How to handle the orthographic projection when auto-rotating screen? - objective-c

Question

I have this method for performing the ortho projection:
void myGL::ApplyOrtho(float maxX, float maxY) const
{
float a = 1.0f / maxX;
float b = 1.0f / maxY;
float ortho[16] = {
a, 0, 0, 0,
0, b, 0, 0,
0, 0, -1, 0,
0, 0, 0, 1};
GLint projectionUniform = glGetUniformLocation(m_simpleProgram, "Projection");
glUniformMatrix4fv(projectionUniform, 1, 0, &ortho[0]);
}
It works fine for iPad screen when I do this:
ApplyOrtho(2, 2*1024/768);
Here's my rendered image:
However, when I rotate to landscape, it looks like this:
Now my assumption is this is because the ApplyOrtho matrix is setting a fixed projection and that projection does not rotate while the image is rotating within that projection, thus getting displayed fatter.
Incidentally, this is the rotation:
void myGL::ApplyRotation(float degrees) const
{
float radians = degrees * 3.14159f / 180.0f;
float s = std::sin(radians);
float c = std::cos(radians);
float zRotation[16] = {
c, s, 0, 0,
-s, c, 0, 0,
0, 0, 1, 0,
0, 0, 0, 1
};
GLint modelviewUniform = glGetUniformLocation(m_simpleProgram, "Modelview");
glUniformMatrix4fv(modelviewUniform, 1, 0, &zRotation[0]);
}
It is used right before drawing.
So I experimented and tried this at the same time I rotate:
ApplyOrtho(2*1024/768, 2);
However this has no effect whatsoever, even though the rotation is definitely happening at the same time. My image remains "fat".
Is my interpretation of why the fatness is happening correct?
How to handle the orthographic projection when auto-rotating screen?
UDPATE: Also tried this on iPhone using the 2/3 dimensions of the screen (not iPhone 5) and using ApplyOrtho(2,3) and ApplyOrtho(3,2) but the "fat" triangle in landscape remains.
Also: the viewport is setup just once, before the first Ortho:
glViewport(0, 0, width, height);
Where width and height are the dimensions of the Portrait screen.

Answer 1

The cause of the above discrepancies is that the orthographic projection is not matching the width and height ratio of the screen, thus the X and Y coordinates are not the same screen size. Making the orthographic ratio match the viewport ratio resolves this issue. As a result, when rotating, the image will remain exactly the same shape and size.