Getting Started with Direct3D - Learning Windows 8 Game Development - page 20

Down the graphics pipeline
Let's step aside for a moment to understand the stages that the graphics card goes
through when it renders something to the screen, also called the graphics pipeline .
To do this, we need to understand what exactly is drawn to the screen, even when
we're just working in 2D. The base component of something drawn onto the screen is
a vertex . The vertex is a point in space, that, when combined with at least two other
points, forms a solid triangle that can be rendered. By combining multiple triangles
together, you can create anything from a simple square to a detailed 3D model with
thousands of triangles.
Often, vertices will share the same space, so we need a way to reduce the repetition
and memory use by only defining a vertex once. However, how do we indicate which
triangles use this vertex? This is where the index enters. Just as with arrays, the in-
dex allows you to map to a particular vertex using much less memory. This way you
can have a lot of data per vertex, and reference a single vertex multiple times by de-
fining the triangles with an array of indices.
How does all this get mapped and calculated so that we render the right thing? This is
where the Input Assembler ( IA ) comes into play. The IA takes the vertex and index
buffers (arrays) and builds a list of triangle vertices that need to be drawn. These are
then passed to the vertex shader .
The vertex shader is a piece of code that we use to map the 3D position of a vertex
to its 2D position on the screen. We'll be using DirectXTK for this so we can avoid
worrying about vertex shaders for now; however if you want to start adding awesome
visual features and take advantage of the hardware, you will want to learn about these
shaders. Vertex shaders are written in a language called the High Level Shader Lan-
guage ( HLSL ).
Once we have a transformed vertex, we can take advantage of some new Direct3D
10.0 and Direct3D 11.0 features: the tessellation shader and the geometry shader .
Tessellation refers to the act of increasing geometric detail by adding more triangles.
This is done through two different shaders, the hull shader and the domain shader .
Tessellation is an advanced topic that is too big for this topic. I encourage you to take
a look at the many resources available online if you're interested in this topic.