Twig/UiExtension.php
public function renderButton($label = '', array $options = [], array $attributes = [])
    {
        $options = $this->getButtonOptionsResolver()->resolve($options);

        $tag = 'button';
        $classes = ['btn', 'btn-'.$options['theme'], 'btn-'.$options['size']];
        $defaultAttributes = [
        	'class' => sprintf('btn btn-%s btn-%s', $options['theme'], $options['size']),
        ];
        if ($options['type'] == 'link') {
            if (0 == strlen($options['path'])) {
                throw new \InvalidArgumentException('"path" option must be defined for "link" button type.');
            }
            $tag = 'a';
            $defaultAttributes['href'] = $options['path'];
        } else {
            $defaultAttributes['type'] = $options['type'];
        }

        if (array_key_exists('class', $attributes)) {
            $classes = array_merge($classes, explode(' ', $attributes['class']));
            unset($attributes['class']);
        }
        $defaultAttributes['class'] = implode(' ', $classes);
        $attributes = array_merge($defaultAttributes, $attributes);

        $icon = '';
        if(0 < strlen($options['icon'])) {
            $icon = $options['fa_icon'] ? 'fa fa-'.$options['icon'] : 'glyphicon glyphicon-'.$options['icon'];
        }

        return $this->controlsTemplate->renderBlock('button', [
            'tag'   => $tag,
            'attr'  => $attributes,
            'label' => $label,
            'icon'  => $icon,
        ]);
    }
public function renderButton($label = '', array $options = [], array $attributes = [])
    {
        $options = $this->getButtonOptionsResolver()->resolve($options);

        $tag = 'button';
        $classes = ['btn', 'btn-'.$options['theme'], 'btn-'.$options['size']];
        $defaultAttributes = [
        	'class' => sprintf('btn btn-%s btn-%s', $options['theme'], $options['size']),
        ];
        if ($options['type'] == 'link') {
            if (0 == strlen($options['path'])) {
                throw new \InvalidArgumentException('"path" option must be defined for "link" button type.');
            }
            $tag = 'a';
            $defaultAttributes['href'] = $options['path'];
        } else {
            $defaultAttributes['type'] = $options['type'];
        }

        if (array_key_exists('class', $attributes)) {
            $classes = array_merge($classes, explode(' ', $attributes['class']));
            unset($attributes['class']);
        }
        $defaultAttributes['class'] = implode(' ', $classes);
        $attributes = array_merge($defaultAttributes, $attributes);

        $icon = '';
        if(0 < strlen($options['icon'])) {
            $icon = $options['fa_icon'] ? 'fa fa-'.$options['icon'] : 'glyphicon glyphicon-'.$options['icon'];
        }

        return $this->controlsTemplate->renderBlock('button', [
            'tag'   => $tag,
            'attr'  => $attributes,
            'label' => $label,
            'icon'  => $icon,
        ]);
    }
Renders the button.

@param string $label
@param array $options
@param array $attributes
@return string
@throws \InvalidArgumentException