![Viewport
In addition, we define a rectangular viewport in the screen window on the
display.
A mapping (consisting of scalings [changesize] and translations [move
object]) between the world window and the viewportis established by
OpenGL.
The objects inside the world window appear automatically at proper sizes
and locations inside the viewport(in screencoordinates, which arepixel
coordinates on the display).
void setViewport(GLintleft, GLint right, GLint bottom, GLint top)
{
glViewport(left, bottom, right - left, top - bottom);
}
Calls: setWindow(-5.0,5.0, -0.3, 1.0);
o setViewport(0, 640, 0, 480);
In myInit();
We use natural coordinates for whatwe are drawing (the world window).
OpenGL converts our coordinates to screen coordinates when we set up a
screen window and a viewport. The viewportmay be smaller than the
screen window. The default viewportis the entire screen window.
The conversion requires scaling and shifting: mapping the world window to
the screen window and the viewport.
Windows aredescribed by their left, top, right, and bottom values,
w.l,
w.t,
w.r,
w.b.
Viewports aredescribed by the samevalues but in screen window
coordinates.
v.l,
v.t,
v.r,
v.b,](https://image.slidesharecdn.com/computergraphics-170824045331/85/computer-graphics-slides-by-Talha-shah-2-320.jpg)
computer graphics slides by Talha shah
- 1. glOrtho The glOrtho function describes a perspective matrix that produces a parallel projection. The (left, bottom, near) and (right, top, near) parameters specify the points on the near clipping plane that are mapped to the lower-left and upper-rightcorners of the window, respectively, assuming that the eye is located at (0, 0, 0). The far parameter specifies the location of the far clipping plane. Both the near and the far can be either positive or negative. Because OpenGL uses matrices to set up all its transformations, thecall to gluOrtho2D() mustbepreceded by two setup functions: glMatrixMode(GL_PROJECTION); glLoadIdentity(); //toreset the matrix World Window The space in which objects are described is called world coordinates (the numbers used for x and y are those in the world, wherethe objects are defined). World coordinates use the Cartesian xy-coordinatesystemused in mathematics, based on whatever units are convenient. We define a rectangular worldwindow in these world coordinates. The world window specifies which part of the world should be drawn: whichever part lies inside the window should be drawn, and whichever part lies outside should be clipped away and not drawn. OpenGL does the clipping automatically. The function setWindow sets the world window size: void setWindow(GLdoubleleft, GLdouble right, GLdouble bottom, GLdouble top) { glMatrixMode(GL_PROJECTION); o glLoadIdentity(); o gluOrtho2D(left, right, bottom, top); }
- 2. Viewport In addition, we define a rectangular viewport in the screen window on the display. A mapping (consisting of scalings [changesize] and translations [move object]) between the world window and the viewportis established by OpenGL. The objects inside the world window appear automatically at proper sizes and locations inside the viewport(in screencoordinates, which arepixel coordinates on the display). void setViewport(GLintleft, GLint right, GLint bottom, GLint top) { glViewport(left, bottom, right - left, top - bottom); } Calls: setWindow(-5.0,5.0, -0.3, 1.0); o setViewport(0, 640, 0, 480); In myInit(); We use natural coordinates for whatwe are drawing (the world window). OpenGL converts our coordinates to screen coordinates when we set up a screen window and a viewport. The viewportmay be smaller than the screen window. The default viewportis the entire screen window. The conversion requires scaling and shifting: mapping the world window to the screen window and the viewport. Windows aredescribed by their left, top, right, and bottom values, w.l, w.t, w.r, w.b. Viewports aredescribed by the samevalues but in screen window coordinates. v.l, v.t, v.r, v.b,
- 3. glMatrixMode Specify which matrix is the current matrix C Specification void glMatrixMode( GLenum mode); Parameters Mode specifies which matrix stack is the target for subsequent matrix operations. Three values are accepted: GL_MODELVIEW, GL_PROJECTION,and GL_TEXTURE. The initial value is GL_MODELVIEW.Additionally, if the ARB_imaging extension is supported, GL_COLOR is also accepted. Description glMatrixMode sets the current matrix mode. mode can assume one of four values: GL_MODELVIEW applies subsequent matrix operations to the modelview matrix stack. GL_PROJECTION applies subsequent matrix operations to the projection matrix stack. GL_TEXTURE applies subsequent matrix operations to the texture matrix stack. GL_COLOR applies subsequent matrix operations to the color matrix stack. glRotate Multiply the current matrix by a rotation matrix C Specification void glRotated( GLdouble angle, GLdouble x, GLdouble y, GLdouble z);
- 4. void glRotatef( GLfloat angle, GLfloat x, GLfloat y, GLfloat z); Parameters Angle specifies the angle of rotation, in degrees. x, y, z specify the x, y, and z coordinates of a vector, respectively. Description glRotate produces a rotation of angle degrees around the vector x y z . The current matrix (see glMatrixMode) is multiplied by a rotation matrix with the product replacing the current matrix, as if glMultMatrix were called with the following matrix as its argument: x 2 1 - c + c x y 1 - c - z s x z 1 - c + y s 0 y x 1 - c + z s y 2 1 - c + c y z 1 - c - x s 0 x z 1 - c - y s y z 1 - c + x s z 2 1 - c + c 0 0 0 0 1 Where c = cos angle , s = sin angle , and x y z = 1 (if not, the GL will normalize this vector). If the matrix mode is either GL_MODELVIEW or GL_PROJECTION,all objects drawn after glRotate is called are rotated. Use glPushMatrix and glPopMatrix to save and restore the unrotated coordinate system. Notes This rotation follows the right-hand rule, so if the vector x y z points toward the user, the rotation will be counterclockwise. glTranslate Multiply the current matrix by a translation matrix C Specification void glTranslated(GLdouble x, GLdouble y,
- 5. GLdouble z); void glTranslatef(GLfloat x, GLfloat y, GLfloat z); Parameters x, y, z specify the x, y, and z coordinates of a translation vector. Description glTranslate produces a translation by x y z . The current matrix is multiplied by this translation matrix, with the product replacing the current matrix, as if glMultMatrixc were called with the following matrix for its argument: 1 0 0 x 0 1 0 y 0 0 1 z 0 0 0 1 If the matrix mode is either GL_MODELVIEW or GL_PROJECTION,all objects drawn after a call to glTranslate are translated. Use glPushMatrix and glPopMatrix to save and restore the untranslated coordinate system. glScale Multiply the current matrix by a general scaling matrix C Specification void glScaled(GLdouble x, GLdouble y, GLdouble z); void glScalef(GLfloat x, GLfloat y, GLfloat z); Parameters x, y, z specify scale factors along the x, y, and z axes, respectively. Description
- 6. glScale produces a non-uniform scaling along the x, y, and z axes. The three parameters indicate the desired scale factor along each of the three axes. The current matrix is multiplied by this scale matrix, and the product replaces the current matrix. If the matrix mode is either GL_MODELVIEW or GL_PROJECTION,all objects drawn after glScale is called are scaled. Use glPushMatrix and glPopMatrix to save and restore the unscaled coordinate system. Notes If scale factors other than 1 are applied to the modelview matrix and lighting is enabled, lighting often appears wrong. In that case, enable automatic normalization of normals by calling glEnable with the argument GL_NORMALIZE. glutSolidSphere,glutWireSphere glutSolidSphere and glutWireSphere render a solid or wireframe sphere respectively. Usage void glutSolidSphere(GLdouble radius, GLint slices, GLint stacks); void glutWireSphere(GLdouble radius, GLint slices, GLint stacks); Parameters Radius the radius of the sphere. Slices the number of subdivisions around the Z axis (similar to lines of longitude). Stacks the number of subdivisions along the Z axis (similar to lines of latitude). Description Renders a sphere centered at the modeling coordinates origin of the specified radius.The sphere is subdivided around the Z axis into slices and along the Z axis into stacks. glutSolidCube, glutWireCube
- 7. glutSolidCube and glutWireCube render a solid or wireframe cube respectively. Usage void glutSolidCube(GLdoublesize); void glutWireCube(GLdoublesize); Description glutSolidCube and glutWireCube render a solid or wireframe cube respectively. The cube is centered at the modeling coordinates origin with sides of length size. glutSolidCone, glutWireCone glutSolidCone and glutWireCone render a solid or wireframe cone respectively. Usage void glutSolidCone(GLdouble base, GLdouble height, GLint slices, GLint stacks); void glutWireCone(GLdouble base, GLdouble height, GLint slices, GLint stacks); Parameters Base the radius of the base of the cone. Height the height of the cone. Slices the number of subdivisions around the Z axis. Stacks the number of subdivisions along the Z axis. Description glutSolidCone and glutWireCone render a solid or wireframe cone respectively oriented along the Z axis. The base of the cone is placed at Z = 0, and the top at Z = height.The cone is subdivided around the Z axis into slices, and along the Z axis into stacks. glutSolidTorus, glutWireTorus glutSolidTorus and glutWireTorus render a solid or wireframe torus (doughnut) respectively. Usage void glutSolidTorus(GLdouble innerRadius, GLdouble outerRadius, GLint nsides, GLint rings); void glutWireTorus(GLdouble innerRadius,
- 8. GLdouble outerRadius, GLint nsides, GLint rings); InnerRadius inner radius of the torus. OuterRadius outer radius of the torus. Nsides number of sides for each radial section. Rings number of radial divisions for the torus. Description glutSolidTorus and glutWireTorus render a solid or wireframe torus (doughnut) respectively centered at the modeling coordinates origin whose axis is aligned with the Z axis. glColor3f function Sets the current color. Syntax void glColor3f( GLfloat red, GLfloat green, GLfloat blue ); Parameters Red the new red value for the current color. Green the new green value for the current color. Blue the new blue value for the current color. Returnvalue this function does not return a value. glutCreateMenu Creates a new pop-up menu. Usage int glutCreateMenu(void (*func)(int value)); Parameters Func the callback function for the menu that is called when a menu entry from the menu is selected. The value passed to the callback is determined by the value for the selected menu entry. Description
- 9. glutCreateMenu creates a new pop-up menu and returns a unique small integer identifier. The rangeof allocated identifiers starts at one. The menu identifier range is separate fromthe window identifier range. Implicitly, the currentmenu is set to the newly created menu. This menu identifier can be used when calling glutSetMenu. When the menu callback is called becausea menu entry is selected for the menu, the currentmenu willbe implicitly set to the menu with the selected entry before the callback is made.