create mipmaps

#version 450
#extension GL_ARB_shading_language_include : require
#extension GL_ARB_bindless_texture : require

#include "/buffer_blocks.glsl"

const uint g_UINT8_MAX = 0x000000FF;
const uint g_UINT10_MAX = 0x000003FF;
const float g_invUint8_max = 1.0 / float(g_UINT8_MAX);
const float g_invUint10_max = 1.0 / float(g_UINT10_MAX);

layout(location = 0) uniform int u_sourceLevel;
layout(location = 1) uniform int u_textureIndex;

layout(binding = 0, r32ui) uniform coherent uimage3D u_dstMip;

U_VOXELHANDLE_BLOCK(4);

void main()
{
    ivec3 dstSize = imageSize(u_dstMip);

    uint x = gl_VertexID;
    uint z = gl_InstanceID;

    for(uint y = 0; y < dstSize.y; ++y)
    {
        ivec3 dstPos = ivec3(x, y, z);
        ivec3 srcPos = dstPos * 2;

        uint srcColor = texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(0, 0, 0), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(1, 0, 0), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(0, 1, 0), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(1, 1, 0), u_sourceLevel).r;

        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(0, 0, 1), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(1, 0, 1), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(0, 1, 1), u_sourceLevel).r;
        srcColor += texelFetch(u_voxelTexture[u_textureIndex], srcPos + ivec3(1, 1, 1), u_sourceLevel).r;

        vec3 tmpColor;
        tmpColor.x = float(srcColor & g_UINT10_MAX);
        tmpColor.y = float((srcColor >> 10) & g_UINT10_MAX);
        tmpColor.z = float((srcColor >> 20) & g_UINT10_MAX);
        tmpColor = clamp(tmpColor, vec3(0.0), vec3(g_UINT10_MAX));

        tmpColor = tmpColor * g_invUint8_max / 8.0;

        tmpColor = round(tmpColor * g_UINT8_MAX);

        uint outColor = uint(tmpColor.x) | (uint(tmpColor.y) << 10) | (uint(tmpColor.z) << 20);

        imageStore(u_dstMip, dstPos, uvec4(outColor));
    }
}