RecursionSolution.hlsl

// This file is part of the AMD & HSC Work Graph Playground.
//
// Copyright (C) 2025 Advanced Micro Devices, Inc. and Coburg University of Applied Sciences and Arts.
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#include "Common.h"

struct Line
{
    float2 a, b;
};

// [Task 2 Solution]:
struct Box
{
    float2 topLeft;
    float size;
};

[Shader("node")]
[NodeIsProgramEntry]
[NodeLaunch("thread")]
[NodeId("Entry")]
void EntryNode(
    [MaxRecords(3)]
    [NodeId("Snowflake")]
    NodeOutput<Line> snowflakeOutput,

    // [Task 2 Solution]: Single record output to the "Sponge" node.
    [MaxRecords(1)]
    [NodeId("Sponge")]
    NodeOutput<Box> spongeOutput
){
    const bool   stackVertical = RenderSize.x > RenderSize.y;
    const float  scale         = stackVertical? min(RenderSize.x * .225, RenderSize.y * .45) :
                                                min(RenderSize.x * .45, RenderSize.y * .225);
    // Draw Snowflake fractal.
    {
        const float2 snowflakeCenter = RenderSize * (stackVertical? float2(.25, .5) : float2(.5, .25));

        // Request three output records for the three sides of the initial equilateral triangle.
        ThreadNodeOutputRecords<Line> outputRecords =
            snowflakeOutput.GetThreadNodeOutputRecords(3);

        // Compute three vertices of the initial equilateral triangle.
        const float2 v0 = snowflakeCenter + scale * float2(0., -1.);
        const float2 v1 = snowflakeCenter + scale * float2(-sqrt(3) * .5, .5);
        const float2 v2 = snowflakeCenter + scale * float2(+sqrt(3) * .5, .5);

        // Create the initial equilateral triangle.
        outputRecords.Get(0).a = v0;
        outputRecords.Get(0).b = v1;

        outputRecords.Get(1).a = v1;
        outputRecords.Get(2).a = v2;

        outputRecords.Get(2).b = v0;
        outputRecords.Get(1).b = v2;

        outputRecords.OutputComplete();
    }

    // Draw Sponge fractal.
    {
        const float2 spongeCenter = RenderSize * (stackVertical? float2(.75, .5) : float2(.5, .75));

        // [Solution 2]: Request a single record for the "Sponge" node and write the initial box
        //               position and size to it.
        ThreadNodeOutputRecords<Box> outputRecord = spongeOutput.GetThreadNodeOutputRecords(1);

        outputRecord.Get().topLeft = spongeCenter - scale;
        outputRecord.Get().size = 2 * scale;

        outputRecord.OutputComplete();
    }
}

[Shader("node")]
[NodeLaunch("thread")]
// If a node declares a recursive output to itself (see "recursiveOutput" below),
// a "[NodeMaxRecursionDepth(...)]" is required to specify the maximum number of recursion levels.
// This is required, as each recursion level counts towards the total graph depth,
// and the runtime has to ensure that this depth does not exceed the limit of 32 nodes.
// We can use "GetRemainingRecursionLevels()" in the node function to query the remaining
// recursion levels, i.e., determine whether we can still request recursive output records.
[NodeMaxRecursionDepth(4)]
[NodeId("Snowflake")]
void SnowflakeNode(
    ThreadNodeInputRecord<Line> inputRecord,

    [MaxRecords(4)]
    [NodeId("Snowflake")]
    NodeOutput<Line> recursiveOutput
)
{
    const float2 a = inputRecord.Get().a;
    const float2 b = inputRecord.Get().b;

    // Check if we have reached the recursion limit.
    const bool hasOutput = GetRemainingRecursionLevels() != 0;

    // Each recursion level has a 4x amplification factor, as each line
    // splits into four new lines.
    ThreadNodeOutputRecords<Line> outputRecords =
        recursiveOutput.GetThreadNodeOutputRecords(hasOutput * 4);

    if (hasOutput) {
        // Perpendicular vector to current line segment.
        const float2 perp = float2(a.y - b.y, b.x - a.x) * sqrt(3) / 6;

        // Compute vertices for the four new line segments:
        //
        //             v2
        //            /  \
        //           /    \
        // v0 ---- v1      v3 ---- v4
        const float2 v0 = a;
        const float2 v1 = lerp(a, b, 1./3.);
        const float2 v2 = lerp(a, b, .5) + perp;
        const float2 v3 = lerp(a, b, 2./3.);
        const float2 v4 = b;

        outputRecords.Get(0).a = v0;
        outputRecords.Get(0).b = v1;

        outputRecords.Get(1).a = v1;
        outputRecords.Get(1).b = v2;

        outputRecords.Get(2).a = v2;
        outputRecords.Get(2).b = v3;

        outputRecords.Get(3).a = v3;
        outputRecords.Get(3).b = v4;
    } else {
        // We've reached the recursion limit, thus we draw the current line segment
        // to the output.
        DrawLine(a, b);
    }

    outputRecords.OutputComplete();
}

// [Task 2 Solution]:
[Shader("node")]
[NodeLaunch("thread")]
[NodeMaxRecursionDepth(4)]
[NodeId("Sponge")]
void SpongeNode(
    ThreadNodeInputRecord<Box> inputRecord,

    [MaxRecords(8)]
    [NodeId("Sponge")]
    NodeOutput<Box> recursiveOutput
)
{
    const float2 topLeft = inputRecord.Get().topLeft;
    const float  size    = inputRecord.Get().size;

    // Check if we have reached the recursion limit.
    const bool hasOutput = GetRemainingRecursionLevels() != 0;

    // Split each box into eight boxes:
    // +---+---+---+
    // | 0 | 1 | 2 |
    // +---+---+---+
    // | 3 |   | 4 |
    // +---+---+---+
    // | 5 | 6 | 7 |
    // +---+---+---+
    ThreadNodeOutputRecords<Box> outputRecords
        = recursiveOutput.GetThreadNodeOutputRecords(hasOutput * 8);

    if (hasOutput) {
        const float newSize = size / 3.;

        uint outputRecordIndex = 0;

        for(uint row = 0; row < 3;  ++row){
            for(uint col = 0; col < 3; ++col){
                // Skip the center (see visualization above).
                if(row == 1 && col == 1) continue;

                outputRecords.Get(outputRecordIndex).size    = newSize;
                outputRecords.Get(outputRecordIndex).topLeft = topLeft + float2(col * newSize, row * newSize);

                // Advance to next output record.
                outputRecordIndex++;
            }
        }
    } else {
        // We've reached the recursion limit, thus we draw the current box to the output.
        FillRect(topLeft, topLeft + size);
    }

    outputRecords.OutputComplete();
}