how to get glLookAt's values once rotated - c++

so if I were to have this code
gluLookAt(0.0, 0.0, 1.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0); //Set the point looking at
glRotatef(-90, 0.0,1.0,0.0);
how can i then get each value of the new glLookAt

You probably need to go the route of using glGetDoublev to get the GL_MODELVIEW and GL_PROJECTION matrixes.

Related

Objects shake when rotating

I'm facing a problem in my opengl code
I'm trying to build a house, and rotate it 360°, for simplicity let's assume the house has the front wall with window and dor, and a back wall.
I'm using DEPTH_BUFFER not to see the back wall when viewing the front wall, and the other way around, but when I rotate the house the door and window start to shake and get distorced.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(0.0, 0.0, 0.0);
glLoadIdentity();
gluLookAt(0.0, 0.0, 40.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glRotatef(angle, 0.0, 1.0, 0.0);
glEnable(GL_DEPTH_TEST);
glColor3f(0.0, 0.0, 0.0);
glBegin(GL_POLYGON);
glVertex3f(8.0, 3.0, 0.0);
glVertex3f(8.0, -10.0, 0.0);
glVertex3f(1.0, -10.0, 0.0);
glVertex3f(1.0, 3.0, 0.0);
glEnd();
glColor3f(0.0, 0.0, 0.0);
glBegin(GL_POLYGON);
glVertex3f(-9.0, -4.0, 0.0);
glVertex3f(-9.0, 3.0, 0.0);
glVertex3f(-2.0, 3.0, 0.0);
glVertex3f(-2.0, -4.0, 0.0);
glEnd();
glColor3f(1.0, 0.0, 0.0);
glBegin(GL_POLYGON);
glVertex3f(10.0, -10.0, -20.0);
glVertex3f(-10.0, -10.0, -20.0);
glVertex3f(-10.0, 10.0, -20.0);
glVertex3f(10.0, 10.0, -20.0);
glEnd();
glColor3f(1.0, 0.0, 0.0);
glBegin(GL_POLYGON);
glVertex3f(10.0, -10.0, 0.0);
glVertex3f(10.0, 10.0, 0.0);
glVertex3f(-10.0, 10.0, 0.0);
glVertex3f(-10.0, -10.0, 0.0);
glEnd();
glDisable(GL_DEPTH_TEST);
glutSwapBuffers();
The issue is called Z-fighting. This is caused, because depth of the "door", "window" and "wall" are equal. The vertiex coordinates are transformed by the model view matrix and projection matrix and interpolated for each fragment which is covered by the polygon. This results in inaccuracies of the final z coordinate (depth).
Enable the polygon fill offset (glPolygonOffset) by before drawing the walls, to solve the issue:
glEnable(GL_DEPTH_TEST);
glDisable( GL_POLYGON_OFFSET_FILL );
// draw door and window
// ...
glEnable( GL_POLYGON_OFFSET_FILL );
glPolygonOffset( 1, 1 );
// draw walls
// ...
Polygon fill offset manipulates the depth of a fragment by a minimum amount. This causes that the depth of the "walls" is different to the depth of the "window" and "door", even after the transformation by the model view and projection matrix.
Since an offset is added to the depth of the "wall", the "wall" is always behind the window and the door, independent of the point of view.

Object Rotating in OpenGL

I'm making a square arm with push-pop matrix and pop-up menu entries. I want to make the objects rotate individually, so I create the code below but the one finger moves along with the others. Why is it moving together?
void display(void) {
glClear(GL_COLOR_BUFFER_BIT);
draw_lines();
glPushMatrix();
glColor3f(1.0, 1.0, 1.0);
glTranslatef(-1.0, 0.0, 0.0);
glRotatef((GLfloat)shoulder, 0.0, 0.0, 1.0);
glTranslatef(1.0, 0.0, 0.0);
glPushMatrix();
glScalef(2.0, 0.4, 1.5);
glutWireCube(1.0); //First square(Shoulder)
glPopMatrix();
glTranslatef(1.0, 0.0, 0.0);
glRotatef((GLfloat)elbow, 0.0, 0.0, 1.0);
glTranslatef(1.0, 0.0, 0.0);
glPushMatrix();
glScalef(2.0, 0.4, 1.5);
glutWireCube(1.0); //Second Square(Elbow)
glPopMatrix();
glTranslatef(1.0, 0.0, 0.0);
glRotatef((GLfloat)finger_1, 0.0, 0.0, 1.0);
glTranslatef(0.25, 0.0, 0.7);
glPushMatrix();
glScalef(0.5, 0.2, 0.2);
glutWireCube(1.0); //First Finger
glPopMatrix();
glTranslatef(-0.3, 0.0, 0.0);
glRotatef((GLfloat)finger_2, 0.0, 0.0, 1.0);
glTranslatef(0.25, 0.0, -0.4);
glPushMatrix();
glScalef(0.5, 0.2, 0.2);
glutWireCube(1.0); //Second Finger
glPopMatrix();
glTranslatef(-0.3, 0.0, 0.0);
glRotatef((GLfloat)finger_3, 0.0, 0.0, 1.0);
glTranslatef(0.25, 0.0, -0.5);
glPushMatrix();
glScalef(0.5, 0.2, 0.2);
glutWireCube(1.0); //Third Finger
glPopMatrix();
glPopMatrix();
glPopMatrix();
glutSwapBuffers();
}
Object rotation is made by separate functions.

Organizing the code for apartment modelling in C++ with OpenGl

I am making an apartment with C++ and openGl. I have made basic walls, roof and floor by just declaring points in the drawing function and everything of course works but code is messy and adding furniture this way would of course be very painful. So I am asking how should I organize my objects and format drawing function?
Here's the current code:
// Floor and roof of room 1
glBegin(GL_QUADS);
glNormal3f(0.0, 1.0, 0.0);
glColor3f(0.0, 1.0, 1.0);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(1.0, 0.0, 0.0);
glVertex3f(1.0, 0.0, 1.0);
glVertex3f(0.0, 0.0, 1.0);
glNormal3f(0.0, -1.0, 0.0);
glColor3f(0.0, 1.0, 0.0);
glVertex3f(0.0, 1.0, 0.0);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(1.0, 1.0, 1.0);
glVertex3f(0.0, 1.0, 1.0);
glEnd();
// Walls
glBegin(GL_QUAD_STRIP);
glNormal3f(1.0, 0.0, 0.0);
glColor3f(1.0, 1.0, 1.0);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.0, 1.0, 0.0);
glColor3f(1.0, 0.0, 0.0);
glVertex3f(0.0,0.0,1.0);
glVertex3f(0.0,1.0,1.0);
glNormal3f(0.0, 0.0, -1.0);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(1.0, 0.0, 1.0);
glVertex3f(1.0, 1.0, 1.0);
glNormal3f(-1.0, 0.0, 0.0);
glColor3f(0.5, 0.0, 0.5);
glVertex3f(1.0, 0.0, 0.0);
glVertex3f(1.0, 1.0, 0.0);
glEnd();
And so on for room 2 and door spots..
Any places to read about this subject?
You can use 3d modelling software, e.g. →Blender to define your geometry etc. Then I recommend to use →Assimp to load the exported model. Also recommend to avoid the old fixed-function pipeline – write your own little scenegraph engine and manage your matrices and 3d math with →GLM

3D texture coordinates for a cube

I want to use glTexImage3D with cube. what will be the texture coordinates for it? i am using GL_TEXTURE_3D as target.
I tried with u v coordinates same as 2d texture coordinates with z component 0-depth for each face. But that goes wrong.
These are the texture coordinates i was using which seems to be incorrect.
GLfloat texcoords[]={
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0,
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0,
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0,
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0,
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0,
0.0, 0.0,0.0,
1.0, 0.0,1.0,
1.0, 1.0,1.0,
0.0, 1.0,0.0
};
You probably do not want to use a 3D texture just for texturing the faces of a cube. More likely you want to use a cube map – essentially a set of 6 2D textures one for each face of a cube – which by its very nature nicely matches the topology of a cube.

Quaternion rotation x-axis 45 Degrees

Evening everyone,
I'm using glMultMatrixf in OpenGL to rotate my scene using the matrix:
float matrix[16] = { 1.0, 0.0, 0.0, 0.0,
0.0, 1.0, 0.0, 0.0,
0.0, 0.0, 1.0, 0.0,
0.0, 0.0, 0.0, 1.0 };
I've been following this guide (link) but its a little bit over the top for what I need.
How could I simply rotate the x-axis by 45 degrees?
Cheers
Multiplying your transformation matrix by this rotation matrix should do the trick:
float rot45X[16] = { 1.0, 0.0, 0.0, 0.0,
0.0, cos(PI/4), -sin(PI/4), 0.0,
0.0, sin(PI/4), cos(PI/4), 0.0,
0.0, 0.0, 0.0, 1.0 };
Edit: You can also of course use the utility function
glRotatef(GLfloat angle, GLfloat x, GLfloat y, GLfloat z);
where [x,y,z] indicate the axis of rotation (yes, it performs rotations around an arbitrary vector).
In your case you would need to call like this:
glRotatef(45, 1, 0, 0);