Saving a specific Camera View in OpenGL as Image - c++

Question

I have a 3D scene with an object and I would like to save a view of that object that is different from the one of the current screen I look at.
So I thought I'd just have to do something like this (pseudo code):
PushMatrix()
LoadIdentity()
TranslateAndRotate()
gluperspective()
setViewport()
DrawScene()
saveScreenshot()
PopMatrix()
But I only get a picture of the current view of my camera, not the one I specified.
Did I forget something?
EDIT:
Because of the answer below, I tried the following code:
void ScenePhotograph(GLubyte* Target, float *Translation, float RotationAroundY)
{
glMatrixMode(GL_PROJECTION);
gluPerspective(54.0f, (GLfloat)openGLControl1->Width / (GLfloat)openGLControl1->Height, 1.0f, 3000.0f);
glViewport(0,0,openGLControl1->Width, openGLControl1->Height);
glMatrixMode(GL_MODELVIEW);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(Translation[0],Translation[1],Translation[2]);
glRotatef(RotationAroundY, 0,1,0);
openGLControl1_OnDrawGL(NULL,System::EventArgs::Empty);
openGLControl1->Refresh();
glReadPixels(0, 0, openGLControl1->Width, openGLControl1->Height, GL_RGB, GL_UNSIGNED_BYTE, Target);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
cam->SetView();
openGLControl1_OnDrawGL(NULL,System::EventArgs::Empty);
openGLControl1->Refresh();
glutSwapBuffers();
}
That is giving me an access violation at glutSwapBuffers();
Any Ideas?

Answer 1

First, make sure you are not mixing diferent matrix in your code. To get a screenshot, you will need to position your camera exactly as you normally do to view it on your sccreen, but, before you swap the buffers, you read the pixels from the current framebuffer and store it as an image.
So, what you need is something like this:
glMatrixMode(GL_PROJECTION);
gluPerspective();
glMatrixMode(GL_MODELVIEW);
glClear(); // clear buffers here
loadIdendity();
setCameraPosition();
TranslateRotate();
DrawScene();
screenShot();
// do again to set your camera to correct position
glClear(); // clear buffers here
loadIdendity();
setCameraPosition();
TranslateRotate();
DrawScene();
swapBuffers();
as you can see, screenShot take care of reading the pixels from your current framebuffer and save it as an image. So do everything again to position your camera to the correct place