4 pipeline computer graphics

4 pipeline computer graphics

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  3/4/2019 1 SBE 306: ComputerGraphics Pipeline Dr. Ayman Eldeib Systems & Biomedical Engineering Department Spring 2019 Computer Graphics Pipeline Graphical Information Flow Transform Illuminate Transform Clip Project Rasterize Model & Camera Parameters Rendering Pipeline Framebuffer Display A memory array in which the computer stores an image
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  3/4/2019 2 Computer Graphics Pipeline There are two pipelines:  The upper pipeline – Geometric Primitives o Vertex-based primitives – points, lines and polygons  The lower pipeline – Image Primitives o Pixel-based primitives – image and bitmaps  These two separate pipelines are linked through texture mapping Cont. Graphical Information Flow Computer Graphics Pipeline Rendering Pipeline Spring 2011 Modeling Transforms 3D geometry Primitives Lighting Calculations Viewing Transform Clipping Projection Transform Scan Conversion Image Transform into 3D world coordinate system Transform into 3D camera coordinate system Draw pixels (includes texturing, hidden surface, ...) Clip primitives outside camera’s view Transform into 2D screen coordinate system Illuminate according to lighting and reflectance
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  3/4/2019 3 Computer Graphics Pipeline Spring2011 Modeling Transforms 3D geometry Primitives Lighting Calculations Viewing Transform Clipping Projection Transform Scan Conversion Image  Model/view transforms combined  Really “vertices” not “primitives” Making this the vertex pipeline  There’s a lot going on in the “scan conversion” stage! [pixel or fragment pipeline] Primitive assembly Rasterization Texture mapping Per-pixel lighting Visibility (Z-buffer) For an OpenGL system Cont. Rendering Pipeline Computer Graphics Pipeline Graphical Information Flow GPUCPU Application Vertex Processor & Rasterization Assembly & Rasterization Pixel Processor Vertices (3D) Vertices (2D) Fragments (pre-pixels) Final pixels (Color, Depth) Graphics State Render-to-texture Application Geometry “vertex pipeline” Rasterization “pixel/fragment pipeline” Handle input, Simulation & AI, etc. Transform, Lighting, Calculate texture coords, etc. fill pixels, Interpolate vertex parameters, Look up/filter textures, etc. Video Memory (Textures)
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  3/4/2019 4 Computer Graphics Pipeline OpenGLand Related APIs  Computer Graphics Pipeline OpenGL: Application Structure Basics  Configure and open window  Initialize OpenGL state  Register input callback functions  Render  Resize  Input: keyboard, mouse, etc  Enter event processing loop
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  3/4/2019 5 Computer Graphics Pipeline Modeling:The Basics  Common interactive 3-D primitives: points, lines, polygons (i.e., triangles)  Organized into objects  Collection of primitives, other objects  Associated matrix for transformations  Instancing: using same geometry for multiple objects  4 wheels on a car, 2 arms on a robot Computer Graphics Pipeline Modeling: The Scene Graph  The scene graph captures transformations and object- object relationships  Maintain a matrix stack of transformations  Nodes are objects;  Arrows indicate instancing Each has a matrix Robot BodyHead ArmTrunkLegEyeMouth
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  3/4/2019 6 Computer Graphics Pipeline Rendering:Transformation  There are three set of transformation: Modeling transforms o Size, place, scale, and rotate objects parts o Object coordinates  world coordinates Viewing transforms o Rotate & translate the world to lie directly in front of the camera Typically place camera at origin Typically looking down -Z axis oWorld coordinates  view coordinates Projection transforms o Apply perspective foreshortening o View coordinates  screen coordinates Computer Graphics Pipeline OpenGL: 3D Coordinate System Left handed Right handed OpenGL uses a right handed coordinate system
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  3/4/2019 7 Computer Graphics Pipeline OpenGL has a model view matrix that is applied to each point (vertex)  You can alter the current model view matrix by calling a transformation function  This applies the transformation to all points drawn after the transformation call OpenGL: Modeling Computer Graphics Pipeline Viewing: Camera Movement
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  3/4/2019 8 Computer Graphics Pipeline OpenGL:Camera Movement  In OpenGL the last transformation defined is the first one applied  To move the camera a transformation must be applied to all scene points  Thus a transformation that moves the camera should be the first transformation applied Cont. Computer Graphics Pipeline OpenGL: Camera Frame • gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz) • Camera is at eye, looking at center, with the up direction being up Eye Up vector (u) Center -Z YX V vector (v)
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  3/4/2019 9 Computer Graphics Pipeline OpenGL:Specifying Viewpoint  glMatrixMode(GL_MODELVIEW);  glLoadIdentity();  gluLookAt(eyeX, eyeY, eyeZ, lookX, lookY, lookZ, upX, upY, upZ);  eye[XYZ]: camera position in world coordinates  look[XYZ]: a point centered in camera’s view  up[XYZ]: a vector defining the camera’s vertical  Creates a matrix that transforms points in world coordinates to camera coordinates  Camera at origin  Looking down -Z axis  Up vector aligned with Y axis (actually Y-Z plane) Computer Graphics Pipeline OpenGL: Camera Movement gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz) Camera is at eye, looking at center, with the up direction being up  First, create a coordinate frame for the camera The look vector is center minus eye Then use cross product with up vector  Define a rotation matrix  Apply appropriate translation for camera (eye) location
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  3/4/2019 10 Computer Graphics Pipeline OpenGL:Camera Example Crystal Ball Interface  Allow the user two options perhaps using the left-right and up-down arrow keys 1. Rotate about the vertical direction in the window 2. Rotate about the horizontal direction in the window Computer Graphics Pipeline  Eye position – location of camera center (ex,ey,ez)  Look vector – direction camera is looking w vector  Up vector – the vertical direction for the camera u vector  V is horizontal direction for the camera Cont. OpenGL: Camera Example Crystal Ball Interface
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  3/4/2019 11 Computer Graphics Pipeline Rotate about the vertical direction in the window Rotate the eye position about the up vector The up vector and the center point remain fixed  Rotate about the horizontal direction in the window Compute the current horizontal direction from the up vector and the look vector Rotate the eye about the horizontal direction Rotate the up vector about the horizontal direction OpenGL: Camera Example Crystal Ball Interface Cont. g{tÇ~ lÉâg{tÇ~ lÉâg{tÇ~ lÉâg{tÇ~ lÉâ