Perspective Projections
Using Perspective Projections
To see your objects, you need to make sure they are in the frustum.
gluPerspective( 45.0, 1.0, 3.0, 7.0 ); ... /* sometime before drawing scene */ glTranslatef( 0, 0, -5.0 );
1: /* matrixmodes.c - draw a triangle under the effect of a rotation,
2: * a translation and a scale; use the matrix stack
3: * to ensure that the scene is properly redrawn.
4: *
5: * Escape Key - exit program
6: */
7:
8: #include <GL/glut.h> /* includes gl.h, glu.h */
9:
10: #include <stdio.h>
11:
12: #include "axes.h"
13:
14: /* Function Prototypes */
15:
16: GLvoid initgfx( GLvoid );
17: GLvoid keyboard( GLubyte, GLint, GLint );
18: GLvoid drawScene( GLvoid );
19:
20: void drawTriangle( GLfloat red, GLfloat green, GLfloat blue );
21:
22: void printHelp( char * );
23:
24: /* Global Definitions */
25:
26: #define KEY_ESC 27 /* ascii value for the escape key */
27:
28: void
29: main( int argc, char *argv[] )
30: {
31: GLsizei width, height;
32:
33: glutInit( &argc, argv );
34:
35: width = glutGet( GLUT_SCREEN_WIDTH );
36: height = glutGet( GLUT_SCREEN_HEIGHT );
37: glutInitWindowPosition( (width / 2) + 2, height / 4 );
38: glutInitWindowSize( width / 2, height / 2 );
39: glutInitDisplayMode( GLUT_RGBA );
40: glutCreateWindow( argv[0] );
41:
42: initgfx();
43:
44: glutKeyboardFunc( keyboard );
45: glutDisplayFunc( drawScene );
46:
47: printHelp( argv[0] );
48:
49: glMatrixMode( GL_PROJECTION );
50: gluPerspective( 45.0, (GLdouble) width/ (GLdouble)height, 3.0, 7.0 );
51: glMatrixMode( GL_MODELVIEW );
52:
53: glutMainLoop();
54: }
55:
56: void
57: printHelp( char *progname )
58: {
59: fprintf(stdout,
60: "\n%s - demonstrates use of matrix modes and stacks\n\n"
61: "Escape Key - exit the program\n\n",
62: progname);
63: }
64:
65: GLvoid
66: initgfx( GLvoid )
67: {
68: glClearColor( 0.0, 0.0, 1.0, 1.0 );
69: glShadeModel( GL_FLAT );
70: }
71:
72: GLvoid
73: keyboard( GLubyte key, GLint x, GLint y )
74: {
75: switch (key) {
76: case KEY_ESC: /* Exit whenever the Escape key is pressed */
77: exit(0);
78: }
79: }
80:
81: GLvoid
82: drawTriangle( GLfloat red, GLfloat green, GLfloat blue )
83: {
84: glColor3f( red, green, blue );
85: glBegin( GL_TRIANGLES );
86: glVertex2f( -0.5, -0.5 );
87: glVertex2f( 0.5, -0.5 );
88: glVertex2f( 0.0, 0.5 );
89: glEnd();
90: }
91:
92: GLvoid
93: drawScene( GLvoid )
94: {
95: glClear( GL_COLOR_BUFFER_BIT );
96:
97: glPushMatrix();
98: /* Translate the origin so that it is between the near and far
99: * clipping planes.
100: */
101: glTranslatef( 0.0, 0.0, -5.0 );
102:
103: /* draw a black triangle centered at the origin */
104: drawTriangle( 0.0, 0.0, 0.0 );
105:
106: /* Draw x and y axes to show the origin */
107: XYaxes();
108:
109: /* move over a bit and draw another triangle */
110: glTranslatef( 0.5, 0.0, 0.0 );
111: drawTriangle( 0.3, 0.3, 0.3 );
112:
113: /* move over a bit and draw a rotated triangle */
114: glTranslatef( 0.5, 0.0, 0.0 );
115:
116: /* Rotate 15 degrees counter-clockwise around the positive Z axis */
117: glRotatef( -15.0, 0.0, 0.0, 1.0 );
118: drawTriangle( 0.7, 0.7, 0.7 );
119:
120: /* move over a bit and draw a scaled triangle */
121: glTranslatef( 0.5, 0.0, 0.0 );
122:
123: /* Scale the triangle by one-half in all dimensions */
124: glScalef( -0.5, 0.5, 0.5 );
125: drawTriangle( 1.0, 1.0, 1.0 ); /* draw green triangle */
126: XYaxes();
127:
128: glPopMatrix();
129:
130: glFlush();
131: }