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OpenGL CS418 Computer Graphics John C. Hart. OpenGL Based on GL (graphics library) by Silicon Graphics Inc. (SGI) Advantages: Runs on everything, including.

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Presentation on theme: "OpenGL CS418 Computer Graphics John C. Hart. OpenGL Based on GL (graphics library) by Silicon Graphics Inc. (SGI) Advantages: Runs on everything, including."— Presentation transcript:

1 OpenGL CS418 Computer Graphics John C. Hart

2 OpenGL Based on GL (graphics library) by Silicon Graphics Inc. (SGI) Advantages: Runs on everything, including cell phones (OpenGL/ES) Alternatives: Microsoft’s Direct3D – limited to MSWindows Sun’s Java3D – slower, implemented on top of OpenGL

3 APP GLUT Library Layers OpenGL = GL + GLU –Basic low-level GL routines implemented using OS graphics routines –Timesaving higher-level GLU routines implemented using GL routines GLUT opens and manages OpenGL windows and adds helper functions OpenGL Extensions provide direct device-dependent access to hardware GL GLU OS Driver HW EXT

4 Vertex Pipeline Homogeneous Divide Model Coords Model Xform World Coords Viewing Xform Still Clip Coords Clipping Window Coordinates Window Coordinates Window to Viewport Window to Viewport Coordinates Viewport Coordinates Clip Coords Viewing Coords Perspective Distortion

5 Viewport Coordinates Physical per-pixel integer coordinates Also called screen or device coordinates glViewport(x,y,w,h) x,y – lower left pixel w – width h – height Sometimes (0,0) is in the upper left corner (e.g. for mouse input) (0,0)(HRES-1,0) (HRES-1, VRES-1) (0,VRES-1)

6 Window Coordinates Logical, mathematical floating-point coordinates glOrtho(l,r,b,t,n,f) left, right, bottom, top near, far: limits depth gluOrtho2D(l,r,b,t) calls glOrtho(l,r,b,t,-1,1) To use per-pixel coordinates, call: gluOrtho2D(-.5,-.5,w-.5,h-.5); (-1,-1)(1,-1) (1,1) (-1,1)

7 OpenGL State OpenGL commands change its internal state variables which control how it turns geometric models into pictures E.g. the window-to-viewport transformation glViewport(x,y,w,h) glOrtho(l,r,b,t,n,f) Can query this state: GLfloat buf[4]; glGetFloatv(GL_VIEWPORT,buf); x = buf[0]; y = buf[1]; w = buf[2]; h = buf[3]; (l,b)(r,b) (r,t)(l,t) (x,y)(x+w-1,y) (x+w-1,y+h-1) (x,y+h-1) W2V OpenGL State: x,y,w,h,l,r,b,t,n,f,…

8 OpenGL Commands gl[u]Fubar[234][dfis][v] [u]: GLU v. GL command [234]: dimension [dfisb]: data type –d: GLdouble (double) –f: GLfloat (float) –i: GLint (int) –s: string [v]: vector (reference v. value) Examples: glVertex3f(-0.5, 3.14159, 2); glVertex2i(200, 350); GLdouble point[4]; glVertex4dv(point); Examples: glVertex3f(-0.5, 3.14159, 2); glVertex2i(200, 350); GLdouble point[4]; glVertex4dv(point);

9 Points glBegin(GL_POINTS); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

10 Lines glBegin(GL_LINES); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

11 Line Strip glBegin(GL_LINE_STRIP); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

12 Line Loop glBegin(GL_LINE_LOOP); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

13 Polygon glBegin(GL_POLYGON); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1) OpenGL only supports convex polygons (and really only triangles)

14 Quads glBegin(GL_QUADS); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

15 Quads glBegin(GL_QUADS); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glEnd(); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.);

16 Quads glBegin(GL_QUADS); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glEnd(); (-1,1) (-1,-1)(1,-1) (1,1) (-1,1) Lines should never pass through a vertex.

17 Triangles glBegin(GL_TRIANGLES); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

18 Triangles glBegin(GL_TRIANGLES); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.6,1.); glVertex2f(-.2,.6); glVertex2f(.6,1.); glVertex2f(-.2,.6); glVertex2f(.2,.6); glVertex2f(.6,1.); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); … glEnd(); (-1,-1)(1,-1) (1,1) (-1,1) Lines should never pass through a vertex.

19 Triangle Strip glBegin(GL_TRIANGLE_STRIP); glVertex2f(-.6,1.); glVertex2f(-.6,.6); glVertex2f(-.2,.6); glVertex2f(-.2,-.6); glVertex2f(-.6,-.6); glVertex2f(-.6,-1.); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glVertex2f(.2,-.6); glVertex2f(.2,.6); glVertex2f(.6,.6); glVertex2f(.6,1.); glEnd(); (-1,-1)(1,-1) (1,1) (-1,1)

20 Triangle Strip glBegin(GL_TRIANGLE_STRIP); glVertex2f(-.6,1.); glVertex2f(.6,1.); glVertex2f(-.2,.6); glVertex2f(.2,.6); glVertex2f(-.2,-.6); glVertex2f(.2,-.6); glVertex2f(.6,-1.); glVertex2f(.6,-.6); glEnd(); … (-1,-1)(1,-1) (1,1) (-1,1) First two vertices prime the pump, then every new vertex creates a triangle connecting it to the previous two vertices

21 Triangle Fan glBegin(GL_TRIANGLE_FAN); glVertex2f(-.2,.6); glVertex2f(-.6,.6); glVertex2f(-.6,1.); glVertex2f(.6,1.); glVertex2f(.2,.6); glVertex2f(.2,-.6); glVertex2f(-.2,-.6); glEnd(); … (-1,-1)(1,-1) (1,1) (-1,1) First two vertices prime the pump, then every new vertex creates a triangle connecting it to the previous vertex and the first vertex

22 Assigning Color glColor3f(0,0,1); glBegin(GL_POLYGON); glVertex2f(-1,1); glVertex2f(-1,-1); glVertex2f(1,-1); glEnd(); glColor3f(1,0,0); glBegin(GL_POLYGON); glVertex2f(-1,1); glVertex2f(-1,-1); glVertex2f(1,-1); glEnd(); glColor3f(0,0,0); glBegin(GL_LINE_LOOP); glVertex2f(-1,1); glVertex2f(-1,-1); glVertex2f(1,-1); glEnd(); glBegin(GL_POLYGON); glColor3f(0,1,0); glVertex2f(-1,1); glColor3f(0,0,1); glVertex2f(-1,-1); glColor3f(1,0,0); glVertex2f(1,-1); glEnd();

23 Indexed Face Set Popular file format –VRML, Wavefront “.obj”, etc. Ordered list of vertices –Prefaced by “v” (Wavefront) –Spatial coordinates x,y,z –Index given by order List of polygons –Prefaced by “f” (Wavefront) –Ordered list of vertex indices –Length = # of sides –Orientation given by order v x 1 y 1 z 1 v x 2 y 2 z 2 v x 3 y 3 z 3 v x 4 y 4 z 4 f 1 2 3 f 2 4 3 (x1,y1,z1)(x1,y1,z1) (x2,y2,z2)(x2,y2,z2) (x3,y3,z3)(x3,y3,z3) (x4,y4,z4)(x4,y4,z4)

24 Other Attributes Vertex normals –Prefixed w/ “vn” (Wavefront) –Contains x,y,z of normal –Not necessarily unit length –Not necessarily in vertex order –Indexed as with vertices Texture coordinates –Prefixed with “vt” (Wavefront) –Not necessarily in vertex order –Contains u,v surface parameters Faces –Uses “/” to separate indices –Vertex “/” normal “/” texture –Normal and texture optional –Can eliminate normal with “//” v x 0 y 0 z 0 v x 1 y 1 z 1 v x 2 y 2 z 2 vn a 0 b 0 c 0 vn a 1 b 1 c 1 vn a 2 b 2 c 2 vt u 0 v 0 vt u 1 v 1 vt u 2 v 2 (x 0,y 0,z 0 ) (a 0,b 0,c 0 ) (u 0,v 0 ) (x1,y1,z1)(a1,b1,c1)(u1,v1)(x1,y1,z1)(a1,b1,c1)(u1,v1) (x2,y2,z2)(a2,b2,c2)(u2,v2)(x2,y2,z2)(a2,b2,c2)(u2,v2) f 0/0/0 1/1/1 2/2/2f 0/0/0 1/0/1 2/0/2

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