Fix a crash when SVG filters fail

This bug was triggered by a test in the resvg test suit:
filters/filters/in=BackgroundAlpha.svg

The patch further includes a small optimization: The sourceAlpha
filter buffer is only created on request.

Pick-to: 6.7
Change-Id: I208d43c54f07d530f476b459f30c1b8aa62c2018
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

4 files changed, 72 insertions, 15 deletions

diff --git a/src/svg/qsvgfilter.cpp b/src/svg/qsvgfilter.cpp
index 2c86f7d..59d928d 100644
--- a/src/svg/qsvgfilter.cpp
+++ b/src/svg/qsvgfilter.cpp
@@ -61,6 +61,25 @@ void QSvgFeFilterPrimitive::clipToTransformedBounds(QImage *buffer, QPainter *p,
     painter.fillPath(clipPath, Qt::transparent);
 }
 
+bool QSvgFeFilterPrimitive::requiresSourceAlpha() const
+{
+    return m_input == QLatin1StringView("SourceAlpha");
+}
+
+const QSvgFeFilterPrimitive *QSvgFeFilterPrimitive::castToFilterPrimitive(const QSvgNode *node)
+{
+    if (node->type() == QSvgNode::FeMerge ||
+        node->type() == QSvgNode::FeColormatrix ||
+        node->type() == QSvgNode::FeGaussianblur ||
+        node->type() == QSvgNode::FeOffset ||
+        node->type() == QSvgNode::FeComposite ||
+        node->type() == QSvgNode::FeFlood ) {
+        return reinterpret_cast<const QSvgFeFilterPrimitive*>(node);
+    } else {
+        return nullptr;
+    }
+}
+
 QSvgFeColorMatrix::QSvgFeColorMatrix(QSvgNode *parent, QString input, QString result, const QSvgRectF &rect,
                                      ColorShiftType type, Matrix matrix)
     : QSvgFeFilterPrimitive(parent, input, result, rect)
@@ -449,6 +468,19 @@ QImage QSvgFeMerge::apply(QSvgNode *item, const QMap<QString, QImage> &sources,
     return result;
 }
 
+bool QSvgFeMerge::requiresSourceAlpha() const
+{
+    for (int i = 0; i < renderers().size(); i++) {
+        QSvgNode *child = renderers().at(i);
+        if (child->type() == QSvgNode::FeMergenode) {
+            QSvgFeMergeNode *filter = static_cast<QSvgFeMergeNode *>(child);
+            if (filter->requiresSourceAlpha())
+                return true;
+        }
+    }
+    return false;
+}
+
 QSvgFeMergeNode::QSvgFeMergeNode(QSvgNode *parent, QString input, QString result, const QSvgRectF &rect)
     : QSvgFeFilterPrimitive(parent, input, result, rect)
 {
@@ -601,6 +633,14 @@ QImage QSvgFeComposite::apply(QSvgNode *item, const QMap<QString, QImage> &sourc
     return result;
 }
 
+bool QSvgFeComposite::requiresSourceAlpha() const
+{
+    if (QSvgFeFilterPrimitive::requiresSourceAlpha())
+        return true;
+    return m_input2 == QLatin1StringView("SourceAlpha");
+}
+
+
 QSvgFeFlood::QSvgFeFlood(QSvgNode *parent, QString input, QString result,
                          const QSvgRectF &rect, const QColor &color)
     : QSvgFeFilterPrimitive(parent, input, result, rect)
diff --git a/src/svg/qsvgfilter_p.h b/src/svg/qsvgfilter_p.h
index baeb0dc..22ecc59 100644
--- a/src/svg/qsvgfilter_p.h
+++ b/src/svg/qsvgfilter_p.h
@@ -43,12 +43,16 @@ public:
     virtual QImage apply(QSvgNode *item, const QMap<QString, QImage> &sources,
                          QPainter *p, const QRectF &itemBounds, const QRectF &filterBounds,
                          QSvg::UnitTypes primitiveUnits, QSvg::UnitTypes filterUnits) const = 0;
+    virtual bool requiresSourceAlpha() const;
     QString input() const {
         return m_input;
     }
     QString result() const {
         return m_result;
     }
+
+    static const QSvgFeFilterPrimitive *castToFilterPrimitive(const QSvgNode *node);
+
 protected:
     QString m_input;
     QString m_result;
@@ -124,6 +128,7 @@ public:
     QImage apply(QSvgNode *item, const QMap<QString, QImage> &sources,
                  QPainter *p, const QRectF &itemBounds, const QRectF &filterBounds,
                  QSvg::UnitTypes primitiveUnits, QSvg::UnitTypes filterUnits) const override;
+    bool requiresSourceAlpha() const override;
 };
 
 class Q_SVG_EXPORT QSvgFeMergeNode : public QSvgFeFilterPrimitive
@@ -154,6 +159,7 @@ public:
     QImage apply(QSvgNode *item, const QMap<QString, QImage> &sources,
                  QPainter *p, const QRectF &itemBounds, const QRectF &filterBounds,
                  QSvg::UnitTypes primitiveUnits, QSvg::UnitTypes filterUnits) const override;
+    bool requiresSourceAlpha() const override;
 private:
     QString m_input2;
     Operator m_operator;
diff --git a/src/svg/qsvgstructure.cpp b/src/svg/qsvgstructure.cpp
index 9234fe5..1cfd441 100644
--- a/src/svg/qsvgstructure.cpp
+++ b/src/svg/qsvgstructure.cpp
@@ -387,28 +387,38 @@ QImage QSvgFilterContainer::applyFilter(QSvgNode *item, const QImage &buffer, QP
 
     QImage proxy = buffer.copy(filterBoundsGlobRel);
     proxy.setOffset(filterBoundsGlob.topLeft());
-
-    QImage proxyAlpha = proxy.convertedTo(QImage::Format_Alpha8).convertedTo(proxy.format());
-    // ### TODO: allocation check
-    proxyAlpha.setOffset(proxy.offset());
+    if (proxy.isNull())
+        return buffer;
 
     QMap<QString, QImage> buffers;
     buffers[QStringLiteral("")] = proxy;
     buffers[QStringLiteral("SourceGraphic")] = proxy;
-    buffers[QStringLiteral("SourceAlpha")] = proxyAlpha;
+
+    bool requiresSourceAlpha = false;
+
+    const QList<QSvgNode *> children = renderers();
+    for (const QSvgNode *renderer : children) {
+        const QSvgFeFilterPrimitive *filter = QSvgFeFilterPrimitive::castToFilterPrimitive(renderer);
+        if (filter && filter->requiresSourceAlpha()) {
+            requiresSourceAlpha = true;
+            break;
+        }
+    }
+
+    if (requiresSourceAlpha) {
+        QImage proxyAlpha = proxy.convertedTo(QImage::Format_Alpha8).convertedTo(proxy.format());
+        proxyAlpha.setOffset(proxy.offset());
+        if (proxyAlpha.isNull())
+            return buffer;
+        buffers[QStringLiteral("SourceAlpha")] = proxyAlpha;
+    }
 
     QImage result;
-    for (int i = 0; i < renderers().size(); i++) {
-        QSvgNode *child = renderers().at(i);
-        if (child->type() == QSvgNode::FeMerge ||
-            child->type() == QSvgNode::FeColormatrix ||
-            child->type() == QSvgNode::FeGaussianblur ||
-            child->type() == QSvgNode::FeOffset ||
-            child->type() == QSvgNode::FeComposite ||
-            child->type() == QSvgNode::FeFlood ) {
-            QSvgFeFilterPrimitive *filter = reinterpret_cast<QSvgFeFilterPrimitive*>(child);
+    for (const QSvgNode *renderer : children) {
+        const QSvgFeFilterPrimitive *filter = QSvgFeFilterPrimitive::castToFilterPrimitive(renderer);
+        if (filter) {
             result = filter->apply(item, buffers, p, bounds, filterBounds, m_primitiveUnits, m_filterUnits);
-            if (result.size().isValid()) {
+            if (!result.isNull()) {
                 buffers[QStringLiteral("")] = result;
                 buffers[filter->result()] = result;
             }
diff --git a/src/svg/qsvgtinydocument_p.h b/src/svg/qsvgtinydocument_p.h
index d0b1dbb..b6780ae 100644
--- a/src/svg/qsvgtinydocument_p.h
+++ b/src/svg/qsvgtinydocument_p.h
@@ -86,6 +86,7 @@ public:
     int currentFrame() const;
     void setCurrentFrame(int);
     void setFramesPerSecond(int num);
+
 private:
     void mapSourceToTarget(QPainter *p, const QRectF &targetRect, const QRectF &sourceRect = QRectF());
 private: