CS 445 / 645 Introduction to Computer GraphicsAssignment 3 QuestionsSlide 3Recap: Rendering PipelineInvisible PrimitivesView Frustum ClippingBack-Face CullingSlide 8ManifoldSlide 10Slide 11Slide 12OcclusionPainter’s AlgorithmPainter’s Algorithm: ProblemsAnalytic Visibility AlgorithmsSlide 17Slide 18Binary Space Partition Trees (1979)BSP Trees: ObjectsSlide 21Slide 22Slide 23Slide 24Rendering BSP TreesSlide 26Slide 27Polygons: BSP Tree ConstructionPolygons: BSP Tree TraversalDiscussion: BSP Tree ConsBSP DemoSummary: BSP TreesOctreesWarnock’s Algorithm (1969)Warnock’s AlgorithmSlide 36The Z-Buffer AlgorithmSlide 38Slide 39Slide 40Slide 41Interpolating ZSlide 43Z-Buffer ProsZ-Buffer ConsCS 445 / 645Introduction to Computer GraphicsLecture 20Lecture 20VisibilityVisibilityLecture 20Lecture 20VisibilityVisibilityAssignment 3 QuestionsCan you draw a blank FLTK window?Can you draw a blank FLTK window?Can you put a quadrilateral in the window?Can you put a quadrilateral in the window?Can you put a texture map on the quad?Can you put a texture map on the quad?Can you write a function that changes the colors Can you write a function that changes the colors of all the texels of the loaded texture map to white of all the texels of the loaded texture map to white when you hit the return key?when you hit the return key?Can you draw a blank FLTK window?Can you draw a blank FLTK window?Can you put a quadrilateral in the window?Can you put a quadrilateral in the window?Can you put a texture map on the quad?Can you put a texture map on the quad?Can you write a function that changes the colors Can you write a function that changes the colors of all the texels of the loaded texture map to white of all the texels of the loaded texture map to white when you hit the return key?when you hit the return key?Assignment 3 QuestionsCan you record where in the FLTK window Can you record where in the FLTK window someone clicks the mouse?someone clicks the mouse?Can you draw a point where mouse is clicked?Can you draw a point where mouse is clicked?Can you draw a line between points?Can you draw a line between points?Can you add a button to FLTK window?Can you add a button to FLTK window?Can you use button to change the loaded texture Can you use button to change the loaded texture map to all white?map to all white?Can you record where in the FLTK window Can you record where in the FLTK window someone clicks the mouse?someone clicks the mouse?Can you draw a point where mouse is clicked?Can you draw a point where mouse is clicked?Can you draw a line between points?Can you draw a line between points?Can you add a button to FLTK window?Can you add a button to FLTK window?Can you use button to change the loaded texture Can you use button to change the loaded texture map to all white?map to all white?Recap: Rendering Pipeline•Modeling transformationsModeling transformations•Viewing transformationsViewing transformations•Projection transformationsProjection transformations•ClippingClipping•Scan conversionScan conversionWe now know everything about how to draw a We now know everything about how to draw a polygon on the screen, except polygon on the screen, except visible surface visible surface determinationdetermination •Modeling transformationsModeling transformations•Viewing transformationsViewing transformations•Projection transformationsProjection transformations•ClippingClipping•Scan conversionScan conversionWe now know everything about how to draw a We now know everything about how to draw a polygon on the screen, except polygon on the screen, except visible surface visible surface determinationdeterminationInvisible PrimitivesWhy might a polygon be invisible?Why might a polygon be invisible?•Polygon outside the Polygon outside the field of viewfield of view•Polygon is Polygon is backfacingbackfacing•Polygon is Polygon is occludedoccluded by object(s) nearer the viewpointby object(s) nearer the viewpointFor efficiency reasons, we want to avoid spending work For efficiency reasons, we want to avoid spending work on polygons outside field of view or backfacingon polygons outside field of view or backfacingFor efficiency and correctness reasons, we need to know For efficiency and correctness reasons, we need to know when polygons are occludedwhen polygons are occludedWhy might a polygon be invisible?Why might a polygon be invisible?•Polygon outside the Polygon outside the field of viewfield of view•Polygon is Polygon is backfacingbackfacing•Polygon is Polygon is occludedoccluded by object(s) nearer the viewpointby object(s) nearer the viewpointFor efficiency reasons, we want to avoid spending work For efficiency reasons, we want to avoid spending work on polygons outside field of view or backfacingon polygons outside field of view or backfacingFor efficiency and correctness reasons, we need to know For efficiency and correctness reasons, we need to know when polygons are occludedwhen polygons are occludedView Frustum ClippingRemove polygons entirely outside frustumRemove polygons entirely outside frustum•Note that this includes polygons “behind” eye (actually Note that this includes polygons “behind” eye (actually behind near plane)behind near plane)Pass through polygons Pass through polygons entirely inside frustumentirely inside frustumModify remaining polygonsModify remaining polygonsto include only portions to include only portions intersecting view frustumintersecting view frustumRemove polygons entirely outside frustumRemove polygons entirely outside frustum•Note that this includes polygons “behind” eye (actually Note that this includes polygons “behind” eye (actually behind near plane)behind near plane)Pass through polygons Pass through polygons entirely inside frustumentirely inside frustumModify remaining polygonsModify remaining polygonsto include only portions to include only portions intersecting view frustumintersecting view frustumBack-Face CullingMost objects in scene are typically “solid”Most objects in scene are typically “solid”More rigorously: More rigorously: compact, orientable manifoldscompact, orientable manifolds•Must not cut through itselfMust not cut through itself•Must have two distinct sidesMust have two distinct sides– A sphere is orientable since it has A sphere is orientable since it has two sides, 'inside' and 'outside'.two sides, 'inside' and 'outside'.– A Mobius strip or a Klein bottle is not A
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