Effects manifest defaults

src/effects/presets/effectpreset.cpp

@@ -1,5 +1,8 @@
 #include "effects/presets/effectpreset.h"
 
+#include <QHash>
+#include <functional>
+
 #include "effects/backends/effectsbackend.h"
 #include "effects/effectslot.h"
 #include "effects/presets/effectxmlelements.h"
@@ -99,5 +102,28 @@ const QDomElement EffectPreset::toXml(QDomDocument* doc) const {
     return effectElement;
 }
 
-EffectPreset::~EffectPreset() {
+void EffectPreset::updateParametersFrom(const EffectPreset& other) {
+    DEBUG_ASSERT(backendType() == other.backendType());
+
+    // we use a std::reference_wrapper as optimization so we don't copy and
+    // store the entire object when we need to copy later anyways
+    // TODO(XXX): Replace QHash with <std::flat_map>
+    QHash<QString, std::reference_wrapper<const EffectParameterPreset>> parameterPresetLookup;
+    // we build temporary hashtable to reduce the algorithmic complexity of the
+    // lookup later. A plain std::find_if (O(n)) would've resulted in O(n^n)
+    // parameter updating. The hashtable has O(1) lookup with O(n) updating,
+    // though with more constant overhead. Since 3rd-party EffectPresets could
+    // have hundreds of parameters, we can't afford O(n^2) lookups.
+    // TODO(XXX): measure overhead and possibly implement fallback to lower
+    // overhead O(n^2) solution for small presets.
+    for (const EffectParameterPreset& preset : other.m_effectParameterPresets) {
+        parameterPresetLookup.insert(preset.id(), std::ref(preset));
+    }
+
+    for (EffectParameterPreset& parameterToUpdate : m_effectParameterPresets) {
+        const auto parameterToCopyIt = parameterPresetLookup.constFind(parameterToUpdate.id());
+        if (parameterToCopyIt != parameterPresetLookup.constEnd()) {
+            parameterToUpdate = *parameterToCopyIt;
+        }
+    }
 }

src/effects/presets/effectpreset.h

@@ -15,7 +15,6 @@ class EffectPreset {
     EffectPreset(const QDomElement& element);
     EffectPreset(const EffectSlotPointer pEffectSlot);
     EffectPreset(const EffectManifestPointer pManifest);
-    ~EffectPreset();
 
     const QDomElement toXml(QDomDocument* doc) const;
 
@@ -39,6 +38,15 @@ class EffectPreset {
         return m_effectParameterPresets;
     }
 
+    /// updates all of the parameters of `this` with the parameters
+    /// of `preset`.
+    /// The operation is not symmetric:
+    /// Parameters which are present on `preset` but not on `this` will
+    /// not be added to `this`
+    /// Parameters present on `this` but not `preset` will keep their previous
+    /// settings
+    void updateParametersFrom(const EffectPreset& preset);
+
   private:
     QString m_id;
     EffectBackendType m_backendType;

src/effects/presets/effectpresetmanager.cpp

@@ -39,11 +39,13 @@ void EffectPresetManager::loadDefaultEffectPresets() {
             file.close();
             continue;
         }
-        EffectPresetPointer pEffectPreset(new EffectPreset(doc.documentElement()));
-        if (!pEffectPreset->isEmpty()) {
+        auto presetFromFile = EffectPreset(doc.documentElement());
+        if (!presetFromFile.isEmpty()) {
             EffectManifestPointer pManifest = m_pBackendManager->getManifest(
-                    pEffectPreset->id(), pEffectPreset->backendType());
+                    presetFromFile.id(), presetFromFile.backendType());
             if (pManifest) {
+                auto pEffectPreset = EffectPresetPointer(new EffectPreset(pManifest));
+                pEffectPreset->updateParametersFrom(presetFromFile);
                 m_defaultPresets.insert(pManifest, pEffectPreset);
             }
         }