DirectX11 texture coordinates and vertices

Question

I am new to StackOverflow.

I am studying DirectX11 from the book Beginning Directx11 and I am a complete beginner but I do have knowledge of C++. I have come across texture coordinates and how they are used but I don't understand the snippet of code that is used to specify the vertices. Below is the code:

// the structure used to store the vertices
struct VertexPos
{
    XMFLOAT3 pos;
    XMFLOAT2 tex0;
};

// some code before reaching this point
...
VertexPos vertices[] =
{
    { XMFLOAT3(  1.0f,  1.0f, 1.0f ), XMFLOAT2( 1.0f, 1.0f ) },
    { XMFLOAT3(  1.0f, -1.0f, 1.0f ), XMFLOAT2( 1.0f, 0.0f ) },
    { XMFLOAT3( -1.0f, -1.0f, 1.0f ), XMFLOAT2( 0.0f, 0.0f ) },

    { XMFLOAT3( -1.0f, -1.0f, 1.0f ), XMFLOAT2( 0.0f, 0.0f ) },
    { XMFLOAT3( -1.0f,  1.0f, 1.0f ), XMFLOAT2( 0.0f, 1.0f ) },
    { XMFLOAT3(  1.0f,  1.0f, 1.0f ), XMFLOAT2( 1.0f, 1.0f ) },
};
...

// shader file
Texture2D colorMap_ : register( t0 );
SamplerState colorSampler_ : register( s0 );


struct VS_Input
{
    float4 pos  : POSITION;
    float2 tex0 : TEXCOORD0;
};

struct PS_Input
{
    float4 pos  : SV_POSITION;
    float2 tex0 : TEXCOORD0;
};


PS_Input VS_Main( VS_Input vertex )
{
    PS_Input vsOut = ( PS_Input )0;
    vsOut.pos = vertex.pos;
    vsOut.tex0 = vertex.tex0;

    return vsOut;
}

I don't understand why there are 6 positions specified. If it is to make a rectangle, is it not possible to specify 4 values and make a rectangle from two triangles? This loads a texture image and displays it, I would like to know how the vertices work (if possible with a drawing specifying the position of each vertex).

Answer 1

I would say this example uses real triangles (each triangle 3 vertices together 6), if you want 4 vertices and two triangles you can use Triangle Strip https://en.wikipedia.org/wiki/Triangle_strip