/*
  Copyright (c) 2010-2023, Intel Corporation

  SPDX-License-Identifier: BSD-3-Clause
*/

#include "deferred.h"

struct InputDataArrays
{
    float *zBuffer;
    unsigned int16 *normalEncoded_x; // half float
    unsigned int16 *normalEncoded_y; // half float
    unsigned int16 *specularAmount; // half float
    unsigned int16 *specularPower; // half float
    unsigned int8 *albedo_x; // unorm8
    unsigned int8 *albedo_y; // unorm8
    unsigned int8 *albedo_z; // unorm8
    float *lightPositionView_x;
    float *lightPositionView_y;
    float *lightPositionView_z;
    float *lightAttenuationBegin;
    float *lightColor_x;
    float *lightColor_y;
    float *lightColor_z;
    float *lightAttenuationEnd;
};

struct InputHeader
{
    float cameraProj[4][4];
    float cameraNear;
    float cameraFar;

    int32 framebufferWidth;
    int32 framebufferHeight;
    int32 numLights;
    int32 inputDataChunkSize;
    int32 inputDataArrayOffsets[idaNum];
};


///////////////////////////////////////////////////////////////////////////
// Common utility routines

static inline float
dot3(float x, float y, float z, float a, float b, float c) {
    return (x*a + y*b + z*c);
}


static inline void
normalize3(float x, float y, float z, float &ox, float &oy, float &oz) {
    float n = rsqrt(x*x + y*y + z*z);
    ox = x * n;
    oy = y * n;
    oz = z * n;
}


static inline float
Unorm8ToFloat32(unsigned int8 u) {
    #pragma ignore warning(perf)
    return (float)u * (1.0f / 255.0f);
}


static inline unsigned int8
Float32ToUnorm8(float f) {
    #pragma ignore warning(perf)
    return (unsigned int8)(f * 255.0f);
}


static void
ComputeZBounds(
    uniform int32 tileStartX, uniform int32 tileEndX,
    uniform int32 tileStartY, uniform int32 tileEndY,
    // G-buffer data
    uniform float zBuffer[],
    uniform int32 gBufferWidth,
    // Camera data
    uniform float cameraProj_33, uniform float cameraProj_43,
    uniform float cameraNear, uniform float cameraFar,
    // Output
    uniform float &minZ,
    uniform float &maxZ
    )
{
    // Find Z bounds
    float laneMinZ = cameraFar;
    float laneMaxZ = cameraNear;
    for (uniform int32 y = tileStartY; y < tileEndY; ++y) {
        foreach (x = tileStartX ... tileEndX) {
            // Unproject depth buffer Z value into view space
            float z = zBuffer[y * gBufferWidth + x];
            float viewSpaceZ = cameraProj_43 / (z - cameraProj_33);

            // Work out Z bounds for our samples
            // Avoid considering skybox/background or otherwise invalid pixels
            if ((viewSpaceZ < cameraFar) && (viewSpaceZ >= cameraNear)) {
                laneMinZ = min(laneMinZ, viewSpaceZ);
                laneMaxZ = max(laneMaxZ, viewSpaceZ);
            }
        }
    }
    minZ = reduce_min(laneMinZ);
    maxZ = reduce_max(laneMaxZ);
}


export uniform int32
IntersectLightsWithTileMinMax(
    uniform int32 tileStartX, uniform int32 tileEndX,
    uniform int32 tileStartY, uniform int32 tileEndY,
    // Tile data
    uniform float minZ,
    uniform float maxZ,
    // G-buffer data
    uniform int32 gBufferWidth, uniform int32 gBufferHeight,
    // Camera data
    uniform float cameraProj_11, uniform float cameraProj_22,
    // Light Data
    uniform int32 numLights,
    uniform float light_positionView_x_array[],
    uniform float light_positionView_y_array[],
    uniform float light_positionView_z_array[],
    uniform float light_attenuationEnd_array[],
    // Output
    uniform int32 tileLightIndices[]
    )
{
    uniform float gBufferScale_x = 0.5f * (float)gBufferWidth;
    uniform float gBufferScale_y = 0.5f * (float)gBufferHeight;

    uniform float frustumPlanes_xy[4] = {
        -(cameraProj_11 * gBufferScale_x),
         (cameraProj_11 * gBufferScale_x),
         (cameraProj_22 * gBufferScale_y),
        -(cameraProj_22 * gBufferScale_y) };
    uniform float frustumPlanes_z[4] = {
         tileEndX - gBufferScale_x,
        -tileStartX + gBufferScale_x,
         tileEndY - gBufferScale_y,
        -tileStartY + gBufferScale_y };

    for (uniform int i = 0; i < 4; ++i) {
        uniform float norm = rsqrt(frustumPlanes_xy[i] * frustumPlanes_xy[i] +
                                   frustumPlanes_z[i] * frustumPlanes_z[i]);
        frustumPlanes_xy[i] *= norm;
        frustumPlanes_z[i] *= norm;
    }

    uniform int32 tileNumLights = 0;

    foreach (lightIndex = 0 ... numLights) {
        float light_positionView_z = light_positionView_z_array[lightIndex];
        float light_attenuationEnd = light_attenuationEnd_array[lightIndex];
        float light_attenuationEndNeg = -light_attenuationEnd;

        float d = light_positionView_z - minZ;
        bool inFrustum = (d >= light_attenuationEndNeg);

        d = maxZ - light_positionView_z;
        inFrustum = inFrustum && (d >= light_attenuationEndNeg);

        // This seems better than cif(!inFrustum) ccontinue; here since we
        // don't actually need to mask the rest of this function - this is
        // just a greedy early-out.  Could also structure all of this as
        // nested if() statements, but this a bit easier to read
        if (any(inFrustum)) {
            float light_positionView_x = light_positionView_x_array[lightIndex];
            float light_positionView_y = light_positionView_y_array[lightIndex];

            d = light_positionView_z * frustumPlanes_z[0] +
                light_positionView_x * frustumPlanes_xy[0];
            inFrustum = inFrustum && (d >= light_attenuationEndNeg);

            d = light_positionView_z * frustumPlanes_z[1] +
                light_positionView_x * frustumPlanes_xy[1];
            inFrustum = inFrustum && (d >= light_attenuationEndNeg);

            d = light_positionView_z * frustumPlanes_z[2] +
                light_positionView_y * frustumPlanes_xy[2];
            inFrustum = inFrustum && (d >= light_attenuationEndNeg);

            d = light_positionView_z * frustumPlanes_z[3] +
                light_positionView_y * frustumPlanes_xy[3];
            inFrustum = inFrustum && (d >= light_attenuationEndNeg);

            // Pack and store intersecting lights
            cif (inFrustum) {
                tileNumLights += packed_store_active(&tileLightIndices[tileNumLights],
                                                     lightIndex);
            }
        }
    }

    return tileNumLights;
}


static uniform int32
IntersectLightsWithTile(
    uniform int32 tileStartX, uniform int32 tileEndX,
    uniform int32 tileStartY, uniform int32 tileEndY,
    uniform int32 gBufferWidth, uniform int32 gBufferHeight,
    // G-buffer data
    uniform float zBuffer[],
    // Camera data
    uniform float cameraProj_11, uniform float cameraProj_22,
    uniform float cameraProj_33, uniform float cameraProj_43,
    uniform float cameraNear, uniform float cameraFar,
    // Light Data
    uniform int32 numLights,
    uniform float light_positionView_x_array[],
    uniform float light_positionView_y_array[],
    uniform float light_positionView_z_array[],
    uniform float light_attenuationEnd_array[],
    // Output
    uniform int32 tileLightIndices[]
    )
{
    uniform float minZ, maxZ;
    ComputeZBounds(tileStartX, tileEndX, tileStartY, tileEndY,
        zBuffer, gBufferWidth, cameraProj_33, cameraProj_43, cameraNear, cameraFar,
        minZ, maxZ);

    uniform int32 tileNumLights = IntersectLightsWithTileMinMax(
        tileStartX, tileEndX, tileStartY, tileEndY, minZ, maxZ,
        gBufferWidth, gBufferHeight, cameraProj_11, cameraProj_22,
        MAX_LIGHTS, light_positionView_x_array, light_positionView_y_array,
        light_positionView_z_array, light_attenuationEnd_array,
        tileLightIndices);

    return tileNumLights;
}


export void
ShadeTile(
    uniform int32 tileStartX, uniform int32 tileEndX,
    uniform int32 tileStartY, uniform int32 tileEndY,
    uniform int32 gBufferWidth, uniform int32 gBufferHeight,
    uniform InputDataArrays &inputData,
    // Camera data
    uniform float cameraProj_11, uniform float cameraProj_22,
    uniform float cameraProj_33, uniform float cameraProj_43,
    // Light list
    uniform int32 tileLightIndices[],
    uniform int32 tileNumLights,
    // UI
    uniform bool visualizeLightCount,
    // Output
    uniform unsigned int8 framebuffer_r[],
    uniform unsigned int8 framebuffer_g[],
    uniform unsigned int8 framebuffer_b[]
    )
{
    if (tileNumLights == 0 || visualizeLightCount) {
        uniform unsigned int8 c = (unsigned int8)(min(tileNumLights << 2, 255));
        for (uniform int32 y = tileStartY; y < tileEndY; ++y) {
            foreach (x = tileStartX ... tileEndX) {
                int32 framebufferIndex = (y * gBufferWidth + x);
                framebuffer_r[framebufferIndex] = c;
                framebuffer_g[framebufferIndex] = c;
                framebuffer_b[framebufferIndex] = c;
            }
        }
    } else {
        uniform float twoOverGBufferWidth = 2.0f / gBufferWidth;
        uniform float twoOverGBufferHeight = 2.0f / gBufferHeight;

        for (uniform int32 y = tileStartY; y < tileEndY; ++y) {
            uniform float positionScreen_y = -(((0.5f + y) * twoOverGBufferHeight) - 1.f);

            foreach (x = tileStartX ... tileEndX) {
                int32 gBufferOffset = y * gBufferWidth + x;

                // Reconstruct position and (negative) view vector from G-buffer
                float surface_positionView_x, surface_positionView_y, surface_positionView_z;
                float Vneg_x, Vneg_y, Vneg_z;

                float z = inputData.zBuffer[gBufferOffset];

                // Compute screen/clip-space position
                // NOTE: Mind DX11 viewport transform and pixel center!
                float positionScreen_x = (0.5f + (float)(x)) *
                    twoOverGBufferWidth - 1.0f;

                // Unproject depth buffer Z value into view space
                surface_positionView_z = cameraProj_43 / (z - cameraProj_33);
                surface_positionView_x = positionScreen_x * surface_positionView_z /
                    cameraProj_11;
                surface_positionView_y = positionScreen_y * surface_positionView_z /
                    cameraProj_22;

                // We actually end up with a vector pointing *at* the
                // surface (i.e. the negative view vector)
                normalize3(surface_positionView_x, surface_positionView_y,
                           surface_positionView_z, Vneg_x, Vneg_y, Vneg_z);

                // Reconstruct normal from G-buffer
                float surface_normal_x, surface_normal_y, surface_normal_z;
                float normal_x = half_to_float(inputData.normalEncoded_x[gBufferOffset]);
                float normal_y = half_to_float(inputData.normalEncoded_y[gBufferOffset]);

                float f = (normal_x - normal_x * normal_x) + (normal_y - normal_y * normal_y);
                float m = sqrt(4.0f * f - 1.0f);

                surface_normal_x = m * (4.0f * normal_x - 2.0f);
                surface_normal_y = m * (4.0f * normal_y - 2.0f);
                surface_normal_z = 3.0f - 8.0f * f;

                // Load other G-buffer parameters
                float surface_specularAmount =
                    half_to_float(inputData.specularAmount[gBufferOffset]);
                float surface_specularPower  =
                    half_to_float(inputData.specularPower[gBufferOffset]);
                float surface_albedo_x = Unorm8ToFloat32(inputData.albedo_x[gBufferOffset]);
                float surface_albedo_y = Unorm8ToFloat32(inputData.albedo_y[gBufferOffset]);
                float surface_albedo_z = Unorm8ToFloat32(inputData.albedo_z[gBufferOffset]);

                float lit_x = 0.0f;
                float lit_y = 0.0f;
                float lit_z = 0.0f;
                for (uniform int32 tileLightIndex = 0; tileLightIndex < tileNumLights;
                     ++tileLightIndex) {
                    uniform int32 lightIndex = tileLightIndices[tileLightIndex];

                    // Gather light data relevant to initial culling
                    uniform float light_positionView_x =
                        inputData.lightPositionView_x[lightIndex];
                    uniform float light_positionView_y =
                        inputData.lightPositionView_y[lightIndex];
                    uniform float light_positionView_z =
                        inputData.lightPositionView_z[lightIndex];
                    uniform float light_attenuationEnd =
                        inputData.lightAttenuationEnd[lightIndex];

                    // Compute light vector
                    float L_x = light_positionView_x - surface_positionView_x;
                    float L_y = light_positionView_y - surface_positionView_y;
                    float L_z = light_positionView_z - surface_positionView_z;

                    float distanceToLight2 = dot3(L_x, L_y, L_z, L_x, L_y, L_z);

                    // Clip at end of attenuation
                    float light_attenutaionEnd2 = light_attenuationEnd * light_attenuationEnd;

                    cif (distanceToLight2 < light_attenutaionEnd2) {
                        float distanceToLight = sqrt(distanceToLight2);

                        // HLSL "rcp" is allowed to be fairly inaccurate
                        float distanceToLightRcp = rcp(distanceToLight);
                        L_x *= distanceToLightRcp;
                        L_y *= distanceToLightRcp;
                        L_z *= distanceToLightRcp;

                        // Start computing brdf
                        float NdotL = dot3(surface_normal_x, surface_normal_y,
                                           surface_normal_z, L_x, L_y, L_z);

                        // Clip back facing
                        cif (NdotL > 0.0f) {
                            uniform float light_attenuationBegin =
                                inputData.lightAttenuationBegin[lightIndex];

                            // Light distance attenuation (linstep)
                            float lightRange = (light_attenuationEnd - light_attenuationBegin);
                            float falloffPosition = (light_attenuationEnd - distanceToLight);
                            float attenuation = min(falloffPosition / lightRange, 1.0f);

                            float H_x = (L_x - Vneg_x);
                            float H_y = (L_y - Vneg_y);
                            float H_z = (L_z - Vneg_z);
                            normalize3(H_x, H_y, H_z, H_x, H_y, H_z);

                            float NdotH = dot3(surface_normal_x, surface_normal_y,
                                               surface_normal_z, H_x, H_y, H_z);
                            NdotH = max(NdotH, 0.0f);

                            float specular = pow(NdotH, surface_specularPower);
                            float specularNorm = (surface_specularPower + 2.0f) *
                                (1.0f / 8.0f);
                            float specularContrib = surface_specularAmount *
                                specularNorm * specular;

                            float k = attenuation * NdotL * (1.0f + specularContrib);

                            uniform float light_color_x = inputData.lightColor_x[lightIndex];
                            uniform float light_color_y = inputData.lightColor_y[lightIndex];
                            uniform float light_color_z = inputData.lightColor_z[lightIndex];

                            float lightContrib_x = surface_albedo_x * light_color_x;
                            float lightContrib_y = surface_albedo_y * light_color_y;
                            float lightContrib_z = surface_albedo_z * light_color_z;

                            lit_x += lightContrib_x * k;
                            lit_y += lightContrib_y * k;
                            lit_z += lightContrib_z * k;
                        }
                    }
                }

                // Gamma correct
                // These pows are pretty slow right now, but we can do
                // something faster if really necessary to squeeze every
                // last bit of performance out of it
                float gamma = 1.0 / 2.2f;
                lit_x = pow(clamp(lit_x, 0.0f, 1.0f), gamma);
                lit_y = pow(clamp(lit_y, 0.0f, 1.0f), gamma);
                lit_z = pow(clamp(lit_z, 0.0f, 1.0f), gamma);

                framebuffer_r[gBufferOffset] = Float32ToUnorm8(lit_x);
                framebuffer_g[gBufferOffset] = Float32ToUnorm8(lit_y);
                framebuffer_b[gBufferOffset] = Float32ToUnorm8(lit_z);
            }
        }
    }
}


///////////////////////////////////////////////////////////////////////////
// Static decomposition

task void
RenderTile(uniform int num_groups_x, uniform int num_groups_y,
           uniform InputHeader &inputHeader,
           uniform InputDataArrays &inputData,
           uniform int visualizeLightCount,
           // Output
           uniform unsigned int8 framebuffer_r[],
           uniform unsigned int8 framebuffer_g[],
           uniform unsigned int8 framebuffer_b[]) {
    uniform int32 group_y = taskIndex / num_groups_x;
    uniform int32 group_x = taskIndex % num_groups_x;
    uniform int32 tile_start_x = group_x * MIN_TILE_WIDTH;
    uniform int32 tile_start_y = group_y * MIN_TILE_HEIGHT;
    uniform int32 tile_end_x = tile_start_x + MIN_TILE_WIDTH;
    uniform int32 tile_end_y = tile_start_y + MIN_TILE_HEIGHT;

    uniform int framebufferWidth = inputHeader.framebufferWidth;
    uniform int framebufferHeight = inputHeader.framebufferHeight;
    uniform float cameraProj_00 = inputHeader.cameraProj[0][0];
    uniform float cameraProj_11 = inputHeader.cameraProj[1][1];
    uniform float cameraProj_22 = inputHeader.cameraProj[2][2];
    uniform float cameraProj_32 = inputHeader.cameraProj[3][2];

    // Light intersection: figure out which lights illuminate this tile.
    uniform int tileLightIndices[MAX_LIGHTS];  // Light list for the tile
    uniform int numTileLights =
        IntersectLightsWithTile(tile_start_x, tile_end_x,
                                tile_start_y, tile_end_y,
                                framebufferWidth, framebufferHeight,
                                inputData.zBuffer,
                                cameraProj_00, cameraProj_11,
                                cameraProj_22, cameraProj_32,
                                inputHeader.cameraNear, inputHeader.cameraFar,
                                MAX_LIGHTS,
                                inputData.lightPositionView_x,
                                inputData.lightPositionView_y,
                                inputData.lightPositionView_z,
                                inputData.lightAttenuationEnd,
                                tileLightIndices);

    // And now shade the tile, using the lights in tileLightIndices
    ShadeTile(tile_start_x, tile_end_x, tile_start_y, tile_end_y,
              framebufferWidth, framebufferHeight, inputData,
              cameraProj_00, cameraProj_11, cameraProj_22, cameraProj_32,
              tileLightIndices, numTileLights, visualizeLightCount,
              framebuffer_r, framebuffer_g, framebuffer_b);
}


export void
RenderStatic(uniform InputHeader &inputHeader,
             uniform InputDataArrays &inputData,
             uniform int visualizeLightCount,
             // Output
             uniform unsigned int8 framebuffer_r[],
             uniform unsigned int8 framebuffer_g[],
             uniform unsigned int8 framebuffer_b[]) {
    uniform int num_groups_x = (inputHeader.framebufferWidth +
                                MIN_TILE_WIDTH - 1) / MIN_TILE_WIDTH;
    uniform int num_groups_y = (inputHeader.framebufferHeight +
                                MIN_TILE_HEIGHT - 1) / MIN_TILE_HEIGHT;
    uniform int num_groups = num_groups_x * num_groups_y;

    // Launch a task to render each tile, each of which is MIN_TILE_WIDTH
    // by MIN_TILE_HEIGHT pixels.
    launch[num_groups] RenderTile(num_groups_x, num_groups_y,
                                  inputHeader, inputData, visualizeLightCount,
                                  framebuffer_r, framebuffer_g, framebuffer_b);
}


///////////////////////////////////////////////////////////////////////////
// Routines for dynamic decomposition path

// This computes the z min/max range for a whole row worth of tiles.
export void
ComputeZBoundsRow(
    uniform int32 tileY,
    uniform int32 tileWidth, uniform int32 tileHeight,
    uniform int32 numTilesX, uniform int32 numTilesY,
    // G-buffer data
    uniform float zBuffer[],
    uniform int32 gBufferWidth,
    // Camera data
    uniform float cameraProj_33, uniform float cameraProj_43,
    uniform float cameraNear, uniform float cameraFar,
    // Output
    uniform float minZArray[],
    uniform float maxZArray[]
    )
{
    for (uniform int32 tileX = 0; tileX < numTilesX; ++tileX) {
        uniform float minZ, maxZ;
        ComputeZBounds(
            tileX * tileWidth, tileX * tileWidth + tileWidth,
            tileY * tileHeight, tileY * tileHeight + tileHeight,
            zBuffer, gBufferWidth,
            cameraProj_33, cameraProj_43, cameraNear, cameraFar,
            minZ, maxZ);
        minZArray[tileX] = minZ;
        maxZArray[tileX] = maxZ;
    }
}


// Reclassifies the lights with respect to four sub-tiles when we refine a tile.
// numLights need not be a multiple of programCount here, but the input and output arrays
// should be able to handle programCount-sized load/stores.
export void
SplitTileMinMax(
    uniform int32 tileMidX, uniform int32 tileMidY,
    // Subtile data (00, 10, 01, 11)
    uniform float subtileMinZ[],
    uniform float subtileMaxZ[],
    // G-buffer data
    uniform int32 gBufferWidth, uniform int32 gBufferHeight,
    // Camera data
    uniform float cameraProj_11, uniform float cameraProj_22,
    // Light Data
    uniform int32 lightIndices[],
    uniform int32 numLights,
    uniform float light_positionView_x_array[],
    uniform float light_positionView_y_array[],
    uniform float light_positionView_z_array[],
    uniform float light_attenuationEnd_array[],
    // Outputs
    uniform int32 subtileIndices[],
    uniform int32 subtileIndicesPitch,
    uniform int32 subtileNumLights[]
    )
{
    uniform float gBufferScale_x = 0.5f * (float)gBufferWidth;
    uniform float gBufferScale_y = 0.5f * (float)gBufferHeight;

    uniform float frustumPlanes_xy[2] = { -(cameraProj_11 * gBufferScale_x),
                                           (cameraProj_22 * gBufferScale_y) };
    uniform float frustumPlanes_z[2] = { tileMidX - gBufferScale_x,
                                         tileMidY - gBufferScale_y };

    // Normalize
    uniform float norm[2] = { rsqrt(frustumPlanes_xy[0] * frustumPlanes_xy[0] +
                                    frustumPlanes_z[0] * frustumPlanes_z[0]),
                              rsqrt(frustumPlanes_xy[1] * frustumPlanes_xy[1] +
                                    frustumPlanes_z[1] * frustumPlanes_z[1]) };
    frustumPlanes_xy[0] *= norm[0];
    frustumPlanes_xy[1] *= norm[1];
    frustumPlanes_z[0] *= norm[0];
    frustumPlanes_z[1] *= norm[1];

    // Initialize
    uniform int32 subtileLightOffset[4];
    subtileLightOffset[0] = 0 * subtileIndicesPitch;
    subtileLightOffset[1] = 1 * subtileIndicesPitch;
    subtileLightOffset[2] = 2 * subtileIndicesPitch;
    subtileLightOffset[3] = 3 * subtileIndicesPitch;

    foreach (i = 0 ... numLights) {
        int32 lightIndex = lightIndices[i];

        #pragma ignore warning(perf)
        float light_positionView_x = light_positionView_x_array[lightIndex];
        #pragma ignore warning(perf)
        float light_positionView_y = light_positionView_y_array[lightIndex];
        #pragma ignore warning(perf)
        float light_positionView_z = light_positionView_z_array[lightIndex];
        #pragma ignore warning(perf)
        float light_attenuationEnd = light_attenuationEnd_array[lightIndex];
        float light_attenuationEndNeg = -light_attenuationEnd;

        // Test lights again subtile z bounds
        bool inFrustum[4];
        inFrustum[0] = (light_positionView_z - subtileMinZ[0] >= light_attenuationEndNeg) &&
            (subtileMaxZ[0] - light_positionView_z >= light_attenuationEndNeg);
        inFrustum[1] = (light_positionView_z - subtileMinZ[1] >= light_attenuationEndNeg) &&
            (subtileMaxZ[1] - light_positionView_z >= light_attenuationEndNeg);
        inFrustum[2] = (light_positionView_z - subtileMinZ[2] >= light_attenuationEndNeg) &&
            (subtileMaxZ[2] - light_positionView_z >= light_attenuationEndNeg);
        inFrustum[3] = (light_positionView_z - subtileMinZ[3] >= light_attenuationEndNeg) &&
            (subtileMaxZ[3] - light_positionView_z >= light_attenuationEndNeg);

        float dx = light_positionView_z * frustumPlanes_z[0] +
            light_positionView_x * frustumPlanes_xy[0];
        float dy = light_positionView_z * frustumPlanes_z[1] +
            light_positionView_y * frustumPlanes_xy[1];

        cif (abs(dx) > light_attenuationEnd) {
            bool positiveX = dx > 0.0f;
            inFrustum[0] = inFrustum[0] &&  positiveX;    // 00 subtile
            inFrustum[1] = inFrustum[1] && !positiveX;    // 10 subtile
            inFrustum[2] = inFrustum[2] &&  positiveX;    // 01 subtile
            inFrustum[3] = inFrustum[3] && !positiveX;    // 11 subtile
        }
        cif (abs(dy) > light_attenuationEnd) {
            bool positiveY = dy > 0.0f;
            inFrustum[0] = inFrustum[0] &&  positiveY;    // 00 subtile
            inFrustum[1] = inFrustum[1] &&  positiveY;    // 10 subtile
            inFrustum[2] = inFrustum[2] && !positiveY;    // 01 subtile
            inFrustum[3] = inFrustum[3] && !positiveY;    // 11 subtile
        }

        // Pack and store intersecting lights
        // TODO: Experiment with a loop here instead
        cif (inFrustum[0])
            subtileLightOffset[0] +=
            packed_store_active(&subtileIndices[subtileLightOffset[0]],
                                lightIndex);
        cif (inFrustum[1])
            subtileLightOffset[1] +=
            packed_store_active(&subtileIndices[subtileLightOffset[1]],
                                lightIndex);
        cif (inFrustum[2])
            subtileLightOffset[2] +=
            packed_store_active(&subtileIndices[subtileLightOffset[2]],
                                lightIndex);
        cif (inFrustum[3])
            subtileLightOffset[3] +=
            packed_store_active(&subtileIndices[subtileLightOffset[3]],
                                lightIndex);
    }

    subtileNumLights[0] = subtileLightOffset[0] - 0 * subtileIndicesPitch;
    subtileNumLights[1] = subtileLightOffset[1] - 1 * subtileIndicesPitch;
    subtileNumLights[2] = subtileLightOffset[2] - 2 * subtileIndicesPitch;
    subtileNumLights[3] = subtileLightOffset[3] - 3 * subtileIndicesPitch;
}