let's say I have world coordinates stored in a variable Position and I want to calculate
the Normalized Device Coordinates (NDC) for this Position on the CPU in C++ code.
Using a ModelViewProjectionMatrix which contains a perspective projection matrix I would do it like this:
Code :// Calculate clip space position s_Position= ModelViewProjectionMatrix * glm::vec4(Position, Position, Position, 1.0f); // Transform from clip space to normalized device coordiantes by doing the "perspective divide" [-1,1] // See here: [URL]http://www.songho.ca/opengl/gl_transform.html[/URL] s_Position.x= s_Position.x / s_Position.w; s_Position.y= s_Position.y / s_Position.w; s_Position.z= s_Position.z / s_Position.w; // Calculate window depth coordinate which would be the value written to the depth buffer [0,1] s_Position.z= s_Position.z * 0.5f + 0.5f;
This should give me s_Position's x and y in a range [-1,1] and z in a range [0,1].
I hope that is correct so far.
Now I want to achieve the same thing but with a ModelViewProjectionMatrix which contains
an orthographic projection matrix.
But in this case w is always 1 so there is no "perpsective-divide".
So which step is performed between vertex and fragment shader to
get the NDC and how can I achieve the same result on CPU side?
Help is really appreciated!