Question

I have installed GLUT and Visual Studio 2010 and found some tutorials on OpenGL basics (www.opengl-tutorial.org) and 2D graphics programming. I have advanced knowledge in C but no expirience with graphics programming…

For project (astronomy – time scales) , i must create one object in center of window and make other 5 objects (circles,dots…) to rotate around centered object with respect to some equations (i can implement them and solve). Equations is for calculating coordinates of that 5 objects and all of equations have parameter t (as time). For creating animation i will vary parameter t from 0 to 2pi with some step and get coordinates in different moments. If task was to print new coordinates of objects it would be easy to me but problem is how to make animation of graphics. Can i use some functions of OpenGL for rotation/translation ? How to make an object to move to desired location with coordinates determined by equation? Or i can redraw object in new coordinates every millisecond? First thing i thought was to draw all objects, calculate new coordinates, clear screen and draw all objects in new coordinates and repeat that infinitely..(it would be primitive but will work?)

Here is screen shot of that objects – http://i.snag.gy/ht7tG.jpg . My question is how to make animation by calculating new coordinates of objects each step and moving them to new location. Can i do that with basics in OpenGL and good knowledge of C and geometry? Any ideas from what to start? Thanks

Answer 1

Or i can redraw object in new coordinates every millisecond? First
thing i thought was to draw all objects, calculate new coordinates,
clear screen and draw all objects in new coordinates and repeat that
infinitely..

This is indeed the way to go. I would further suggest that you don’t bother with shaders and vertex buffers as is the OpenGL 3/4 way. What would be easiest is called “immediate mode”, deprecated by OpenGL 3/4 but available in 1/2/3. It’s easy:

glPushMatrix(); //save modelview matrix
  glTranslatef(obj->x, obj->y, obj->z); //move origin to object center
  glBegin(GL_TRIANGLES); //start drawing triangles
    glColor3f(1.0f, 0.0f, 0.0f); //a nice red one
    glVertex3f(0.0, +0.6f, 0.0f);
    glVertex3f(-0.4f, 0.0f, 0.0f);
    glVertex3f(+0.4f, 0.0f, 0.0f); //almost equilateral
  glEnd();
glPopMatrix(); //restore modelview matrix/origin

Do look into helper libraries glu (useful for setting up the camera / the projection matrix) and glut (should make it very easy to set up a window and basic controls and drawing).

It would probably take you longer to set it up (display a rotating triangle) than to figure out how to use it. In fact, here’s some code to help you get started. Your first challenge could be to set up a 2D orthogonal projection matrix that projects along the Z-axis, so you can use the 2D functions (glVertex2).