Création de la configuration et des paramètres par défaut

etc/adminhtml/system.xml

+<?xml version="1.0"?>
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
+    <system>
+        <section id="categorywidget" translate="label" sortOrder="15" showInDefault="1" showInWebsite="1" showInStore="1">
+            <class>separator-top</class>
+            <label>Image Slider Manager</label>
+            <tab>nicolasbejean</tab>
+            <resource>NicolasBejean_CategoryWidget::global</resource>
+            <group id="resize" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
+                <label>Image Resize Settings</label>
+                <comment>Default Resize Settings</comment>
+                <field id="constrain_only" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Constrain Only</label>
+                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
+                    <comment>Guarantee, that image picture will not be bigger, than it was. It is false by default.</comment>
+                </field>
+                <field id="keep_aspect_ratio" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Keep Aspect Ratio</label>
+                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
+                    <comment>Guarantee, that image picture width/height will not be distorted. It is true by default.</comment>
+                </field>
+                <field id="keep_transparency" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Keep Transparency</label>
+                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
+                    <comment>Guarantee, that image will not lose transparency if any. It is true by default.</comment>
+                </field>
+                <field id="keep_frame" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Keep Frame</label>
+                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
+                    <comment>Guarantee, that image will have dimensions, set in $width/$height. Not applicable, if keepAspectRatio(false).</comment>
+                </field>
+                <field id="background_color" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Background Color</label>
+                    <comment>Default white</comment>
+                </field>
+            </group>
+            <group id="save" translate="label" type="text" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="1">
+                <label>Image Saved Settings</label>
+                <comment>Default Save Settings</comment>
+                <field id="identifier" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Identifier</label>
+                </field>
+                <field id="basename" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Basename</label>
+                </field>
+                <field id="width" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Width</label>
+                </field>
+                <field id="height" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Height</label>
+                </field>
+                <field id="compression" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
+                    <label>Compression</label>
+                </field>
+            </group>
+        </section>
+    </system>
+</config>

etc/config.xml

+<?xml version="1.0"?>
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
+    <default>
+        <categorywidget>
+            <resize>
+                <constrain_only>0</constrain_only>
+                <keep_aspect_ratio>1</keep_aspect_ratio>
+                <keep_transparency>1</keep_transparency>
+                <keep_frame>1</keep_frame>
+                <background_color>#ffffff</background_color>
+            </resize>
+            <save>
+                <identifier>cw</identifier>
+                <basename></basename>
+                <width>1920</width>
+                <height>1080</height>
+                <compression>60</compression>
+            </save>
+        </categorywidget>
+    </default>
+</config>