1 files changed, 45 insertions, 15 deletions

diff --git a/src/gui/painting/qcolortransfertable_p.h b/src/gui/painting/qcolortransfertable_p.h
index ac1f843912..51c9cff6d6 100644
--- a/src/gui/painting/qcolortransfertable_p.h
+++ b/src/gui/painting/qcolortransfertable_p.h
@@ -29,25 +29,38 @@ QT_BEGIN_NAMESPACE
 class Q_GUI_EXPORT QColorTransferTable
 {
 public:
-    QColorTransferTable() noexcept
-            : m_tableSize(0)
-    { }
-    QColorTransferTable(uint32_t size, const QList<uint8_t> &table) noexcept
-        : m_tableSize(size), m_table8(table)
+    enum Type : uint8_t {
+        TwoWay = 0,
+        OneWay,
+    };
+    QColorTransferTable() noexcept = default;
+    QColorTransferTable(uint32_t size, const QList<uint8_t> &table, Type type = TwoWay) noexcept
+        : m_type(type), m_tableSize(size), m_table8(table)
     {
-        Q_ASSERT(qsizetype(size) <= table.count());
+        Q_ASSERT(qsizetype(size) <= table.size());
     }
-    QColorTransferTable(uint32_t size, const QList<uint16_t> &table) noexcept
-        : m_tableSize(size), m_table16(table)
+    QColorTransferTable(uint32_t size, const QList<uint16_t> &table, Type type = TwoWay) noexcept
+        : m_type(type), m_tableSize(size), m_table16(table)
     {
-        Q_ASSERT(qsizetype(size) <= table.count());
+        Q_ASSERT(qsizetype(size) <= table.size());
     }
 
-    bool isEmpty() const
+    bool isEmpty() const noexcept
     {
         return m_tableSize == 0;
     }
 
+    bool isIdentity() const
+    {
+        if (isEmpty())
+            return true;
+        if (m_tableSize != 2)
+            return false;
+        if (!m_table8.isEmpty())
+            return m_table8[0] == 0 && m_table8[1] == 255;
+        return m_table16[0] == 0 && m_table16[1] == 65535;
+    }
+
     bool checkValidity() const
     {
         if (isEmpty())
@@ -58,7 +71,11 @@ public:
         // At least 2 elements
         if (m_tableSize < 2)
             return false;
-        // The table must describe an injective curve:
+        return (m_type == OneWay) || checkInvertibility();
+    }
+    bool checkInvertibility() const
+    {
+        // The two-way tables must describe an injective curve:
         if (!m_table8.isEmpty()) {
             uint8_t val = 0;
             for (uint i = 0; i < m_tableSize; ++i) {
@@ -80,15 +97,17 @@ public:
 
     float apply(float x) const
     {
+        if (isEmpty())
+            return x;
         x = std::clamp(x, 0.0f, 1.0f);
         x *= m_tableSize - 1;
         const uint32_t lo = static_cast<uint32_t>(std::floor(x));
         const uint32_t hi = std::min(lo + 1, m_tableSize - 1);
         const float frac = x - lo;
         if (!m_table16.isEmpty())
-            return (m_table16[lo] * (1.0f - frac) + m_table16[hi] * frac) * (1.0f/65535.0f);
+            return (m_table16[lo] + (m_table16[hi] - m_table16[lo]) * frac) * (1.0f/65535.0f);
         if (!m_table8.isEmpty())
-            return (m_table8[lo] * (1.0f - frac) + m_table8[hi] * frac) * (1.0f/255.0f);
+            return (m_table8[lo] + (m_table8[hi] - m_table8[lo]) * frac) * (1.0f/255.0f);
         return x;
     }
 
@@ -96,6 +115,7 @@ public:
     float applyInverse(float x, float resultLargerThan = 0.0f) const
     {
         Q_ASSERT(resultLargerThan >= 0.0f && resultLargerThan <= 1.0f);
+        Q_ASSERT(m_type == TwoWay);
         if (x <= 0.0f)
             return 0.0f;
         if (x >= 1.0f)
@@ -105,6 +125,8 @@ public:
             uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1)));
             auto it = std::lower_bound(m_table16.cbegin() + i, m_table16.cend(), v);
             i = it - m_table16.cbegin();
+            if (i == 0)
+                return 0.0f;
             if (i >= m_tableSize - 1)
                 return 1.0f;
             const float y1 = m_table16[i - 1];
@@ -112,13 +134,14 @@ public:
             Q_ASSERT(v >= y1 && v <= y2);
             const float fr = (v - y1) / (y2 - y1);
             return (i + fr) * (1.0f / (m_tableSize - 1));
-
         }
         if (!m_table8.isEmpty()) {
             const float v = x * 255.0f;
             uint32_t i = static_cast<uint32_t>(std::floor(resultLargerThan * (m_tableSize - 1)));
             auto it = std::lower_bound(m_table8.cbegin() + i, m_table8.cend(), v);
             i = it - m_table8.cbegin();
+            if (i == 0)
+                return 0.0f;
             if (i >= m_tableSize - 1)
                 return 1.0f;
             const float y1 = m_table8[i - 1];
@@ -133,6 +156,10 @@ public:
     bool asColorTransferFunction(QColorTransferFunction *transferFn)
     {
         Q_ASSERT(transferFn);
+        if (isEmpty()) {
+            *transferFn = QColorTransferFunction();
+            return true;
+        }
         if (m_tableSize < 2)
             return false;
         if (!m_table8.isEmpty() && (m_table8[0] != 0 || m_table8[m_tableSize - 1] != 255))
@@ -182,7 +209,8 @@ public:
     friend inline bool operator!=(const QColorTransferTable &t1, const QColorTransferTable &t2);
     friend inline bool operator==(const QColorTransferTable &t1, const QColorTransferTable &t2);
 
-    uint32_t m_tableSize;
+    Type m_type = TwoWay;
+    uint32_t m_tableSize = 0;
     QList<uint8_t> m_table8;
     QList<uint16_t> m_table16;
 };
@@ -191,6 +219,8 @@ inline bool operator!=(const QColorTransferTable &t1, const QColorTransferTable
 {
     if (t1.m_tableSize != t2.m_tableSize)
         return true;
+    if (t1.m_type != t2.m_type)
+        return true;
     if (t1.m_table8.isEmpty() != t2.m_table8.isEmpty())
         return true;
     if (t1.m_table16.isEmpty() != t2.m_table16.isEmpty())