I'm trying to get the mouse click position on a terrain geometry, but multiple times in each frame; doing it on the CPU was way too slow, so I'm trying to do it with a compute shader. I can't seem to get a valid result back. I guess it's somehow related to my raydirection/rayorigin vectors, because I tried 4 different written DirectX HLSL solutions, but none of them works for my case; though, I did have to modify them. Anyway, this is my code to generate the ray vectors:
XMFLOAT3 RayOriginFloat = m_Camera->GetPosition(); //The eye position of the camera. I use this vector in the compute shader. XMVECTOR worldPos; XMVECTOR RayOrigin = XMLoadFloat3(&RayOriginFloat); DirectX::BoundingFrustum frustum; // I use the DirectXMath XMVector3Unproject method to project the mouse coord to worldspace. ScreenToWorld(m_mouseX, m_mouseY, &worldPos); XMVECTOR RayDir = worldPos - RayOrigin; RayDir = XMVector3Normalize(RayDir); //And finally the normalized direction vector And this is the HLSL code:
cbuffer RayBuffer { float3 RayOrigin; float3 RayDir; matrix view; }; struct ComputeInputType { float3 position : POSITION; float2 tex : TEXCOORD; float3 normal : NORMAL; }; struct ComputeOutputType { float distance; float3 position; }; static const uint ThreadSize = 32; StructuredBuffer<ComputeInputType> BufferIn : register(t0); RWStructuredBuffer<ComputeOutputType> BufferOut : register(u0); [numthreads(ThreadSize, ThreadSize, 1)] void PickingCSMain(uint3 dispatchThreadID : SV_DispatchThreadID) { float result; float3 vertices[3]; float3 edge[2]; if (dispatchThreadID.x < 64 && dispatchThreadID.y < 64) { vertices[0] = BufferIn[(dispatchThreadID.x + dispatchThreadID.y * ThreadSize * 2)].position; vertices[1] = BufferIn[(dispatchThreadID.x + (dispatchThreadID.y + 1) * ThreadSize * 2)].position; vertices[2] = BufferIn[(dispatchThreadID.x + 1 + (dispatchThreadID.y + 1) * ThreadSize * 2)].position; edge[0] = vertices[1].xyz - vertices[0].xyz; edge[1] = vertices[2].xyz - vertices[0].xyz; float3 normal = normalize(cross(edge[0], edge[1])); float b = dot(normal, RayDir); float3 w0 = RayOrigin - vertices[0].xyz; float a = -dot(normal, w0); float t = a / b; result = t; float3 p = RayOrigin + t * RayDir; float uu, uv, vv, wu, wv, inverseD; uu = dot(edge[0], edge[0]); uv = dot(edge[0], edge[1]); vv = dot(edge[1], edge[1]); float3 w = p - vertices[0].xyz; wu = dot(w, edge[0]); wv = dot(w, edge[1]); inverseD = uv * uv - uu * vv; inverseD = 1.0f / inverseD; float u = (uv * wv - vv * wu) * inverseD; if (u < 0.0f || u > 1.0f) { result = -1.0f; } float v = (uv * wu - uu * wv) * inverseD; if (v < 0.0f || (u + v) > 1.0f) { result = -1.0f; } BufferOut[(dispatchThreadID.x + dispatchThreadID.y * ThreadSize * 2)].distance = result; BufferOut[(dispatchThreadID.x + dispatchThreadID.y * ThreadSize * 2)].position = vertices[0].xyz; } } The result is always -1.0f. I don't get it; I might have made a big mistake, but I can't find where.
Why does my triangle ray intersection test always return -1.0f?
