answer:`TexCoord` is a variable in HLSL that represents the texture coordinate of the current pixel. Each pixel on the screen corresponds to a texture coordinate, which is a 2D coordinate that maps to a specific point on the texture. In Unreal Engine 4, texture coordinates range from (0,0) at the bottom-left corner of the texture to (1,1) at the top-right corner of the texture. The `TexCoord` variable is often used in shader code to sample the texture at the current pixel. For example, `Texture.Sample(Sampler, TexCoord)` would sample the texture using the current texture coordinate at the current pixel. In the context of the scope material we discussed earlier, the `TexCoord` variable is used to calculate the distance from the current pixel to the center of the scope and to shift the texture coordinate when the pixel is inside the scope.

answer:In Unreal Engine 4, you can get the `TexCoord` variable in HLSL code by using the vertex shader output. When rendering a mesh with a material applied to it, the vertices of the mesh are processed by the vertex shader, which generates the `TexCoord` values for the mesh. These values are then interpolated across the surface of the mesh, which calculates the `TexCoord` value for each pixel in the pixel shader. Here is an example of how you can get the `TexCoord` variable in HLSL: ``` // Vertex shader input struct struct VertexInput { float3 Position : POSITION0; // Vertex position float2 TexCoord : TEXCOORD0; // Texture coordinate }; // Vertex shader output struct struct VertexOutput { float4 Position : SV_POSITION; // Output position float2 TexCoord : TEXCOORD0; // Output texture coordinate }; // Vertex shader function VertexOutput main(VertexInput Input) { VertexOutput Output; Output.Position = mul(float4(Input.Position, 1), WorldViewProjection); // Transform vertex position to clip space Output.TexCoord = Input.TexCoord; // Pass through texture coordinate return Output; } // Pixel shader function float4 main(VertexOutput Input) : SV_Target { // Access the texture coordinate using Input.TexCoord float4 Color = Texture.Sample(Sampler, Input.TexCoord); return Color; } ``` In this code, the `TexCoord` variable is defined in the `VertexInput` struct and is passed through the vertex shader to the pixel shader using the `VertexOutput` struct. The `TexCoord` variable is accessed in the pixel shader using the `Input.TexCoord` syntax. Note that this is just an example, and your vertex and pixel shader code will likely be more complex than this. But the basic idea of accessing the `TexCoord` variable from the vertex shader output should be the same.

answer:Sure, here is an HLSL code that you can use as a custom expression in Unreal Engine 4 to create the scope effect: ``` float2 ScreenCenter = float2(0.5f, 0.5f); // The center of the screen float2 ScopeCenter = float2(0.5f, 0.75f); // The center of the scope float ScopeRadius = 0.1f; // The radius of the scope float4 ScopeMaterialFunction(float2 TexCoord : TEXCOORD0) : SV_Target { float Distance = length(TexCoord - ScopeCenter); if (Distance > ScopeRadius) { return float4(0, 0, 0, 0); } else { float2 NewTexCoord = TexCoord - (ScopeCenter - ScreenCenter); return Texture.Sample(TextureSampler, NewTexCoord); } } ``` To add this code to your material, create a new Material in Unreal Engine 4, then add a new Material Expression node of type Custom. In the custom expression, paste the code above. Connect the output of the custom expression to the output node of the material. You may want to modify the constants in the code, such as `ScopeCenter` and `ScopeRadius` to fit your specific scope dimensions. You may also need to connect a texture sampler and texture node to the custom expression.

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