HLSL Textured Light: outputs only a specific part of the texture (new problem)

Question

Problem 1

I am trying to create a spotlight that instead of giving the circle within the spotlight a simple color, applies a texture to it. However, where the texture is supposed to be is only a black circle: image.

Solution: the position I used for my texture wasnt correct.

old and faulty code:

float4 TexturedSpotlightPixelShader(VertexShaderOutput input, float2 TextureCoordinate : TEXCOORD0) : COLOR0
{   
    //I left out all the other code in the shader, full code is at the bottom of the thread
    color = tex2D(SpotlightTextureSampler, TextureCoordinate); 
}

better code that solved my 'black problem (but created a new one):

float4 TexturedSpotlightPixelShader(VertexShaderOutput input) : COLOR0
{   
    //I left out all the other code in the shader, full code is at the bottom of the thread
    color = tex2D(SpotlightTextureSampler, input.Position); 
}

where at that point input.Position was set to the worldPosition in the vertexshader (which turned out was the reason for problem 2)

Problem 2

My spotlight now applies the texture, however the texture is repeated multiple times in miniature, as such: image

Solution: I added these lines in the vertex shader:

input.Position3D.w = 1.0f;
output.Position = mul(viewPosition, Projection);

and by adding/changing these lines in the pixelshader:

float2 TextureCoordinates;
TextureCoordinates.x =  input.Position.x / input.Position.w / 2.0f + 0.5f;
TextureCoordinates.y = -input.Position.y / input.Position.w / 2.0f + 0.5f;
color += tex2D(SpotlightTextureSampler, TextureCoordinates);

however, there was still a third problem.

Problem 3

The third and probably (I hope :P) the last problem, my spotlight now only shows a part of my texture and manually resizing the image (in the image file, not in my code) doesnt change what part of the texture is shown, as such: image

Solution: In my vertexshader I used the 2D positions (viewmatrix multiplied with the projection matrix) where I should have used a viewmatrix not based from my camera but from my spotlights point of view (and a projection matrix also for my spotlight's point of view)

My new code:

float4x4 View2, Projection2;

VertexShaderOutput SimpleVertexShader(VertexShaderInput input)
{
//left out a lot of code here
output.Position = mul(mul(worldPosition, View2), Projection2);
}

Full Code

Link to the shader code and the link to the xna/c# code.

Answer 1

You're using the world position as the texture coordinates. Texture coordinates range from 0 to 1 and then the texture repeats itself, so the result of this is that you'll get a copy of the texture squeezed into every 1 unit along the XY axes in world space. If your world units are centimeters then you'll get a copy of the texture in each square centimeter, for instance.

For a spotlight with a texture, you probably want projective texturing. The code in that tutorial is for D3D11, so it won't directly work in XNA, but you should be able to adapt it. The short version is that you have to transform the world position to a coordinate system aligned with the light and divide by z. This will make the texture scale larger as it gets farther from the light, like the image from a projector.