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fix(shaders_lab): cycle check uses real reachability, not vector index

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Previously the cycle validator rejected any link whose source had a
vector index >= target's, which silently killed legitimate connections
between nodes added in the wrong drop order.

Switch to a DFS over source_ids: an edge from->to creates a cycle iff
`from` already (transitively) depends on `to`. topo_sort runs after
each topology change so the vector ends up in a consistent order
regardless of how nodes were inserted.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Egutierrez
2026-04-25 01:37:50 +02:00
parent c2e4f6a9e1
commit 144b15f0ce
2 changed files with 32 additions and 7 deletions
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apps/shaders_lab/shaders_lab.exe
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cpp/functions/gfx/dag_node_editor.cpp
+32 -7
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@@ -4,6 +4,7 @@
#include "imgui_node_editor.h"
#include <algorithm>
#include <cstdio>
#include <functional>
#include <queue>
#include <string>
#include <unordered_map>
@@ -325,14 +326,38 @@ bool dag_node_editor(std::vector<DagStep>& pipeline) {
int from_idx = find_by_uid(pipeline, from_uid);
int to_idx = find_by_uid(pipeline, to_uid);
// Reject cycles: in topo-ordered list, from must come before to.
// We also reject self-loops.
// Real cycle check: would the new edge from->to introduce a path
// from `from` back to itself? It does iff `from` already (transitively)
// depends on `to`. We walk source_ids of `from` and reject if we
// ever hit `to`. Vector index order is irrelevant — topo_sort runs
// at end-of-frame and reorders the pipeline.
bool cycle = false;
if (from_uid == to_uid) {
ed::RejectNewItem(ImVec4(1, 0, 0, 1));
valid = false;
} else if (from_idx >= to_idx) {
// Would create a back-edge; reject
ed::RejectNewItem(ImVec4(1, 0.5f, 0, 1));
cycle = true;
} else if (from_idx >= 0 && to_idx >= 0) {
const std::string to_id = pipeline[static_cast<size_t>(to_idx)].id;
std::function<bool(const std::string&)> depends_on_to;
depends_on_to = [&](const std::string& node_id) -> bool {
if (node_id == to_id) return true;
int idx = -1;
for (int i = 0; i < static_cast<int>(pipeline.size()); ++i) {
if (pipeline[static_cast<size_t>(i)].id == node_id) { idx = i; break; }
}
if (idx < 0) return false;
const DagStep& s = pipeline[static_cast<size_t>(idx)];
const DagNodeDef* d = dag_find(s.name);
int n = d ? d->num_inputs : 0;
for (int k = 0; k < n; ++k) {
const std::string& sid = s.source_ids[static_cast<size_t>(k)];
if (!sid.empty() && depends_on_to(sid)) return true;
}
return false;
};
cycle = depends_on_to(pipeline[static_cast<size_t>(from_idx)].id);
}
if (cycle) {
ed::RejectNewItem(ImVec4(1, 0.3f, 0.3f, 1));
valid = false;
}