon.
		For each frame (and for each viewing volume), we calculate the backface mask by ORing the normals masks of all normal clusters that are backfacing.
		The backface test finally reduces to a single logical AND operation between the polygon's normal mask and the backface mask.
	www.cs.unc.edu /~zhangh/backface.html (186 words)

	Graphics (Site not responding. Last check: 2007-10-25)
		Turning backface culling on means that only front-facing triangles are drawn, and thus rendering is about 1.5 times faster.
		In general, however, it's best to use backface culling for the performance enhancement, unless clipping is active, when the decision to use culling will be dependent on the current model.
		Normally, the back face of all polygons is rendered with the currently defined backface material as controlled by the material editor (§ 6.11.4), usually an amorphous gray color.
	quorum.tamu.edu /Manual/Manual/node35.html (5291 words)

	Gamasutra - Features - "Compact Backface Culling" [08.06.99] (Site not responding. Last check: 2007-10-25)
		This appendix contains a C++ implementation with all four methods: non-compact culling, compact scalar culling, compact SIMD culling, and compact SIMD culling with prefetch instructions.
		The compact backface culling routine is much the same as the previous one, except for the fixed-point calculations and the use of the precalculated dot product.
		The compact SIMD backface culling routine is much the same as the compact culling routine, except for the use of the vector classes for parallelism.
	www.gamasutra.com /features/19990806/compact_backface_culling_05.htm (413 words)

	DX Backface culling Slower than...... - GameDev.Net Discussion Forums
		I used to work on a PC with an AGP bus that was so slow that a culling in software would have been more efficient than a hardware one.
		If you are always building the index buffer, then the difference is going to be that when you cull on the CPU are you build an index buffer that is likely half the size and thus you are sending half the index data across the bus.
		If you are going to let the GPU do the culling, then you should use a static index buffer.
	www.gamedev.net /community/forums/topic.asp?topic_id=307559 (583 words)

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