What are the coordinates of the vertices in OpenGL?
OpenGL expects all the vertices, that we want to become visible, to be in normalized device coordinates after each vertex shader run. That is, the x, y and z coordinates of each vertex should be between -1.0 and 1.0; coordinates outside this range will not be visible.
How is the signed area calculated in OpenGL?
OpenGL face culling calculates the signed area of the filled primitive in window coordinate space. The signed area is positive when the window coordinates are in a counter-clockwise order and negative when clockwise.
When do you apply perspective division in OpenGL?
OpenGL requires that the visible coordinates fall between the range -1.0 and 1.0 as the final vertex shader output, thus once the coordinates are in clip space, perspective division is applied to the clip space coordinates: o u t = (x / w y / w z / w)
Why does the OpenGL globe appear to be solid?
The globe appears to be nearly solid because it’s composed of hundreds of colored blocks, and you see the wireframe lines for all the edges of all the blocks, even those forming the back side of the globe. The way the globe is constructed gives you an idea of how complex objects can be created by assembling lower-level objects.
When does OpenGL clip coordinates close to the camera?
Whenever the near value of your perspective matrix is set too high (like 10.0), OpenGL will clip all coordinates close to the camera (between 0.0 and 10.0), which can give a visual result you maybe have seen before in videogames where you could see through certain objects when moving uncomfortably close to them.
How to transform vertex coordinates from view to clip-space?
To transform vertex coordinates from view to clip-space we define a so called projection matrix that specifies a range of coordinates e.g. -1000 and 1000 in each dimension. The projection matrix then transforms coordinates within this specified range to normalized device coordinates (-1.0, 1.0).