Make scrollbar mouse interaction similar to modern OS behavior

include/ui/ScrollBar.hpp

@@ -17,6 +17,7 @@ struct ScrollBar : widget::OpaqueWidget {
 	ScrollBar();
 	~ScrollBar();
 	void draw(const DrawArgs& args) override;
+	void onButton(const event::Button& e) override;
 	void onDragStart(const event::DragStart& e) override;
 	void onDragEnd(const event::DragEnd& e) override;
 	void onDragMove(const event::DragMove& e) override;

include/ui/ScrollWidget.hpp

@@ -22,6 +22,12 @@ struct ScrollWidget : widget::OpaqueWidget {
 
 	ScrollWidget();
 	void scrollTo(math::Rect r);
+	/** Returns the bound of allowed `offset` values in pixels. */
+	math::Rect getContainerOffsetBound();
+	/** Returns the handle position relative to the scrollbar. [0, 1]. */
+	math::Vec getHandleOffset();
+	/** Returns the handle size relative to the scrollbar. [0, 1]. */
+	math::Vec getHandleSize();
 	void draw(const DrawArgs& args) override;
 	void step() override;
 	void onButton(const event::Button& e) override;

src/ui/ScrollBar.cpp

@@ -30,26 +30,40 @@ void ScrollBar::draw(const DrawArgs& args) {
 	if (APP->event->getDraggedWidget() == this)
 		state = BND_ACTIVE;
 
-	float offsetBound = sw->containerBox.size.get(vertical) - sw->box.size.get(vertical);
-	// The handle position relative to the scrollbar. [0, 1]
-	float scrollBarOffset = (sw->offset.get(vertical) - sw->containerBox.pos.get(vertical)) / offsetBound;
-	// The handle size relative to the scrollbar. [0, 1]
-	float scrollBarSize = sw->box.size.get(vertical) / sw->containerBox.size.get(vertical);
-	bndScrollBar(args.vg, 0.0, 0.0, box.size.x, box.size.y, state, scrollBarOffset, scrollBarSize);
+	float handleOffset = sw->getHandleOffset().get(vertical);
+	float handleSize = sw->getHandleSize().get(vertical);
+	bndScrollBar(args.vg, 0.0, 0.0, box.size.x, box.size.y, state, handleOffset, handleSize);
 }
 
 
-void ScrollBar::onDragStart(const event::DragStart& e) {
-	if (e.button == GLFW_MOUSE_BUTTON_LEFT) {
-		APP->window->cursorLock();
+void ScrollBar::onButton(const event::Button& e) {
+	if (e.button == GLFW_MOUSE_BUTTON_LEFT && e.action == GLFW_PRESS) {
+		ScrollWidget* sw = dynamic_cast<ScrollWidget*>(parent);
+		assert(sw);
+
+		float pos = e.pos.get(vertical);
+		pos /= box.size.get(vertical);
+		float handleOffset = sw->getHandleOffset().get(vertical);
+		float handleSize = sw->getHandleSize().get(vertical);
+		float handlePos = math::rescale(handleOffset, 0.f, 1.f, handleSize / 2.f, 1.f - handleSize / 2.f);
+		math::Rect offsetBound = sw->getContainerOffsetBound();
+
+		// Check if user clicked on handle
+		if (std::fabs(pos - handlePos) > handleSize / 2.f) {
+			// Jump to absolute position of the handle
+			float offset = math::rescale(pos, handleSize / 2.f, 1.f - handleSize / 2.f, 0.f, 1.f);
+			sw->offset.get(vertical) = sw->containerBox.pos.get(vertical) + offset * (sw->containerBox.size.get(vertical) - sw->box.size.get(vertical));
+		}
 	}
+	OpaqueWidget::onButton(e);
+}
+
+
+void ScrollBar::onDragStart(const event::DragStart& e) {
 }
 
 
 void ScrollBar::onDragEnd(const event::DragEnd& e) {
-	if (e.button == GLFW_MOUSE_BUTTON_LEFT) {
-		APP->window->cursorUnlock();
-	}
 }
 
 
@@ -57,13 +71,14 @@ void ScrollBar::onDragMove(const event::DragMove& e) {
 	ScrollWidget* sw = dynamic_cast<ScrollWidget*>(parent);
 	assert(sw);
 
-	// TODO
-	// float offsetBound = sw->containerBox.size.get(vertical) - sw->box.size.get(vertical);
-	// float scrollBarSize = sw->box.size.get(vertical) / sw->containerBox.size.get(vertical);
+	// Move handle absolutely.
+	float mouseDelta = e.mouseDelta.get(vertical);
+	mouseDelta /= getAbsoluteZoom();
 
-	const float sensitivity = 1.f;
-	float offsetDelta = e.mouseDelta.get(vertical);
-	offsetDelta *= sensitivity;
+	float handleSize = sw->getHandleSize().get(vertical);
+	float handleBound = (1.f - handleSize) * box.size.get(vertical);
+	float offsetBound = sw->getContainerOffsetBound().size.get(vertical);
+	float offsetDelta = mouseDelta * offsetBound / handleBound;
 	sw->offset.get(vertical) += offsetDelta;
 }
 

src/ui/ScrollWidget.cpp

@@ -31,6 +31,24 @@ void ScrollWidget::scrollTo(math::Rect r) {
 }
 
 
+math::Rect ScrollWidget::getContainerOffsetBound() {
+	math::Rect r;
+	r.pos = containerBox.pos;
+	r.size = containerBox.size.minus(box.size);
+	return r;
+}
+
+
+math::Vec ScrollWidget::getHandleOffset() {
+	return offset.minus(containerBox.pos).div(getContainerOffsetBound().size);
+}
+
+
+math::Vec ScrollWidget::getHandleSize() {
+	return box.size.div(containerBox.size);
+}
+
+
 void ScrollWidget::draw(const DrawArgs& args) {
 	nvgScissor(args.vg, RECT_ARGS(args.clipBox));
 	Widget::draw(args);
@@ -41,10 +59,11 @@ void ScrollWidget::draw(const DrawArgs& args) {
 void ScrollWidget::step() {
 	Widget::step();
 
-	// Clamp scroll offset
+	// Set containerBox cache
 	containerBox = container->getChildrenBoundingBox();
-	math::Rect offsetBounds = containerBox;
-	offsetBounds.size = offsetBounds.size.minus(box.size);
+
+	// Clamp scroll offset
+	math::Rect offsetBounds = getContainerOffsetBound();
 	offset = offset.clamp(offsetBounds);
 
 	// Update the container's position from the offset
@@ -69,7 +88,7 @@ void ScrollWidget::onButton(const event::Button& e) {
 		return;
 
 	// Consume right button only if the scrollbars are visible
-	if (!(horizontalScrollBar->visible || verticalScrollBar->visible))
+	if (!(horizontalScrollBar->isVisible() || verticalScrollBar->isVisible()))
 		return;
 
 	if (e.button == GLFW_MOUSE_BUTTON_MIDDLE) {
@@ -87,7 +106,7 @@ void ScrollWidget::onDragStart(const event::DragStart& e) {
 
 void ScrollWidget::onDragMove(const event::DragMove& e) {
 	// Scroll only if the scrollbars are visible
-	if (!(horizontalScrollBar->visible || verticalScrollBar->visible))
+	if (!(horizontalScrollBar->isVisible() || verticalScrollBar->isVisible()))
 		return;
 
 	offset = offset.minus(e.mouseDelta);
@@ -100,7 +119,7 @@ void ScrollWidget::onHoverScroll(const event::HoverScroll& e) {
 		return;
 
 	// Scroll only if the scrollbars are visible
-	if (!(horizontalScrollBar->visible || verticalScrollBar->visible))
+	if (!(horizontalScrollBar->isVisible() || verticalScrollBar->isVisible()))
 		return;
 
 	math::Vec scrollDelta = e.scrollDelta;