Mar 10
25

10. OpenGL Scaling

9 Comments



If you have worked with vectors before, you will know already that
scaling is simply stretching an object a certain amount.

Say we have an object, but we want it twice the height, we will
have to scale (stretch) it to twice the current height, along the y axis.

I am using:
glScalef(2, 0.5, 1);
in my display function.

If you look at the scale function on its own it takes:
The amount you want to stretch it on the:
x axis
y axis
z axis
In that order.

So I am stretching my cube, 2 times along the x axis, 0.5 times along the
y axis, and 1 time on the z axis.

So it will come out, twice as long, half as high, and the same depth.

And that is all there is to scaling, it is one of the very basic commands
in OpenGL.

If there are any problems with this code, please email me at swiftless@gmail.com

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59. 		    #include <GL/gl.h>
#include <GL/glut.h>

GLfloat angle = 0.0;

void cube (void) {
    //scaled
    glScalef( 2.0, 0.5, 1.0 );  //twice as wide, half the height, 
same depth
    glRotatef(angle, 1.0, 0.0, 0.0);
    glRotatef(angle, 0.0, 1.0, 0.0);
    glRotatef(angle, 0.0, 0.0, 1.0);
    glColor4f(1.0, 0.0, 0.0, 0.25); //25% visible
    glutWireCube(2);
    //non scaled
    glRotatef(angle, 1.0, 0.0, 0.0);
    glRotatef(angle, 0.0, 1.0, 0.0);
    glRotatef(angle, 0.0, 0.0, 1.0);
    glColor4f(0.0, 1.0, 0.0, 0.25); //25% visible
    glutSolidCube(1);
}

void display (void) {
    glClearColor (0.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT);
    glEnable(GL_BLEND); //enable the blending
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); /
/ set the blending
    glLoadIdentity();  
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    cube();
    glutSwapBuffers();
    angle ++;
}

void reshape (int w, int h) {
    glViewport (0, 0, (GLsizei)w, (GLsizei)h);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0)
;
    glMatrixMode (GL_MODELVIEW);
}

int main (int argc, char **argv) {
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA); //set up 
for the alpha channel
    glutInitWindowSize (500, 500);
    glutInitWindowPosition (100, 100);
    glutCreateWindow (“A basic OpenGL Window“);
    glutDisplayFunc (display);
    glutIdleFunc (display);
    glutReshapeFunc (reshape);
    glutMainLoop ();
    return 0;
}

Related posts:

  1. 8. OpenGL Double Buffering
  2. 7. OpenGL Rotation and Translation (Version 2.0)
  3. 30. OpenGL Circle Drawing
  4. 9. OpenGL Blending
  5. 6. OpenGL Cube (Version 2.0)

Tags: , , , , ,


This entry was posted on March 25, 2010 at 5:47 am. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Posted in OpenGL by Swiftless 9 Comments

9 Responses to "10. OpenGL Scaling"

  • kropcke says:
    November 11, 2011 at 3:32 pm
    Reply

    Thank you again very much Swiftless.

    I’m getting a little more time nowadays to go through your tutorials. And I just want to say that I deeply appreciate all your hard work and for sharing your expertise and thoughts with the rest of us.

    I don’t think any of us take your time lightly. It is very kind of you.

    -kropcke

  • andrew says:
    June 5, 2011 at 5:16 am
    Reply

    For some reason The section of code you give is almost completely pushed out of the frame. I noticed this only seems to happen on pages where the ads are actually next to the section of code. I’m not sure if it’s a CSS issue or what but it does make it a little hard to read on some pages. The only browsers I have noticed this on have been Chrome and Explorer, I don’t use firefox anymore so I don’t know if it’s there too.

    • Swiftless says:
      June 5, 2011 at 11:42 am
      Reply

      Hi Andrew,

      This is a known problem. It occurred when I transferred the site from manual php to WordPress. The version 2 and newest tutorials don’t suffer from it because they are WordPress friendly. It’s one of those things I still have to get around to fixing.

      Thanks,
      Swiftless

  • a man says:
    May 15, 2011 at 2:13 am
    Reply

    i cant see anything getting changed

  • Imrn says:
    July 27, 2010 at 5:06 am
    Reply

    the scale functions seems to be applying on both cubes, I tried adding glScalef( 1.0, 1.0, 1.0) before the rotation lines of second cube but both cubes get scaled

    • Swiftless says:
      July 27, 2010 at 9:40 am
      Reply

      Hi Imrn,

      Yes, anything you do will be applied to all the following shapes unless you use glPushMatrix and glPopMatrix, which are mentioned in a later tutorial.

      Cheers,
      Swiftless

  • Swiftless says:
    April 6, 2010 at 11:48 am
    Reply

    Thanks for the feedback.

    I have noticed some issues with the code, this is all fixed in the new versions of the tutorials, once I get around to writing them all that is.

    Cheers,
    Swiftless

  • pennypacker says:
    April 6, 2010 at 11:43 am
    Reply

    Great tutorial! Like the page’s design too :)

    A minor gripe though: Some of the comments are split up by line breaks. You should use /**/ comments instead.

Leave a Comment

Improve the web with Nofollow Reciprocity.