CA417 graphics exam notes January 2007 ... some flaky shit in there. covers.... Java3D a few general graphics definitions a few transform matrices almost nothing else Most of the Java3D stuff is too detailed for single flashcards, which means you end up repeating the same card 20 times because you left out one of 30 steps. Sorry about that. I was in a rush and not sure how to organise the information in more bite-sized chunks and still get everything. Suggestions on a postcard... Oisín macfheo2@mail.dcu.ie what does the View do? maps the viewpoint onto a 2D image in a Canvas3D what aspect of the ViewPlatform determines how much of the scene appears in the Canvas3D? field of view how can the ViewPlatform be moved about the world to change the rendered image? place the ViewPlatform in a TransformGroup and move that what is the default projection used by View? perspective projection setNominalViewingTransform() moves the ViewPlatform so that... the range [-1, 1] is visible in the X and Y axes at z = 0. what is the default FOV? what method (in what class) changes the FOV? View.setFieldOfView(double fov); given a scene BoundingSphere radius "radius" (...), what formula gives an approximately useful viewing distance on the z axis? viewDistance = 1.4 * radius / tan(FOV/2); what homogenous coordinate represents the same point as (1, 4, 7) where W = 21? (3, 12, 21) what is and is not preserved in an affine transformation? parallel lines, but not lengths or angles 3D translation matrix p' = t*p [ x' ] [ 1 0 0 Tx ][ x ] | y' | | 0 1 0 Ty || y | | z' |=| 0 0 1 Tz || z | [ 1 ] [ 0 0 0 1 ][ 1 ] 3D scaling matrix p' = s*p [ x' ] [ Sx 0 0 0 ][ x ] | y' | | 0 Sy 0 0 || y | | z' |=| 0 0 Sz 0 || z | [ 1 ] [ 0 0 0 1 ][ 1 ] 3D z-axis rotation matrix [ x' ] [ cosA -sinA 0 0 ][ x ] | y' | | sinA cosA 0 0 || y | | z' |=| 0 0 1 0 || z | [ 1 ] [ 0 0 0 1 ][ 1 ] 3D x-axis rotation matrix [ x' ] [ 1 0 0 0 ][ x ] | y' | | 0 cosA -sinA 0 || y | | z' |=| 0 sinA cosA 0 || z | [ 1 ] [ 0 0 0 1 ][ 1 ] 3D y-axis rotation matrix [ x' ] [ cosA 0 sinA 0 ][ x ] | y' | | 0 1 0 0 || y | | z' |= | -sinA 0 cosA 0 || z | [ 1 ] [ 0 0 0 1 ][ 1 ] general form of a composition of 3D transformations [ R11 R12 R13 Tx] | R21 R22 R23 Ty| | R31 R32 R33 Tz| [ 0 0 0 1] what defines the projection onto the projection plane (viewport?) the projection is defined by projection rays (projectors) that come from a centre of projection (COP), pass through each point of the object and intersect with the projection plane what are parallel and perspective projection? projection rays (projectors) come from a centre of projection (COP), pass through each point of the objects in 3D space, and intersect with a projection plane. if the COP is at infinity, we have parallel projection if the COP is at a point, that is perspective projection define perspective foreshortening the apparent size of an object is inversely proportional to its distance to the centre of projection what happens to parallel lines (that aren't parallel to the X axis..?) in perspective projection? they converage on a vanishing point if parallel lines are parallel to one of the principal axes (except X?) in perspective projection, where do they converge? axis vanishing point name the different types of parallel projection orthographic, oblique what is orthographic parallel projection? when the direction of projection and projection plane normal are the same. in orthographic projection, if the projection plane normal is coincident with a principal axis, name 3 common usage examples top (plan) front / side elevations ie... blueprints? in orthographic projection, if the projection plane normal is not... coincident with a principal axis, what is this called, and what is this type of image called? axonometric isometric...: all principal axes equally foreshortened? in oblique projection, define the two common (?) types cabinet angle between DOP and projection plane normal is arctan(2) = 63.4' lines perpendicular to projection plane project to half their length. cavalier angle between DOP and projection plane normal is 45' by what other name is the projection plane known? view plane what is the view plane defined by? view reference point (VRP) and view plane normal (VPN) what does VRC stand for? viewing reference coordinate (system) what is the 3D VRC system formed by? VPN and view-up vector in the 3D VRC system, what do the u, v and n-axes correspond to? u: completes the right-handed coordinate system v: VUP n: VPN in the 3D VRC, how is the viewing window defined? centre of window (CW) and minimum and maximum u and v values what strange acronym refers to the centre of projection? PRP for parallel projection, what defines the view? PRP and direction of projection (DOP) what is the DOP? a vector from the PRP (centre of projection) to the CW what shape is defined by the projectors from the PRP through the minimum and maximum window coordinates (in u and v) in perspective projection? a semi-infinite pyramid view volume what shape is defined by the projectors from the PRP through the minimum and maximum window coordinates (in u and v) in parallel projection? a semi-infinite parallelepiped view volume what does NPC stand for in this context, and what is mapped to it and where? normalised projection coordinates... the view volume, with PRP at the origin and the back clipping plane at 1 what rotation aligns the VPN with the z-axis? Rz = VPN / |VPN| the u-axis is perpendicular to what xyz axis and vector? z-axis and VUP (y-axis) what rotation aligns the u-axis to the x-axis? Rx = (VUP * Rz) / || VUP * Rz || what rotation aligns the v-axis to the y-axis? Ry = Rz * Rx define a 3D shear matrix SHpar = SH(shXpar, shYpar) = [ 1 0 shXpar 0 ] | 0 1 shYpar 0 | | 0 0 1 0 | [ 0 0 0 1 ] what's so good about the "canonical" parallel view volume? easier to clip against and map to 2D device coordinates what clipping algorithm is in ze notes? Cohen-Sutherland name the subclasses (from the notes, anyway) of a Group node? BranchGroup OrderGroup Switch TransformGroup SharedGroup what two main component nodes make up a Shape3D object? Geometry and Appearance what Java3D scene graph object defines the place from which the viewer is looking at the world? ViewPlatform what are the subclasses of Node? Group and Leaf what is the base class for scene graph objects, and what are the two important subclasses? SceneGraphComponent, Node, NodeComponent what does a scene graph represent? the world, the objects in the world, the light sources and the viewpoint what is rasterisation? converting a graphical primitive (points, line, curve etc) into a set of pixels name the 2 categories of viewing device, and give an example of each calligraphic / vector .. e.g. plotter/laser light projection systems raster .. e.g. monitor/printer what does the ViewPlatform represent? the viewer to compose transforms to represent applying A then B then C, what order are the matrix multiplications done in? reverse, genius. T = C * B * A what is needed to effect a rotation? what rule determines the direction rotation? axis to rotate around, angle right hand rule what Transform3D method specifically sets a rotation, and what class is expected? void setRotation(AxisAngle4f angle); show the Transform3D methods used to scale the shape, first uniformly and possibly wasteful, then more specific uniform, then nonuniform void set(double scale); void setScale(double scale); void setScale(Vector3f scaling); create a method that translates a passed in TransformGroup by a passed in vector void move(TransformGroup tg, Vector3f vector) { Transform3D translation; tg.getTransform(translation); translation.setTranslation(vector); tg.setTransform(translation); } apply a transform to a TransformGroup "tg" that translates it 1 unit in the direction of the X axis Vector3f translateVector = new Vector3f(1f, 0f, 0f); Transform3D transform = new Transform3D(); transform.set(translateVector); tg.setTransform(transform); what does setTransform do with the Transform3D? what is worth noting about how it does it? copies the Transform3D to the TransformGroup (matrix?) subsequent changes don't change the TransformGroup unless setTransform() is called again. how do we apply a transform to a TransformGroup? (method call) TransformGroup.... void setTransform(Transform3D transform); what does an Interpolator do? based on what, and what do the the parameters signify? changes a transform or attribute over time based on an Alpha value. Alpha constructor takes 2 values, loop count: -1 means loop forever loop duration in ms what does a Billboard do? controls a TransformGroup to keep its children oriented towards the ViewPlatform what does a DistanceLOD control? what inputs determine which actions? controls a Switch node to provide different levels of detail. distance from ViewPlatform controls which child of the Switch to render name 3 predefined Behavior subclasses DistanceLOD Interpolator Billboard what 2 methods are defined by the Behavior class? void setEnable(boolean state); void setSchedulingBounds(Bounds bounds); how do we make a background change as the viewer moves around the universe? code it with a texture.... TextureLoader bgTexture = new TextureLoader("image.png", null); Background bg = new Background(); bg.setApplicationBounds(infiniteBounds); BranchGroup bgBG = new BranchGroup(); Appearance bgApp = new Appearance(); bgApp.setTexture(bgTexture.getTexture()); Sphere sphereObj = new Sphere(1.0f, Sphere.GENERATE_NORMALS | Sphere.GENERATE_NORMALS_INWARDS | Sphere.GENERATE_TEXTURE_COORDS, 45, bgApp); bgBG.addChild(sphereObj); bg.setGeometry(bgBG); name the two types of Fog supported by Java3D and their parameters? LinearFog (colour, start distance, end distance) ExponentialFog (colour, exponential decay factor) create a red background with infinite bounds (infiniteBounds) Color3f red = new Color3f(1f, 0f, 0f); Background bg = new Background(red); bg.setApplicationBounds(infiniteBounds); create a background with an image (texture) (with infiniteBounds...) java.net.URL image = "images/bg1.png"; TextureLoader bgTexture = new TextureLoader(image, null); Background bg = new Background( bgTexture.getImage()); bg.setApplicationBounds(infiniteBounds); what's the standard (long, that is) SpotLight constructor? SpotLight(colour, position, (float)Math.toRadians(spreadAngle), (float)spotConcentration); create a point light using the variable 'white' for colour, 'position' for position, 'attenuation' for ... attenuation and 'bounds' for bounds. PointLight light = new PointLight( white, position, attenuation); light.setInfluenceBounds(bounds); what does the AmbientLight constructor look like? AmbientLight(colour) what does the concentration of a Spotlight determine? what's the range? how quickly the light intensity falls off as it moves away from the spotlight's direction vector. range is 0-128 where 0 implies no effect and 128 means the light shines in a narrow beam along the direction vector (ie. a laser?) what controls a SpotLight object's spot? spread angle (maximum width) concentration what is the Java3D light attenuation model? intensityD = intensitySource/(const + lin*d + quad*d^2) create a white directional light that can be modified when live BoundingSphere infiniteBounds = new BoundingSphere( new Point3f(), Double.MAX_VALUE); Vector3f lightDir = new Vector3f(0.6f, -0.6f, -0.4f); Color3f white = new Color3f(1f, 1f, 1f); DirectionalLight sun = new DirectionalLight(white, lightDir); sun.setInfluenceBounds(infiniteBounds); sun.setCapability(Light.ALLOW_STATE_WRITE); sun.setCapability(Light.ALLOW_DIRECTION_WRITE); name some capability bits corresponding to Light and DirectionalLight ALLOW_STATE_READ/WRITE ALLOW_COLOR_READ/WRITE ALLOW_DIRECTION_READ/WRITE what are the 4 most useful methods of the Light subclasses? get/setEnable(...) get/setColor(...) describe the different types of lighting directional lights from a distance source (parallel rays) point lights at a specific point in space (lightbulb) spot lights located at a specific point and pointing in a certain direction ambient lights diffusely light an area write a createSceneGraph method to load a texture and apply it to a sphere. public BranchGroup createSceneGraph() { BranchGroup root = new BranchGroup(); TextureLoader loader = new TextureLoader("textureImage.png", null); Texture tex = loader.getTexture(); Appearance app = new Appearance(); TextureAttributes ta = new TextureAttributes(); app.setTextureAttributes(ta); app.setTexture(tex); Sphere ball = new Sphere(0.8f, Primitive.GENERATE_TEXTURE_COORDS, app); ball.setAppearance(app); // ? root.addChild(ball); return root; } define an infinite spherical bounding region centred at the origin BoundingSphere infiniteBounds = new BoundingSphere( new Point3D(), Double.MAX_VALUE); // ?! name the basic bounding regions in Java3D BoundingBox BoundingSphere BoundingPolytope how do we limit the effect of environment nodes on the virtual universe? bounding regions name the four texture modes in the notes. what method (belonging to which class) allows you to set the mode? REPLACE replace object's underlying colour MODULATE mixes texture colour with surface colour. enables lighting effects with texture mapping DECAL uses texture's transparency (alpha) values to determine whether to use texture image or underlying surface BLEND texture image defines how much of texture blend colour is mixed with surface colour TextureAppearance.setTextureMode(int mode); Steps to create image on view port 1. Orient universe a: viewpoint at origin b: viewer looking down an axis 2. Project universe on viewport 3. Clip projection to viewport 4. Remove hidden surfaces 5. Calculate colour/intensity for a point x, y, z on an object, what is the mapping to texture coordinates given by the TexCoordGeneration attribute component in OBJECT_LINEAR mode? s = x*planeS.x + y*planeS.y + z*planeS.z + planeS.w; t = x*planeT.x + y*planeT.y + z*planeT.z + planeT.w; name two ways in which texture coordinates can be specified for an object 1. when object is generated, with the setTextureCoordinates() method if the object is a GeometryArray primitive. 2. automatically with the TexCoordGeneration attribute component. what maps from object geometry to a texture image? texture coordinates what modes are available that effect how a texture is scaled down to fit a smaller object? what method sets the mode? BASE_LEVEL_POINT (FASTEST) can produce shimmering effects as object is moved? BASE_LEVEL_FILTER removes shimmering unless image is minified a lot MULTI_LEVEL_POINT MULTI_LEVEL_LINEAR as BASE modes, if texture is loaded with a MIPMAP setMinFilter(int filterMode) what options are available that effect how a texture is scaled up to fit a larger object? what method sets the mode? BASE_LEVEL_POINT (FASTEST) sets pixel colour using texel closest to texture coordinates BASE_LEVEL_LINEAR (NICEST) uses weighted average of 2x2 array of texels around texture coordinate setMagFilter(int filterMode); what are the boundary modes for textures? what methods set the mode in X, Y axes (relative to texture) WRAP image repeats outside [0, 1] range CLAMP colour value at boundary is extended to boundary of object (ehh) setBoundaryModeS(mode); setBoundaryModeT(mode); what conditions must be true for texture mapping to be enabled? 1. shape has texture coordinates 2. appearance has a Texture associated with it 3. the Texture is enabled -> texture.setEnable(true); supply example code loading a texture into a Texture2D object TextureLoader texLoader = new TextureLoader("images/stone1.png", null); Texture2D texture = (Texture2D)texLoader.getTexture(); is the observer parameter (second constructor argument to TextureLoader) necessary? apparently not... can pass in null. name the one TextureLoader flags parameter supplied in the notes? what does it do? GENERATE_MIPMAP allows textures to be selectively used at a variety of scales what appearance component controls how a texture is applied to a surface? TextureAttributes what appearance component controls the texture image? Texture. Duh. what are the bounds of texture coordinates? from 0,0 -> bottom left corner to 1,1 -> top right corner what is the range of Material shininess? what is the default value? 1-128f, higher being shinier. default value is 64f what determines the intensity of diffuse lighting? the angle the light ray makes with the surface of the object. greatest when light ray hits surface directly what types of lighting is a Material composed from? what is the scalar parameter associated with a Material? ambient emissive diffuse specular ... float shininess what conditions are necessary for lighting to effect the colour of a shape? if not, what determines the colour? 1. the geometry for the shape has normals 2. the appearance has a Material 3. the Material enables lighting If unsatisfied, colour is determined from ColorAttributes. describe the two transparency modes available in the TransparencyAttributes class? SCREEN_DOOR checkerboard pattern, percentage of transparent pixels is defined by tValue specified in constructor BLENDED blend equation defined by source and dest blend function. default is alpha(src) * src + (1 - alpha(src)) * dst what is the default polygon culling mode? PolygonAttributes.CULL_NONE what does the backFaceNormalFlip switch do in the PolygonAttributes class? enables rendering the back of a surface with specular or diffuse light name the three polygon modes PolygonAttributes .POLYGON_POINT .POLYGON_LINE .POLYGON_FILL write a code excerpt creating a flat shaded red sphere Sphere ball = new Sphere(); Appearance app = new Appearance(); Color3f red = new Color3f(1f, 0f, 0f); ColoringAttributes colourAttribs = new ColoringAttributes(red, ColoringAttributes.SHADE_FLAT); app.setColoringAttributes(colourAttribs); ball.setAppearance(app); what two parameters does the ColoringAttributes constructor take, and what are the options in the second parameter? colour, shading model shading model is: SHADE_FLAT -> use last vertex colour SHADE_GOURAUD -> interpolate across surface NICEST / FASTEST what package provides the Color3f class? javax.vecmath write a loader example that imports a scene from a Wavefront (obj) file and returns it as a BranchGroup. public BranchGroup importScene() { java.net.URL url = "http://www.dcu.ie/scene.obj"; ObjectFile f = new ObjectFile(ObjectFile.RESIZE); Scene s = null; try { s = f.load(url); } catch(Exception e) { throw new ImportFailedException( "Couldn't load model " + e.getMessage()); } return s.getSceneGroup(); } what are the main appearance attributes? colouring (selection, shading) point (size, antialiasing) line (width, pattern) polygon (culling, rasterisation mode) rendering (depth buffer, rubber banding) transparency material texture image texture attribs? texcoord generation textureUnitState what is the shape Primitive Cone's constructor? Cone(float radius, float height, int flags, int xDivisions, int yDivisions, Appearance app); create a geometryinfo for a quad array. assuming the vertices and indices are stored in arrays pts and indices respectively, write code to create a GeometryArray using NormalGenerator to... generate... normals at a 45 degree angle. GeometryInfo gi = new GeometryInfo( GeometryArray.QUAD_ARRAY); ... gi.setCoordinates(pts); gi.setCoordinateIndices(indices); NormalGenerator ng = new NormalGenerator(); ng.setCreaseAngle((float)Math.toRadians(45)); ng.generateNormals(gi); GeometryArray cube = gi.getGeometryArray(); use Triangulator and GeometryInfo to create a triangle with a hole in the middle int[] stripCounts = new int[]{3, 3}; int[] contourCounts = new int[]{2}; Point3f[] pts = new Point3f[6]; pts[0] = new Point3f(-1f, -1f, 0f); pts[1] = new Point3f(1f, -1f, 0f); pts[2] = new Point3f(1f, 1f, 0f); pts[3] = new Point3f(-0.5f, -0.5f, 0f); pts[4] = new Point3f(0.5f, -0.5f, 0f); pts[5] = new Point3f(0.5f, 0.5f, 0f); GeometryInfo gi = new GeometryInfo(GeometryInfo.POLYGON_ARRAY); gi.setCoordinates(pts); gi.setStripCounts(stripCounts); gi.setContourCounts(contourCounts); Triangulator tr = new Triangulator(); tr.triangulate(gi); GeometryArray triangleWithHole = gi.getGeometryArray(); what methods does NormalGenerator provide to get the job done? setCreaseAngle((float)Math.toRadians(30)); generateNormals(GeometryInfo); what method does Triangulator provide to do the job? triangulate(GeometryInfo) how do we define a LineStripArray with two strips, one with 2 vertices and the other with 3? int[] stripLengths = new int[]{2, 3}; LineStripArray lsa = new LineStripArray(5, LineArray.COORDINATES, stripLengths); what tool classes does GeometryInfo provide, and what do they generate? Triangulator NormalGenerator Stripifier, and they all generate a GeometryArray create a cube from an IndexedQuadArray Point3f[] pts = new Point3f[8]; pts[0] = new Point3f(-1f, -1f, 1f); pts[1] = new Point3f(1f, -1f, 1f); pts[2] = new Point3f(-1f, 1f, 1f); pts[3] = new Point3f(1f, 1f, 1f); pts[4] = new Point3f(-1f, -1f, -1f); pts[5] = new Point3f(1f, -1f, -1f); pts[6] = new Point3f(-1f, 1f, -1f); pts[7] = new Point3f(1f, 1f, -1f); // define faces (quads) int[] coordIndices = { 0, 1, 2, 3, // front 0, 2, 4, 6 // left 1, 3, 5, 7 // right 4, 5, 6, 7 // back 0, 1, 4, 5 // bottom 2, 3, 6, 7 // top }; IndexedQuadArray iqa = new IndexedQuadArray(8, GeometryArray.COORDINATES); iqa.setCoordinates(0, pts); iqa.setCoordinateIndices(0, coordIndices); create a simple PointArray with 3 vertices PointArray pa = new PointArray(3, PointArray.COORDINATES); Point3f[] points = new Point3f[3]; points[0] = new Point3f(0f, 0f, 1f); points[1] = new Point3f(0f, 1f, 0f); points[2] = new Point3f(1f, 0.5f, 0.5f); pa.setCoordinates(0, points); what is the top node of a Java3D scene graph? the virtual universe, which represents the 3D space Name all the basic GeometryArrays? PointArray LineArray TriangleArray QuadArray LineStripArray TriangleStripArray TriangleFanArray a TriangleArray is created like so: TriangleArray ta = new TriangleArray(3, TriangleArray.COORDINATES | TriangleArray.COLOR_3 | TriangleArray.NORMALS); How do we set the corresponding vertex values (to predictably named arrays)? ta.setCoordinates(0, points); ta.setColors(0, colours); ta.setNormals(0, normals); define a Java3D point (of floats) at 1.0, 1.0, 1.0. Point3f point = new Point3f(1.0f, 1.0f, 1.0f); what Java3D package provides the Point3d, Color4b and Vector3f classes? javax.vecmath what is important about the order of vertices in 2D geometries? the normal defines the "front" of the surface, and vertices are ordered counter-clockwise around the normal apart from a location coordinate, what other coordinates can a vertex contain? normals colours texture what are the primitive geometry types built from? vertices how do we adjust the viewing platform automatically to see most of the objects in the scene easily? universe.getViewingPlatform() .setNominalViewingTransform() how are Geometries associated with Shape3D objects? references stored in a list in the Shape3D how can a Branch or SharedGroup be optimised before making it live? by calling the compile() method what is the root node of a branch graph? BranchGroup give an example of setting a capability bit tg.setCapability(TransformGroup .ALLOW_TRANSFORM_WRITE); how do we tell Java3D that an element of a live scene can be changed? capability bits... name the 4 important environment node types (according to the notes)? Light Background Fog Behavior (bloody Americans) name the high-level steps in creating a simple Java3D program 1. Create a Canvas3D to display the scene 2. Create a SimpleUniverse to contain/manage the scene graph 3. Attach Canvas3D to SimpleUniverse (passed to SimpleUniverse constructor) 4. Create content branch to describe scene and connect to SimpleUniverse