Add demo of the new QGradient presets to the gradients example

In the gradients example, allow the user to select and show
QGradient's named presets.

Change-Id: I40bc6cbe3a0316ce49d67d63511881b6f6112574
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

examples/widgets/doc/src/gradients.qdoc

@@ -51,7 +51,12 @@
     gradient. You can move points, and add new ones, by clicking with the left
     mouse button, and remove points by clicking with the right button.
 
-    There are three default configurations available at the bottom of
+    There are three example configurations available at the bottom of
     the page that are provided as suggestions on how a color table could be
     configured.
+
+    Qt also provides a suite of named gradient presets. They are based on the
+    free WebGradients collection. Click on the name in the Presets box to show
+    the gradient. Use the arrow buttons to browse through the available
+    presets.
 */

examples/widgets/painting/gradients/gradients.cpp

@@ -301,8 +301,15 @@ GradientWidget::GradientWidget(QWidget *parent)
     m_reflectSpreadButton = new QRadioButton(tr("Reflect Spread"), spreadGroup);
     m_repeatSpreadButton = new QRadioButton(tr("Repeat Spread"), spreadGroup);
 
+    QGroupBox *presetsGroup = new QGroupBox(mainGroup);
+    presetsGroup->setTitle(tr("Presets"));
+    QPushButton *prevPresetButton = new QPushButton(tr("<"), presetsGroup);
+    m_presetButton = new QPushButton(tr("(unset)"), presetsGroup);
+    QPushButton *nextPresetButton = new QPushButton(tr(">"), presetsGroup);
+    updatePresetName();
+
     QGroupBox *defaultsGroup = new QGroupBox(mainGroup);
-    defaultsGroup->setTitle(tr("Defaults"));
+    defaultsGroup->setTitle(tr("Examples"));
     QPushButton *default1Button = new QPushButton(tr("1"), defaultsGroup);
     QPushButton *default2Button = new QPushButton(tr("2"), defaultsGroup);
     QPushButton *default3Button = new QPushButton(tr("3"), defaultsGroup);
@@ -327,11 +334,12 @@ GradientWidget::GradientWidget(QWidget *parent)
     mainLayout->addWidget(m_renderer);
     mainLayout->addWidget(mainGroup);
 
-    mainGroup->setFixedWidth(180);
+    mainGroup->setFixedWidth(200);
     QVBoxLayout *mainGroupLayout = new QVBoxLayout(mainGroup);
     mainGroupLayout->addWidget(editorGroup);
     mainGroupLayout->addWidget(typeGroup);
     mainGroupLayout->addWidget(spreadGroup);
+    mainGroupLayout->addWidget(presetsGroup);
     mainGroupLayout->addWidget(defaultsGroup);
     mainGroupLayout->addStretch(1);
     mainGroupLayout->addWidget(showSourceButton);
@@ -353,6 +361,11 @@ GradientWidget::GradientWidget(QWidget *parent)
     spreadGroupLayout->addWidget(m_repeatSpreadButton);
     spreadGroupLayout->addWidget(m_reflectSpreadButton);
 
+    QHBoxLayout *presetsGroupLayout = new QHBoxLayout(presetsGroup);
+    presetsGroupLayout->addWidget(prevPresetButton);
+    presetsGroupLayout->addWidget(m_presetButton, 1);
+    presetsGroupLayout->addWidget(nextPresetButton);
+
     QHBoxLayout *defaultsGroupLayout = new QHBoxLayout(defaultsGroup);
     defaultsGroupLayout->addWidget(default1Button);
     defaultsGroupLayout->addWidget(default2Button);
@@ -375,6 +388,13 @@ GradientWidget::GradientWidget(QWidget *parent)
     connect(m_repeatSpreadButton, &QRadioButton::clicked,
             m_renderer, &GradientRenderer::setRepeatSpread);
 
+    connect(prevPresetButton, &QPushButton::clicked,
+            this, &GradientWidget::setPrevPreset);
+    connect(m_presetButton, &QPushButton::clicked,
+            this, &GradientWidget::setPreset);
+    connect(nextPresetButton, &QPushButton::clicked,
+            this, &GradientWidget::setNextPreset);
+
     connect(default1Button, &QPushButton::clicked,
             this, &GradientWidget::setDefault1);
     connect(default2Button, &QPushButton::clicked,
@@ -471,6 +491,40 @@ void GradientWidget::setDefault(int config)
     m_renderer->setGradientStops(stops);
 }
 
+void GradientWidget::updatePresetName()
+{
+    QMetaEnum presetEnum = QMetaEnum::fromType<QGradient::Preset>();
+    m_presetButton->setText(QLatin1String(presetEnum.key(m_presetIndex)));
+}
+
+void GradientWidget::changePresetBy(int indexOffset)
+{
+    QMetaEnum presetEnum = QMetaEnum::fromType<QGradient::Preset>();
+    m_presetIndex = qBound(0, m_presetIndex + indexOffset, presetEnum.keyCount() - 1);
+
+    QGradient::Preset preset = static_cast<QGradient::Preset>(presetEnum.value(m_presetIndex));
+    QGradient gradient(preset);
+    if (gradient.type() != QGradient::LinearGradient)
+        return;
+
+    QLinearGradient *linearGradientPointer = static_cast<QLinearGradient *>(&gradient);
+    QLineF objectStopsLine(linearGradientPointer->start(), linearGradientPointer->finalStop());
+    qreal scaleX = qFuzzyIsNull(objectStopsLine.dx()) ? 1.0 : (0.8 * m_renderer->width() / qAbs(objectStopsLine.dx()));
+    qreal scaleY = qFuzzyIsNull(objectStopsLine.dy()) ? 1.0 : (0.8 * m_renderer->height() / qAbs(objectStopsLine.dy()));
+    QLineF logicalStopsLine = QTransform::fromScale(scaleX, scaleY).map(objectStopsLine);
+    logicalStopsLine.translate(m_renderer->rect().center() - logicalStopsLine.center());
+    QPolygonF logicalStops;
+    logicalStops << logicalStopsLine.p1() << logicalStopsLine.p2();
+
+    m_linearButton->animateClick();
+    m_padSpreadButton->animateClick();
+    m_editor->setGradientStops(gradient.stops());
+    m_renderer->hoverPoints()->setPoints(logicalStops);
+    m_renderer->setGradientStops(gradient.stops());
+
+    updatePresetName();
+}
+
 GradientRenderer::GradientRenderer(QWidget *parent)
     : ArthurFrame(parent)
 {

examples/widgets/painting/gradients/gradients.h

@@ -164,9 +164,14 @@ public slots:
     void setDefault2() { setDefault(2); }
     void setDefault3() { setDefault(3); }
     void setDefault4() { setDefault(4); }
+    void setPreset()     { changePresetBy(0); }
+    void setPrevPreset() { changePresetBy(-1); }
+    void setNextPreset() { changePresetBy(1); }
 
 private:
     void setDefault(int i);
+    void updatePresetName();
+    void changePresetBy(int indexOffset);
 
     GradientRenderer *m_renderer;
     GradientEditor *m_editor;
@@ -177,7 +182,9 @@ private:
     QRadioButton *m_padSpreadButton;
     QRadioButton *m_reflectSpreadButton;
     QRadioButton *m_repeatSpreadButton;
+    QPushButton *m_presetButton;
 
+    int m_presetIndex = 0;
 };
 
 #endif // GRADIENTS_H

examples/widgets/painting/gradients/gradients.html

@@ -24,8 +24,12 @@ green and blue components while the last defines the alpha of the
 gradient. You can move points, and add new ones, by clicking with the left
 mouse button, and remove points by clicking with the right button.</p>
 
-<p>There are three default configurations available at the bottom of
+<p>There are three example configurations available at the bottom of
 the page that are provided as suggestions on how a color table could be
 configured.</p>
 
+<p>Qt also provides a suite of named gradient presets. They are based on the
+free WebGradients collection. Click on the name in the Presets box to show the
+gradient. Use the arrow buttons to browse through the available presets.</p>
+
 </html>