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©Zachary Wartell, UNCC9/28/2006 11:30 AM 1 Overview of OpenGL Revision: 1.2 Copyright Professor Zachary Wartell, University of North Carolina All Rights.

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Presentation on theme: "©Zachary Wartell, UNCC9/28/2006 11:30 AM 1 Overview of OpenGL Revision: 1.2 Copyright Professor Zachary Wartell, University of North Carolina All Rights."— Presentation transcript:

1 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 1 Overview of OpenGL Revision: 1.2 Copyright Professor Zachary Wartell, University of North Carolina All Rights Reserved

2 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 2 Graphics APIs Generally these API’s support both 2D and 3D graphics: ●GKS (Graphics Kernal System) ●PHIGS (Programmer Hierarchical Interactive Graphics Standard) ●PHIGS+ ●GL (Graphics Library) by SGI ●OpenGL ●DirectDraw, Direct3D by Microsoft

3 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 3 OpenGL ●OpenGL – hardware independent, only specifies graphics output low level, no GUI operations (events, windows, menu’s) ●OpenGL Utility (GLU) – higher level graphics primitives (spheres, curves, curved surfaces) ●OpenGL Utility Toolkit (GLUT) – primitive window setup & event handling

4 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 4 OpenGL Block Diagram input commands –vertex coordinates and vertex attributes –pixel blocks –state changes (affects how input data is rendered) output commands –read current state, read framebuffer, etc. commands

5 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 5 OpenGL Basic Syntax (C Language Binding) ●Functions: glXXXX – glBegin, glEnd, glPolygonMode ●Constants: GL_XXXX – GL_2D, GL_RGB, GL_CCW ●Types: GLxxx – GLbyte, GLshort, GLint, GLfloat, GLdouble, GLboolean

6 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 6 OpenGL Geometric Output Primitives ●Types: GL_POINTS, GL_LINES, GL_LINE_LOOP, GL_LINE_STRIP, GL_POLYGON, GL_QUADS, GL_QUAD_STRIP, GL_TRIANGLE, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN ●Basic Syntax: glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); glVertex(2|3|4)(s|i|d|f)[v]

7 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 7 OpenGL: A State Machine OpenGL state remains in effect until it is changed Examples: current - color, viewing/projection transforms, line/polygon fill pattern, light positions, etc, etc, etc.. Each state variable has default value and can be queried (glGetIntegerv, glGetFloatv, etc.) and enabled/disable collections of state can also be saved (glPushAttrib,glPopAttrib) commands

8 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 8 Display Lists immediate vs retained mode display list can collect geometry and attributes to be stored for later use; allows optimizations display list are write-only; no other structure within objects (OpenInventor, Java3D, VRML, etc.) commands

9 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 9 Evaluators (3D stuff) a set of functions that generates vertex coordinates lying on various types of curves surfaces uses polynomial mapping. Can produce surface normals, texture coordinates, colors, vertex coordinates given a set of control points commands

10 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 10 Per-Vertex Operations vertices are transformed by 4x4 matrices (model&view, projection) in preparation for primitive assembly texture coordinates can be directly specified or generated and also transformed lighting calculations are also performed with transformed vertex and normals based on lighting attributes commands

11 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 11 Primitive Assembly points, lines, polygon edges are clipped and transformed to window coordinates resulting primitives are then passed to rasterization stage commands

12 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 12 Points & Lines v0 v1 v2 v3 glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); v0 v1 v2 v3 v4 v5 GL_POINTS GL_LINES GL_LINE_STRIP v0 v1 v2 v3 v4 GL_LINE_LOOP

13 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 13 Polygons glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); GL_POLYGON v0 v1 v2 v3 v4 v0 v1 v2 v3 v4 v5 v6 v7 GL_QUADS v0 v1 v2 v3 v4 v5 v6 v7 GL_QUAD_STRIP

14 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 14 ©Zachary Wartell - 1/26/2005 Polygons (2) glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); v0 v1 v2 v3 v4 v5 GL_TRIANGLES GL_TRIANGLE_STRIP v0 v1 v2 v3 v4 v5 GL_TRIANGLE_FAN v0 v1 v2 v3 v4 v5 N vertices N/3 Triangles N+2 vertices N Triangles N+2 vertices N Triangles

15 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 15 Why glBegin/glEnd? ● trying to define a separate function for each possible combinations of vertex data too cumbersome: glBegin (PrimitiveConstant); glColor3f (c1,c1,c1) glTexCoord2f(t1,t2) glVertex3f (x1,y1,z1) glColor3i (c1,c2,c3) glNormal3f (n1,n2,n3) glVertex3f (x2,y2,z2) …. glEnd(); -vertex uses last specified color/normal/texCoord. Allows application to avoid redundant specification, but every app. may want different combinations -Also lots of combinations of (s|i|f|d)[v] especially when combined with all possible combinations of glColor ×glTexCoord × glNormal × glVertex

16 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 16 Why glBegin/glEnd? ● allow maximum possible parallelism in host CPU and Graphics Processor glBegin (PrimitiveConstant); compute x1,y1,z1 coordinate glVertex3f (x1,y1,z1) compute x2,y2,z2 coordinate glVertex3f (x2,y2,z2) …. glEnd(); CPU to GP communication and GP processing of x1,y1,z1 can potentially occur while CPU does this

17 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 17 Vertex Arrays ● downside of glBegin/glEnd is lots of function calls ●OpenGL Vertex Arrays -drastically reduce function call overhead -support most common combinations of vertex data -allow sharing of vertex coordinates for adjacent primitives glEnableClientState (GL_VERTEX_ARRAY); glVertexPointer ( 3 /* N-coordinates */, GL_FLOAT /* coordinate type */, 0 /* stride */, vertex_coordinates); glDrawElements (GL_QUADS /* primitive type */, 24, /* number of vertices */ GL_UNSIGNED_BYTE, /* type of index value */ vertex_indices ); -void* parameter, actual type determined by 3 rd parameter

18 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 18 Pixel Operations pixels packed or unpacked into RGB(A) components; also may be scaled, biased or transformed results are clamped and sent to texture memory OR rasterization pixel data also can be read from framebuffer commands

19 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 19 Pixel-Array Primitives glBitmap (width, height, x0, y0, xOffset, yOffset, bit_array) ● width, height - size of bit map to draw (in last specified color) ●x0, y0 – defines window coordinate of lower-left corner of bit_array ● xOffset, yOffset – added to current raster position (see glRasterPos2i); useful for text output ● bit_array – bits encode in unsigned byte array

20 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 20 glBitmap Figure 3-61: Hearn & Baker

21 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 21 glDrawPixels glDrawPixels (width, height, dataFormat, dataType, pixel_array) ● width, height - size of pixel array map to draw ●dataFormat – GL_RGB,GL_RED, GL_RGBA, GL_DEPTH_COMPONENT, etc. ●dataType – GL_UNSIGNED_BYTE, GL_BYTE, etc. ●pixel_array – memory encoding data -data write to current raster position (glRasterPos)

22 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 22 OpenGL Raster Operations ●raster operations, bitblt’s (bit-block transfers), pixblt’s ● glReadPixels (xmin, ymin, width, height, dataFormat, dataType, pixel_array) -reads pixel data from framebuffer to main memory -xmin, ymin, width, height – rectangle in framebuffer to read -dataFormat – GL_RGB,GL_RED, GL_RGBA, GL_DEPTH_COMPONENT, etc. -dataType – GL_UNSIGNED_BYTE, GL_BYTE, etc. -pixel_array – memory encoding data ●glCopyPixels – from glReadBuffer to glDrawBuffer

23 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 23 Texture Assembly Textures (images + lots of texture rendering options) can be bound to texture objects; then you can switch between texture objects Multiple textures layers commands

24 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 24 Rasterization scan convert coordinate primitives (lines, polygons, etc.) or pixel data into fragments fragment is pixel color + depth value + stencil + accumulation commands

25 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 25 Fragment Operations sequence of operations that may discard fragment blending, dithering, logic combination (and/or/xor) commands

26 ©Zachary Wartell, UNCC9/28/2006 11:30 AM 26 Revisions Revision 1.1: 1.typos 2.Added copyright 3.formatted master Slide 1.Revision 1.2 1.added GL pipeline slides

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