After a lot of struggle with UnProject, I switched to glOrtho. It seems to work great for what I need, except zooming in and out. This was trivial with gluPerspective. :(


My problem is when I zoom out, it's as if the vanishing point in gluPerspective were the top left corner of the window. Everything shrinks into that corner when I really just want to zoom out and have objects stay in their place on the screen. What do I have to do to accomplish this?

Here's my function to change the glOrtho arguments

void GameplayState::SetProjection(){        GLint viewport[4];                     glGetIntegerv(GL_VIEWPORT, viewport);        int zoomedWidth = viewport[2] / (2.0f*this->zoomFactor);        int zoomedHeight = viewport[3] / (2.0f*this->zoomFactor);        glOrtho(0, zoomedWidth, zoomedHeight, 0, 0, 1);        glMatrixMode(GL_MODELVIEW);        glLoadIdentity();}

You can either translate the objects to the new position or, ironically, make glOrtho work with the origin being at the center of the screen. Something like glOrtho(-zoomedWidth/2, zoomedWidth/2, zoomedHeight/2, -zoomedHeight/2, 0, 1); should do the trick.

Quote:Original post by kibokun
After a lot of struggle with UnProject, I switched to glOrtho. It seems to work great for what I need, except zooming in and out. This was trivial with gluPerspective. :(


My problem is when I zoom out, it's as if the vanishing point in gluPerspective were the top left corner of the window. Everything shrinks into that corner when I really just want to zoom out and have objects stay in their place on the screen. What do I have to do to accomplish this?

Here's my function to change the glOrtho arguments

void GameplayState::SetProjection(){        GLint viewport[4];                     glGetIntegerv(GL_VIEWPORT, viewport);        int zoomedWidth = viewport[2] / (2.0f*this->zoomFactor);        int zoomedHeight = viewport[3] / (2.0f*this->zoomFactor);        glOrtho(0, zoomedWidth, zoomedHeight, 0, 0, 1);        glMatrixMode(GL_MODELVIEW);        glLoadIdentity();}

glOrtho() taks the left, right, bottom, and top bounds of the visible region as arguments. In your case, the view remains achored at a corner because you always make the top-left corner (0, 0). If you don't want the view to be anchored at the top-left corner, then don't achor the view at the top-left corner :)

It might help to think of your orthographic projection in terms of a center (focal) point, an aspect ratio, and a zoom value. Here's an example of how you might derive the glOrtho() arguments from these values:

float yExtent = zoom;float xExtent = yExtent * aspectRatio;float left = center.x - xExtent;float right = center.x + xExtent;// You can swap these if you want +y to go from top to bottom:float bottom = center.y - yExtent;float top = center.y + yExtent;

You can then move your virtual camera around by modifying its 'center' value, and zoom in and out by modifying the 'zoom' value.