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1

I am trying to look at a cone lying on its side from above. For this I wrote the following code:

void display(void)
 
 glClear(GL_COLOR_BUFFER_BIT 

int main(int argc, char **argv)
 GLUT_DOUBLE 

I translate to the middle of the screen and then rotate 90 degrees around the x-axis, which in my idea should produce the cone on its side. The result however is a not a cone but a line which is not tilted 90 but 45 degrees. What should I change in order for the cone to show up as I want it to?

c++ opengl glut opengl-compat

share|improve this question

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

add a comment
 | 

1

I am trying to look at a cone lying on its side from above. For this I wrote the following code:

void display(void)
 
 glClear(GL_COLOR_BUFFER_BIT 

int main(int argc, char **argv)
 GLUT_DOUBLE 

I translate to the middle of the screen and then rotate 90 degrees around the x-axis, which in my idea should produce the cone on its side. The result however is a not a cone but a line which is not tilted 90 but 45 degrees. What should I change in order for the cone to show up as I want it to?

c++ opengl glut opengl-compat

share|improve this question

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

add a comment
 | 

I am trying to look at a cone lying on its side from above. For this I wrote the following code:

void display(void)
 
 glClear(GL_COLOR_BUFFER_BIT 

int main(int argc, char **argv)
 GLUT_DOUBLE 

I translate to the middle of the screen and then rotate 90 degrees around the x-axis, which in my idea should produce the cone on its side. The result however is a not a cone but a line which is not tilted 90 but 45 degrees. What should I change in order for the cone to show up as I want it to?

c++ opengl glut opengl-compat

share|improve this question

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

void display(void)
 
 glClear(GL_COLOR_BUFFER_BIT 

int main(int argc, char **argv)
 GLUT_DOUBLE 

share|improve this question

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

share|improve this question

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

edited Mar 28 at 13:37

Nicol Bolas

308k3838 gold badges516516 silver badges700700 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

asked Mar 28 at 11:21

LarsLars

3255 bronze badges

1 Answer
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2

Where is the projection matrix?

If you don't set a projection matrix, then the coordiantes have to be set in normalize device space. In NDC all the coordinates are in range [-1.0, 1.0]:

e.g.

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.5, 0.5, 0);
glRotatef(90, 1, 0, 0);
glutSolidCone(1.0, 1.0, 20, 20);
glTranslatef(-0.5, -0.5, 0);
glRotatef(-90, 1, 0, 0);

---

Alternatively you can setup an orthographic projection, which projects the world coordinates 1:1 to the window coordinates. The projection matrix can be set by glOrtho:

e.g.

void display(void)

 glClear(GL_COLOR_BUFFER_BIT 

The projection matrix describes the mapping from 3D points of the view on a scene, to 2D points on the viewport. At Orthographic Projection, the view space coordinates are linearly mapped to the clip space coordinates. The clip space coordinates are equal to the normalized device coordinates.

The normalized device coordinates are linearly mapped to the viewport rectangle.
The viewport rectangle can be defined by glViewport. Initially it is defined by the size of the window.

---

Note, that drawing by glBegin/glEnd sequences and the fixed function matrix stack is deprecated since decades. See Fixed Function Pipeline and Legacy OpenGL.
Read about Vertex Specification and Shader for a state of the art way of rendering.

share|improve this answer

edited Mar 28 at 11:39

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

add a comment
 | 

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2

Where is the projection matrix?

If you don't set a projection matrix, then the coordiantes have to be set in normalize device space. In NDC all the coordinates are in range [-1.0, 1.0]:

e.g.

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.5, 0.5, 0);
glRotatef(90, 1, 0, 0);
glutSolidCone(1.0, 1.0, 20, 20);
glTranslatef(-0.5, -0.5, 0);
glRotatef(-90, 1, 0, 0);

---

Alternatively you can setup an orthographic projection, which projects the world coordinates 1:1 to the window coordinates. The projection matrix can be set by glOrtho:

e.g.

void display(void)

 glClear(GL_COLOR_BUFFER_BIT 

The projection matrix describes the mapping from 3D points of the view on a scene, to 2D points on the viewport. At Orthographic Projection, the view space coordinates are linearly mapped to the clip space coordinates. The clip space coordinates are equal to the normalized device coordinates.

The normalized device coordinates are linearly mapped to the viewport rectangle.
The viewport rectangle can be defined by glViewport. Initially it is defined by the size of the window.

---

Note, that drawing by glBegin/glEnd sequences and the fixed function matrix stack is deprecated since decades. See Fixed Function Pipeline and Legacy OpenGL.
Read about Vertex Specification and Shader for a state of the art way of rendering.

share|improve this answer

edited Mar 28 at 11:39

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

add a comment
 | 

2

Where is the projection matrix?

If you don't set a projection matrix, then the coordiantes have to be set in normalize device space. In NDC all the coordinates are in range [-1.0, 1.0]:

e.g.

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.5, 0.5, 0);
glRotatef(90, 1, 0, 0);
glutSolidCone(1.0, 1.0, 20, 20);
glTranslatef(-0.5, -0.5, 0);
glRotatef(-90, 1, 0, 0);

---

Alternatively you can setup an orthographic projection, which projects the world coordinates 1:1 to the window coordinates. The projection matrix can be set by glOrtho:

e.g.

void display(void)

 glClear(GL_COLOR_BUFFER_BIT 

The projection matrix describes the mapping from 3D points of the view on a scene, to 2D points on the viewport. At Orthographic Projection, the view space coordinates are linearly mapped to the clip space coordinates. The clip space coordinates are equal to the normalized device coordinates.

The normalized device coordinates are linearly mapped to the viewport rectangle.
The viewport rectangle can be defined by glViewport. Initially it is defined by the size of the window.

---

Note, that drawing by glBegin/glEnd sequences and the fixed function matrix stack is deprecated since decades. See Fixed Function Pipeline and Legacy OpenGL.
Read about Vertex Specification and Shader for a state of the art way of rendering.

share|improve this answer

edited Mar 28 at 11:39

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

add a comment
 | 

Where is the projection matrix?

If you don't set a projection matrix, then the coordiantes have to be set in normalize device space. In NDC all the coordinates are in range [-1.0, 1.0]:

e.g.

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.5, 0.5, 0);
glRotatef(90, 1, 0, 0);
glutSolidCone(1.0, 1.0, 20, 20);
glTranslatef(-0.5, -0.5, 0);
glRotatef(-90, 1, 0, 0);

---

Alternatively you can setup an orthographic projection, which projects the world coordinates 1:1 to the window coordinates. The projection matrix can be set by glOrtho:

e.g.

void display(void)

 glClear(GL_COLOR_BUFFER_BIT 

The projection matrix describes the mapping from 3D points of the view on a scene, to 2D points on the viewport. At Orthographic Projection, the view space coordinates are linearly mapped to the clip space coordinates. The clip space coordinates are equal to the normalized device coordinates.

The normalized device coordinates are linearly mapped to the viewport rectangle.
The viewport rectangle can be defined by glViewport. Initially it is defined by the size of the window.

---

Note, that drawing by glBegin/glEnd sequences and the fixed function matrix stack is deprecated since decades. See Fixed Function Pipeline and Legacy OpenGL.
Read about Vertex Specification and Shader for a state of the art way of rendering.

share|improve this answer

edited Mar 28 at 11:39

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.5, 0.5, 0);
glRotatef(90, 1, 0, 0);
glutSolidCone(1.0, 1.0, 20, 20);
glTranslatef(-0.5, -0.5, 0);
glRotatef(-90, 1, 0, 0);

void display(void)

 glClear(GL_COLOR_BUFFER_BIT 

share|improve this answer

edited Mar 28 at 11:39

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges

answered Mar 28 at 11:34

Rabbid76Rabbid76

60k1313 gold badges3939 silver badges7171 bronze badges