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Block Engine -->
The point if this section is to argue that
based on some of the current limitations of OpenGL,
the best way to render a block world is with a shader.
That is, there are several limitations that together
from a perfect storm of not being able to render
block worlds efficiently without using a shader.
Limitation 1: No Texture Wrapping in a Texture Atlas
A texture atlas a very useful because it allows us
to have all our block textures be subrectangles of one big
Once we have created this texture atlas,
there is no need to swap textures when rendering.
When using a texture atlas, the texture coordinates
we use for our verticies will be within the subrectangle
that corresponds to the block texture we want.
Texture wrapping refers to when a texture coordinate
t (which is a float) is converted to a float
between 0.0 and 1.0 (by wrapping).
There are various situations in which we would like to
use texture wrapping.
Suppose that we are using a texture atlas and
we also want to use texture wrapping.
Let's say the block texture we want to use is occupying
the subrectanble (min_u,
of our texture atlas.
Given a texture coordinate pair (u,v), one
would think there would be a way to tell OpenGL
to wrap the coordinates inside the subrectanble
(so that u is between min_u and
v is between min_v and max_v).
However, this feature seems to be missing from
the current version of OpenGL.
If we want to accomplish this,
we must use a shader.
Limitation 2: Tex Coords Bound to Verticies in VBOs
It would be ideal if we could use three buffers:
A buffer of
A buffer of
A buffer of indicies
into the vertex and texture coordinate
The elements of the third buffer,
the index buffer would
come in groups of 3 to describe
Unfortunately, OpenGL does not allow us to
To my knowledge, OpenGL only allows
our index buffer to contain indicies
for a single buffer.
Furthermore, each tripple of vertex coordinates
has to be right next to a pair of
This is unfortunate, because each vertex
of our block world will have multiple
texture coordinates associated with it,
forcing us to duplicate vertex information.
Because of these two limitations, it
appears as through we cannot render block
worlds in OpenGL anywhere close to optimally
without writing a shader to handle texture