One day , I compile a OPENGL example on ubuntu9.10
“The Red Book/aargb.c”
code:
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
static float rotAngle = 0.;
/* Initialize antialiasing for RGBA mode, including alpha
- blending, hint, and line width. Print out implementation
- specific info on line width granularity and width.
*/
void init(void)
{
GLfloat values[2];
glGetFloatv (GL_LINE_WIDTH_GRANULARITY, values);
printf ("GL_LINE_WIDTH_GRANULARITY value is %3.1f
", values[0]);
glGetFloatv (GL_LINE_WIDTH_RANGE, values);
printf ("GL_LINE_WIDTH_RANGE values are %3.1f %3.1f
",
values[0], values[1]);
glEnable (GL_LINE_SMOOTH);
glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glHint (GL_LINE_SMOOTH_HINT, GL_DONT_CARE);
glLineWidth (1.5);
glClearColor(0.0, 0.0, 0.0, 0.0);
}
/* Draw 2 diagonal lines to form an X
*/
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f (0.0, 1.0, 0.0);
glPushMatrix();
glRotatef(-rotAngle, 0.0, 0.0, 0.1);
glBegin (GL_LINES);
glVertex2f (-0.5, 0.5);
glVertex2f (0.5, -0.5);
glEnd ();
glPopMatrix();
glColor3f (0.0, 0.0, 1.0);
glPushMatrix();
glRotatef(rotAngle, 0.0, 0.0, 0.1);
glBegin (GL_LINES);
glVertex2f (0.5, 0.5);
glVertex2f (-0.5, -0.5);
glEnd ();
glPopMatrix();
glFlush();
}
void reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if (w <= h)
gluOrtho2D (-1.0, 1.0,
-1.0*(GLfloat)h/(GLfloat)w, 1.0*(GLfloat)h/(GLfloat)w);
else
gluOrtho2D (-1.0*(GLfloat)w/(GLfloat)h,
1.0*(GLfloat)w/(GLfloat)h, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case ‘r’:
case ‘R’:
rotAngle += 20.;
if (rotAngle >= 360.) rotAngle = 0.;
glutPostRedisplay();
break;
case 27: /* Escape Key */
exit(0);
break;
default:
break;
}
}
/* Main Loop
- Open window with initial window size, title bar,
- RGBA display mode, and handle input events.
/
int main(int argc, char* argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (200, 200);
glutCreateWindow (argv[0]);
init();
glutReshapeFunc (reshape);
glutKeyboardFunc (keyboard);
glutDisplayFunc (display);
glutMainLoop();
return 0;
}
And I use this command: gcc -o test -lglut aargb.c
then run ./test
I got a FullScreen, And is black.
Then I test other opengl example, if who use “GLUT_DOUBLE” Display Mode, they will display correctly.
What is the reason？
