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////////////////////////////////////////////////////////////////////////////////
//   0 1 2 3 4 5 6 7
// 0 + . . . . . . .
// 1 . . . . . . . .
// 2 . . . . . . . .
// 3 . . . * . . . .
// 4 . . . . . . . .
// 5 . . . . . . . .
// 6 . . . . . . . .
// 7 . . . . . . . .
//
// * - Base point for every thread, + - pixel around which ColorDistance is
// computed
// The idea behind this method:
// - Every thread in a 8x8 block computes just one ColorDistance
// - It is saved in the weights array that is shared across the threads
// - Threads are synced
// - For every pixel inside the block weights are considered to be constants
////////////////////////////////////////////////////////////////////////////////
#include <cooperative_groups.h>

namespace cg = cooperative_groups;

__global__ void NLM2(TColor *dst, int imageW, int imageH, float Noise, float lerpC, cudaTextureObject_t texImage)
{
    // Handle to thread block group
    cg::thread_block cta = cg::this_thread_block();

    // Weights cache
    __shared__ float fWeights[BLOCKDIM_X * BLOCKDIM_Y];

    const int ix = blockDim.x * blockIdx.x + threadIdx.x;
    const int iy = blockDim.y * blockIdx.y + threadIdx.y;
    // Add half of a texel to always address exact texel centers
    const float x  = (float)ix + 0.5f;
    const float y  = (float)iy + 0.5f;
    const float cx = blockDim.x * blockIdx.x + NLM_WINDOW_RADIUS + 0.5f;
    const float cy = blockDim.x * blockIdx.y + NLM_WINDOW_RADIUS + 0.5f;

    if (ix < imageW && iy < imageH) {
        // Find color distance from current texel to the center of NLM window
        float weight = 0;

        for (float n = -NLM_BLOCK_RADIUS; n <= NLM_BLOCK_RADIUS; n++)
            for (float m = -NLM_BLOCK_RADIUS; m <= NLM_BLOCK_RADIUS; m++)
                weight += vecLen(tex2D<float4>(texImage, cx + m, cy + n), tex2D<float4>(texImage, x + m, y + n));

        // Geometric distance from current texel to the center of NLM window
        float dist = (threadIdx.x - NLM_WINDOW_RADIUS) * (threadIdx.x - NLM_WINDOW_RADIUS)
                   + (threadIdx.y - NLM_WINDOW_RADIUS) * (threadIdx.y - NLM_WINDOW_RADIUS);

        // Derive final weight from color and geometric distance
        weight = __expf(-(weight * Noise + dist * INV_NLM_WINDOW_AREA));

        // Write the result to shared memory
        fWeights[threadIdx.y * BLOCKDIM_X + threadIdx.x] = weight;
        // Wait until all the weights are ready
        cg::sync(cta);

        // Normalized counter for the NLM weight threshold
        float fCount = 0;
        // Total sum of pixel weights
        float sumWeights = 0;
        // Result accumulator
        float3 clr = {0, 0, 0};

        int idx = 0;

        // Cycle through NLM window, surrounding (x, y) texel
        for (float i = -NLM_WINDOW_RADIUS; i <= NLM_WINDOW_RADIUS + 1; i++)
            for (float j = -NLM_WINDOW_RADIUS; j <= NLM_WINDOW_RADIUS + 1; j++) {
                // Load precomputed weight
                float weightIJ = fWeights[idx++];

                // Accumulate (x + j, y + i) texel color with computed weight
                float4 clrIJ = tex2D<float4>(texImage, x + j, y + i);
                clr.x += clrIJ.x * weightIJ;
                clr.y += clrIJ.y * weightIJ;
                clr.z += clrIJ.z * weightIJ;

                // Sum of weights for color normalization to [0..1] range
                sumWeights += weightIJ;

                // Update weight counter, if NLM weight for current window texel
                // exceeds the weight threshold
                fCount += (weightIJ > NLM_WEIGHT_THRESHOLD) ? INV_NLM_WINDOW_AREA : 0;
            }

        // Normalize result color by sum of weights
        sumWeights = 1.0f / sumWeights;
        clr.x *= sumWeights;
        clr.y *= sumWeights;
        clr.z *= sumWeights;

        // Choose LERP quotient basing on how many texels
        // within the NLM window exceeded the weight threshold
        float lerpQ = (fCount > NLM_LERP_THRESHOLD) ? lerpC : 1.0f - lerpC;

        // Write final result to global memory
        float4 clr00          = tex2D<float4>(texImage, x, y);
        clr.x                 = lerpf(clr.x, clr00.x, lerpQ);
        clr.y                 = lerpf(clr.y, clr00.y, lerpQ);
        clr.z                 = lerpf(clr.z, clr00.z, lerpQ);
        dst[imageW * iy + ix] = make_color(clr.x, clr.y, clr.z, 0);
    }
}

extern "C" void cuda_NLM2(TColor *d_dst, int imageW, int imageH, float Noise, float LerpC, cudaTextureObject_t texImage)
{
    dim3 threads(BLOCKDIM_X, BLOCKDIM_Y);
    dim3 grid(iDivUp(imageW, BLOCKDIM_X), iDivUp(imageH, BLOCKDIM_Y));

    NLM2<<<grid, threads>>>(d_dst, imageW, imageH, Noise, LerpC, texImage);
}

////////////////////////////////////////////////////////////////////////////////
// Stripped NLM2 kernel, only highlighting areas with different LERP directions
////////////////////////////////////////////////////////////////////////////////
__global__ void NLM2diag(TColor *dst, int imageW, int imageH, float Noise, float LerpC, cudaTextureObject_t texImage)
{
    // Handle to thread block group
    cg::thread_block cta = cg::this_thread_block();

    // Weights cache
    __shared__ float fWeights[BLOCKDIM_X * BLOCKDIM_Y];

    const int ix = blockDim.x * blockIdx.x + threadIdx.x;
    const int iy = blockDim.y * blockIdx.y + threadIdx.y;
    // Add half of a texel to always address exact texel centers
    const float x  = (float)ix + 0.5f;
    const float y  = (float)iy + 0.5f;
    const float cx = blockDim.x * blockIdx.x + NLM_WINDOW_RADIUS + 0.5f;
    const float cy = blockDim.x * blockIdx.y + NLM_WINDOW_RADIUS + 0.5f;

    if (ix < imageW && iy < imageH) {
        // Find color distance from current texel to the center of NLM window
        float weight = 0;

        for (float n = -NLM_BLOCK_RADIUS; n <= NLM_BLOCK_RADIUS + 1; n++)
            for (float m = -NLM_BLOCK_RADIUS; m <= NLM_BLOCK_RADIUS + 1; m++)
                weight += vecLen(tex2D<float4>(texImage, cx + m, cy + n), tex2D<float4>(texImage, x + m, y + n));

        // Geometric distance from current texel to the center of NLM window
        float dist = (threadIdx.x - NLM_WINDOW_RADIUS) * (threadIdx.x - NLM_WINDOW_RADIUS)
                   + (threadIdx.y - NLM_WINDOW_RADIUS) * (threadIdx.y - NLM_WINDOW_RADIUS);

        // Derive final weight from color and geometric distance
        weight = __expf(-(weight * Noise + dist * INV_NLM_WINDOW_AREA));

        // Write the result to shared memory
        fWeights[threadIdx.y * BLOCKDIM_X + threadIdx.x] = weight;
        // Wait until all the weights are ready
        cg::sync(cta);

        // Normalized counter for the NLM weight threshold
        float fCount = 0;
        int   idx    = 0;

        // Cycle through NLM window, surrounding (x, y) texel
        for (float n = -NLM_WINDOW_RADIUS; n <= NLM_WINDOW_RADIUS + 1; n++)
            for (float m = -NLM_WINDOW_RADIUS; m <= NLM_WINDOW_RADIUS + 1; m++) {
                // Load precomputed weight
                float weightIJ = fWeights[idx++];

                // Update weight counter, if NLM weight for current window texel
                // exceeds the weight threshold
                fCount += (weightIJ > NLM_WEIGHT_THRESHOLD) ? INV_NLM_WINDOW_AREA : 0;
            }

        // Choose LERP quotient basing on how many texels
        // within the NLM window exceeded the weight threshold
        float lerpQ = (fCount > NLM_LERP_THRESHOLD) ? 1.0f : 0.0f;

        // Write final result to global memory
        dst[imageW * iy + ix] = make_color(lerpQ, 0, (1.0f - lerpQ), 0);
    };
}

extern "C" void
cuda_NLM2diag(TColor *d_dst, int imageW, int imageH, float Noise, float LerpC, cudaTextureObject_t texImage)
{
    dim3 threads(BLOCKDIM_X, BLOCKDIM_Y);
    dim3 grid(iDivUp(imageW, BLOCKDIM_X), iDivUp(imageH, BLOCKDIM_Y));

    NLM2diag<<<grid, threads>>>(d_dst, imageW, imageH, Noise, LerpC, texImage);
}
