How to get pixel coordinates between 0,1 from SV_POSITION [duplicate]

Question

I am new to HLSL and Directx. I was trying to write a simple gradient Shader by modifying one of Microsoft samples.

1.I can not understand why SV_POSITION is float4? If it is pixel coordinates shouldn't it have only x and y ? What are the 4 parts? I think SV_POSITION is not between 0,1 and the maximum val is bufferWidth,bufferHeight ... then how can I get the position between 0,1?

1. The first code does not work because distance between float2 and float4 is impossible. While the second one works I get a warning. How can I avoid the warning message because I believe something is wrong!

Fist code (Of course it should not work):

float4 VS( float4 Pos : POSITION ) : SV_POSITION
{

    return Pos;
}

float4 PS(   float4 Pos : SV_POSITION) : SV_Target
{
    float distfromcenter=distance(float2(0.5f, 0.5f), Pos);
    float4 rColor = lerp(float4(0,0,0,1),float4(1,1,1,1), saturate(distfromcenter));
    return rColor;
}

The second one :

float4 VS( float4 Pos : POSITION ) : SV_POSITION
{

    return Pos;
}


float4 PS(   float2 Pos : TEXTCOORD  ) : SV_Target
{
    float distfromcenter=distance(float2(0.5f, 0.5f), Pos);
    float4 rColor = lerp(float4(0,0,0,1),float4(1,1,1,1), saturate(distfromcenter));
    return rColor;
}

Why do I get this warning ? How can I compile this Shader using SV_POSITION to avoid the warning message ?

D3D11 ERROR: ID3D11DeviceContext::Draw: Vertex Shader - Pixel Shader linkage error: Signatures between stages are incompatible. The input stage requires Semantic/Index (TEXTCOORD,0) as input, but it is not provided by the output stage. [ EXECUTION ERROR #342: DEVICE_SHADER_LINKAGE_SEMANTICNAME_NOT_FOUND]

Answer 1

I'm new too in directx and not very good in english so i havent understand your question at all but...

Try to change the pixel shader like this:

float4 PS(float4 Pos:SV_POSITION):SV_Target //pos contain x,y,z,w but you only need x,y
{                             //remember PS is called for each pixel and so it must now the pixel-screen position
pixelPosX=Pos[0]; pixelPosY=Pos[1];//theese are the pixel coordinates in the window start from top-left corner and are integer ones(ex. 100-200, 0-0, window_width, window_height)
...
}

If the backbuffer width_height are different from window ones, i dont know if the max Pos[0] value( and Pos[1] too) is the window width or the bck buffer one.

Hope that it works.

Look the comment.

#define MAX_X 640
#define MAX_Y 400
Vertex shader....

float4 PS(float4 Pos:SV_POSITION):SV_TARGET
{
 int x=Pos[0]/MAX_X;
 .....
}