From 67f0169fa7983f531d38cbcb548bcf9c9e5b1cf2 Mon Sep 17 00:00:00 2001
From: codereader <greebo@angua.at>
Date: Tue, 23 Mar 2021 07:20:09 +0100
Subject: [PATCH] #5571: Fix table lookup implementation (snapped)

---
 radiantcore/shaders/TableDefinition.cpp | 11 ++++----
 test/Materials.cpp                      | 36 ++++++++++++++++++++++++-
 test/resources/tdm/materials/tables.mtr |  1 +
 3 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/radiantcore/shaders/TableDefinition.cpp b/radiantcore/shaders/TableDefinition.cpp
index 0a35b268d7..d50f7a6dfb 100644
--- a/radiantcore/shaders/TableDefinition.cpp
+++ b/radiantcore/shaders/TableDefinition.cpp
@@ -63,16 +63,15 @@ float TableDefinition::getValue(float index)
 		index *= numValues;
 	}
 
-	// If snap is active, round the values to the nearest integer
+    auto leftIdx = static_cast<std::size_t>(std::floor(index)) % numValues;
+
 	if (_snap)
 	{
-		index = std::floor(index + 0.5f);
-
-		return _values[static_cast<std::size_t>(index) % numValues];
+	    // If snap is active, just use the left-bound index
+		return _values[leftIdx];
 	}
 
-	// No snapping, pick the interpolation values
-	auto leftIdx = static_cast<std::size_t>(std::floor(index)) % numValues;
+	// No snapping, pick the next value to the right to interpolate
 	auto rightIdx = (leftIdx + 1) % numValues;
 
 	float fraction = index - leftIdx;
diff --git a/test/Materials.cpp b/test/Materials.cpp
index 9035d0df50..da7d69ebaf 100644
--- a/test/Materials.cpp
+++ b/test/Materials.cpp
@@ -119,7 +119,7 @@ void performLookupTests(const ITableDefinition::Ptr& table, const std::vector<st
     }
 }
 
-TEST_F(MaterialsTest, MaterialTableLookupNonSnapped)
+TEST_F(MaterialsTest, MaterialTableLookup)
 {
     auto table = GlobalMaterialManager().getTable("sinTable");
 
@@ -147,6 +147,40 @@ TEST_F(MaterialsTest, MaterialTableLookupNonSnapped)
     performLookupTests(table, testCases);
 }
 
+TEST_F(MaterialsTest, MaterialTableLookupSnapped)
+{
+    auto table = GlobalMaterialManager().getTable("snapTest");
+
+    std::vector<std::pair<float, float>> testCases
+    {
+      {  -9.400000f, 1.000000f },
+      {  -1.000000f, 1.000000f },
+      {  -0.355500f, 0.000000f },
+      {  -0.000025f, 0.000000f },
+      {   0.000000f, 1.000000f },
+      {   0.000025f, 1.000000f },
+      {   0.050000f, 0.000000f },
+      {   0.250000f, 0.000000f },
+      {   0.332200f, 1.000000f },
+      {   0.400000f, 1.000000f },
+      {   0.430000f, 1.000000f },
+      {   0.450000f, 1.000000f },
+      {   0.460000f, 1.000000f },
+      {   0.490000f, 0.000000f },
+      {   0.700020f, 0.000000f },
+      {   0.910000f, 0.000000f },
+      {   0.999980f, 0.000000f },
+      {   1.000000f, 1.000000f },
+      {   1.002000f, 1.000000f },
+      {   1.800000f, 0.000000f },
+      {   2.300000f, 1.000000f },
+      {  60.500000f, 0.000000f },
+      { 100.230003f, 0.000000f },
+    };
+
+    performLookupTests(table, testCases);
+}
+
 TEST_F(MaterialsTest, MaterialTableLookupClamped)
 {
     auto table = GlobalMaterialManager().getTable("clampTest");
diff --git a/test/resources/tdm/materials/tables.mtr b/test/resources/tdm/materials/tables.mtr
index 0a6f396d37..e97943101a 100644
--- a/test/resources/tdm/materials/tables.mtr
+++ b/test/resources/tdm/materials/tables.mtr
@@ -67,3 +67,4 @@ table cosTable { {
 0.980785, 0.985278, 0.989177, 0.992480, 0.995185, 0.997290, 0.998795, 0.999699 } }
 
 table clampTest { clamp { 1, 1, 1, 1, 1, 1, 1, 1, 1, 0 } }
+table snapTest { snap { 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0 } }
\ No newline at end of file