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OpenGL Tutorial CISC 640/440 Computer Graphics

OpenGL Tutorial CISC 640/440 Computer Graphics. TA: Qi Li/Mani Thomas qili@cis.udel.edu / manivt@cis.udel.edu. OpenGL: What is It?. GL ( G raphics L ibrary): Library of 2-D, 3-D drawing primitives and operations API for 3-D hardware acceleration

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OpenGL Tutorial CISC 640/440 Computer Graphics

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  1. OpenGL Tutorial CISC 640/440 Computer Graphics TA: Qi Li/Mani Thomas qili@cis.udel.edu/manivt@cis.udel.edu CISC640/440 OpenGL Tutorial

  2. OpenGL: What is It? • GL (Graphics Library): Library of 2-D, 3-D drawing primitives and operations • API for 3-D hardware acceleration • GLU (GL Utilities): Miscellaneous functions dealing with camera set-up and higher-level shape descriptions • GLUT (GL Utility Toolkit): Window-system independent toolkit with numerous utility functions, mostly dealing with user interface CISC640/440 OpenGL Tutorial

  3. GL_LINES GL_POLYGON GL_LINE_STRIP GL_LINE_LOOP GL_POINTS GL_TRIANGLES GL_QUADS GL_TRIANGLE_FAN GL_TRIANGLE_STRIP GL_QUAD_STRIP OpenGL Geometric Primitives CISC640/440 OpenGL Tutorial

  4. Specifying Geometric Primitives • Primitives are specified using glBegin(primType); ... glEnd(); • primType determines how vertices are combined • GLfloat red, green, blue; • GLfloat x, y; • glBegin(primType); • for (i = 0; i < nVerts; i++) { • glColor3f(red, green, blue); • glVertex2f(x, y); • ... // change coord. values • } • glEnd();

  5. OpenGL Vertex/Color Command Formats glVertex3fv( v ) glColor3fv( v ) Data Type Vector Number of components b - byte ub - unsigned byte s - short us - unsigned short i - int ui - unsigned int f - float d - double omit “v” for scalar form– e.g., glVertex2f(x, y) glColor3f(r, g, b) 2 - (x,y) 3 - (x,y,z), (r,g,b) 4 - (x,y,z,w), (r,g,b,a)

  6. OpenGL 3-D coordinates • Right-handed system • From point of view of camera looking out into scene: • +X right, -X left • +Y up, -Y down • +Zbehind camera, -Z in front • Positive rotations are counterclockwise around axis of rotation CISC640/440 OpenGL Tutorial

  7. Transformations in OpenGl • Modeling transformation • Viewing transformation • Projection transformation CISC640/440 OpenGL Tutorial

  8. Modeling Transformation • Refer to the transformation of models (i.e., the scenes, or objects) • Generally, • glMultMatrixf(M_i) • Some simple transformations • Translation: glTranslate(x,y,z) • Scale: glScale(sx,sy,sz) • Rotation: glRotate(theta, x,y,z) • x,y,z are components of vector defining axis of rotation • Angle in degrees; direction is counterclockwise CISC640/440 OpenGL Tutorial

  9. Viewing Transformation • Refer to the transformation on the camera • Using glTranslate*() and glRotate*() • Using gluLookAt() • gluLookAt (eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) • eye= (eyeX, eyeY, eyeZ)T: Desired camera position • center = (centerX, centerY, centerZ)T: Where camera is looking • up = (upX, upY, upZ)T: Camera’s “up” vector CISC640/440 OpenGL Tutorial

  10. Viewing Transformation from Woo et al CISC640/440 OpenGL Tutorial

  11. Projection Transformation • Refer to the transformation from scene to image • Orthographic projection • glOrtho (left, right, bottom, top, near, far) from Hill CISC640/440 OpenGL Tutorial

  12. Projection Transformation • Refer to the transformation from scene to image • Orthographic projection • glOrtho (left, right, bottom, top, near, far) • Perspective projection • glFrustum (left, right, bottom, top, near, far) CISC640/440 OpenGL Tutorial

  13. Projection Transformation • Refer to the transformation from scene to image • Orthographic projection • glOrtho (left, right, bottom, top, near, far) • Perspective projection • glFrustum (left, right, bottom, top, near, far) CISC640/440 OpenGL Tutorial

  14. Notes on openGl transformations • Before applying modeling or viewing transformations, need to set glMatrixMode(GL_MODELVIEW) • Before applying projection transformations, need to set glMatrixMode(GL_Projection) • Replacement by either following commands glLoadIdentity(); glLoadMatrix(M); • Multiple transformations (either in modeling or viewing) are applied in reverse order CISC640/440 OpenGL Tutorial

  15. Notes on openGl transformations • Before applying modeling or viewing transformations, need to set glMatrixMode(GL_MODELVIEW) • Before applying projection transformations, need to set glMatrixMode(GL_Projection) • Replacement by either following commands glLoadIdentity(); glLoadMatrix(M); • Multiple transformations (either in modeling or viewing) are applied in reverse order CISC640/440 OpenGL Tutorial

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