Smooth scrolling (minetest#14562)

src/gui/guiEditBox.cpp

@@ -774,9 +774,9 @@ bool GUIEditBox::processMouse(const SEvent &event)
  }
  case EMIE_MOUSE_WHEEL:
  if (m_vscrollbar && m_vscrollbar->isVisible()) {
- s32 pos = m_vscrollbar->getPos();
+ s32 pos = m_vscrollbar->getTargetPos();
  s32 step = m_vscrollbar->getSmallStep();
- m_vscrollbar->setPos(pos - event.MouseInput.Wheel * step);
+ m_vscrollbar->setPosInterpolated(pos - event.MouseInput.Wheel * step);
  return true;
  }
  break;

src/gui/guiHyperText.cpp

@@ -1084,7 +1084,7 @@ bool GUIHyperText::OnEvent(const SEvent &event)
  checkHover(event.MouseInput.X, event.MouseInput.Y);
 
  if (event.MouseInput.Event == EMIE_MOUSE_WHEEL && m_vscrollbar->isVisible()) {
- m_vscrollbar->setPos(m_vscrollbar->getPos() -
+ m_vscrollbar->setPosInterpolated(m_vscrollbar->getTargetPos() -
  event.MouseInput.Wheel * m_vscrollbar->getSmallStep());
  m_text_scrollpos.Y = -m_vscrollbar->getPos();
  m_drawer.draw(m_display_text_rect, m_text_scrollpos);

src/gui/guiScrollBar.cpp

@@ -12,6 +12,7 @@ the arrow buttons where there is insufficient space.
 
 #include "guiScrollBar.h"
 #include "guiButton.h"
+#include "porting.h"
 #include <IGUISkin.h>
 
 GUIScrollBar::GUIScrollBar(IGUIEnvironment *environment, IGUIElement *parent, s32 id,
@@ -38,57 +39,42 @@ bool GUIScrollBar::OnEvent(const SEvent &event)
  switch (event.EventType) {
  case EET_KEY_INPUT_EVENT:
  if (event.KeyInput.PressedDown) {
- const s32 old_pos = scroll_pos;
+ const s32 old_pos = getTargetPos();
  bool absorb = true;
  switch (event.KeyInput.Key) {
  case KEY_LEFT:
  case KEY_UP:
- setPos(scroll_pos - small_step);
+ setPosInterpolated(old_pos - small_step);
  break;
  case KEY_RIGHT:
  case KEY_DOWN:
- setPos(scroll_pos + small_step);
+ setPosInterpolated(old_pos + small_step);
  break;
  case KEY_HOME:
- setPos(min_pos);
+ setPosInterpolated(min_pos);
  break;
  case KEY_PRIOR:
- setPos(scroll_pos - large_step);
+ setPosInterpolated(old_pos - large_step);
  break;
  case KEY_END:
- setPos(max_pos);
+ setPosInterpolated(max_pos);
  break;
  case KEY_NEXT:
- setPos(scroll_pos + large_step);
+ setPosInterpolated(old_pos + large_step);
  break;
  default:
  absorb = false;
  }
- if (scroll_pos != old_pos) {
- SEvent e;
- e.EventType = EET_GUI_EVENT;
- e.GUIEvent.Caller = this;
- e.GUIEvent.Element = nullptr;
- e.GUIEvent.EventType = EGET_SCROLL_BAR_CHANGED;
- Parent->OnEvent(e);
- }
  if (absorb)
  return true;
  }
  break;
  case EET_GUI_EVENT:
  if (event.GUIEvent.EventType == EGET_BUTTON_CLICKED) {
  if (event.GUIEvent.Caller == up_button)
- setPos(scroll_pos - small_step);
+ setPosInterpolated(getTargetPos() - small_step);
  else if (event.GUIEvent.Caller == down_button)
- setPos(scroll_pos + small_step);
-
- SEvent e;
- e.EventType = EET_GUI_EVENT;
- e.GUIEvent.Caller = this;
- e.GUIEvent.Element = nullptr;
- e.GUIEvent.EventType = EGET_SCROLL_BAR_CHANGED;
- Parent->OnEvent(e);
+ setPosInterpolated(getTargetPos() + small_step);
  return true;
  } else if (event.GUIEvent.EventType == EGET_ELEMENT_FOCUS_LOST)
  if (event.GUIEvent.Caller == this)
@@ -102,14 +88,7 @@ bool GUIScrollBar::OnEvent(const SEvent &event)
  if (Environment->hasFocus(this)) {
  s8 d = event.MouseInput.Wheel < 0 ? -1 : 1;
  s8 h = is_horizontal ? 1 : -1;
- setPos(getPos() + (d * small_step * h));
-
- SEvent e;
- e.EventType = EET_GUI_EVENT;
- e.GUIEvent.Caller = this;
- e.GUIEvent.Element = nullptr;
- e.GUIEvent.EventType = EGET_SCROLL_BAR_CHANGED;
- Parent->OnEvent(e);
+ setPosInterpolated(getTargetPos() + (d * small_step * h));
  return true;
  }
  break;
@@ -228,11 +207,45 @@ void GUIScrollBar::draw()
  IGUIElement::draw();
 }
 
+static inline s32 interpolate_scroll(s32 from, s32 to, f32 amount)
+{
+ s32 step = core::round32((to - from) * core::clamp(amount, 0.001f, 1.0f));
+ if (step == 0)
+ return to;
+ return from + step;
+}
+
+void GUIScrollBar::interpolatePos()
+{
+ if (target_pos.has_value()) {
+ // Adjust to match 60 FPS. This also means that interpolation is
+ // effectively disabled at <= 30 FPS.
+ f32 amount = 0.5f * (last_delta_ms / 16.667f);
+ setPosRaw(interpolate_scroll(scroll_pos, *target_pos, amount));
+ if (scroll_pos == target_pos)
+ target_pos = std::nullopt;
+
+ SEvent e;
+ e.EventType = EET_GUI_EVENT;
+ e.GUIEvent.Caller = this;
+ e.GUIEvent.Element = nullptr;
+ e.GUIEvent.EventType = EGET_SCROLL_BAR_CHANGED;
+ Parent->OnEvent(e);
+ }
+}
+
+void GUIScrollBar::OnPostRender(u32 time_ms)
+{
+ last_delta_ms = porting::getDeltaMs(last_time_ms, time_ms);
+ last_time_ms = time_ms;
+ interpolatePos();
+}
+
 void GUIScrollBar::updateAbsolutePosition()
 {
  IGUIElement::updateAbsolutePosition();
  refreshControls();
- setPos(scroll_pos);
+ updatePos();
 }
 
 s32 GUIScrollBar::getPosFromMousePos(const core::position2di &pos) const
@@ -250,7 +263,12 @@ s32 GUIScrollBar::getPosFromMousePos(const core::position2di &pos) const
  return core::isnotzero(range()) ? s32(f32(p) / f32(w) * range() + 0.5f) + min_pos : 0;
 }
 
-void GUIScrollBar::setPos(const s32 &pos)
+void GUIScrollBar::updatePos()
+{
+ setPosRaw(scroll_pos);
+}
+
+void GUIScrollBar::setPosRaw(const s32 &pos)
 {
  s32 thumb_area = 0;
  s32 thumb_min = 0;
@@ -276,6 +294,23 @@ void GUIScrollBar::setPos(const s32 &pos)
  border_size;
 }
 
+void GUIScrollBar::setPos(const s32 &pos)
+{
+ setPosRaw(pos);
+ target_pos = std::nullopt;
+}
+
+void GUIScrollBar::setPosInterpolated(const s32 &pos)
+{
+ s32 clamped = core::s32_clamp(pos, min_pos, max_pos);
+ if (scroll_pos != clamped) {
+ target_pos = clamped;
+ interpolatePos();
+ } else {
+ target_pos = std::nullopt;
+ }
+}
+
 void GUIScrollBar::setSmallStep(const s32 &step)
 {
  small_step = step > 0 ? step : 10;
@@ -295,7 +330,7 @@ void GUIScrollBar::setMax(const s32 &max)
  bool enable = core::isnotzero(range());
  up_button->setEnabled(enable);
  down_button->setEnabled(enable);
- setPos(scroll_pos);
+ updatePos();
 }
 
 void GUIScrollBar::setMin(const s32 &min)
@@ -307,13 +342,13 @@ void GUIScrollBar::setMin(const s32 &min)
  bool enable = core::isnotzero(range());
  up_button->setEnabled(enable);
  down_button->setEnabled(enable);
- setPos(scroll_pos);
+ updatePos();
 }
 
 void GUIScrollBar::setPageSize(const s32 &size)
 {
  page_size = size;
- setPos(scroll_pos);
+ updatePos();
 }
 
 void GUIScrollBar::setArrowsVisible(ArrowVisibility visible)
@@ -327,6 +362,15 @@ s32 GUIScrollBar::getPos() const
  return scroll_pos;
 }
 
+s32 GUIScrollBar::getTargetPos() const
+{
+ if (target_pos.has_value()) {
+ s32 clamped = core::s32_clamp(*target_pos, min_pos, max_pos);
+ return clamped;
+ }
+ return scroll_pos;
+}
+
 void GUIScrollBar::refreshControls()
 {
  IGUISkin *skin = Environment->getSkin();

src/gui/guiScrollBar.h

@@ -13,6 +13,7 @@ the arrow buttons where there is insufficient space.
 #pragma once
 
 #include "irrlichttypes_extrabloated.h"
+#include <optional>
 
 class ISimpleTextureSource;
 
@@ -33,21 +34,30 @@ class GUIScrollBar : public IGUIElement
  DEFAULT
  };
 
- virtual void draw();
- virtual void updateAbsolutePosition();
- virtual bool OnEvent(const SEvent &event);
+ virtual void draw() override;
+ virtual void updateAbsolutePosition() override;
+ virtual bool OnEvent(const SEvent &event) override;
+ virtual void OnPostRender(u32 time_ms) override;
 
  s32 getMax() const { return max_pos; }
  s32 getMin() const { return min_pos; }
  s32 getLargeStep() const { return large_step; }
  s32 getSmallStep() const { return small_step; }
  s32 getPos() const;
+ s32 getTargetPos() const;
 
  void setMax(const s32 &max);
  void setMin(const s32 &min);
  void setSmallStep(const s32 &step);
  void setLargeStep(const s32 &step);
+ //! Sets a position immediately, aborting any ongoing interpolation.
+ // setPos does not send EGET_SCROLL_BAR_CHANGED events for you.
  void setPos(const s32 &pos);
+ //! Sets a target position for interpolation.
+ // If you want to do an interpolated addition, use
+ // setPosInterpolated(getTargetPos() + x).
+ // setPosInterpolated takes care of sending EGET_SCROLL_BAR_CHANGED events.
+ void setPosInterpolated(const s32 &pos);
  void setPageSize(const s32 &size);
  void setArrowsVisible(ArrowVisibility visible);
 
@@ -79,4 +89,11 @@ class GUIScrollBar : public IGUIElement
  video::SColor current_icon_color;
 
  ISimpleTextureSource *m_tsrc;
+
+ void setPosRaw(const s32 &pos);
+ void updatePos();
+ std::optional<s32> target_pos;
+ u32 last_time_ms = 0;
+ u32 last_delta_ms = 17; // assume 60 FPS
+ void interpolatePos();
 };

src/gui/guiTable.cpp

@@ -869,7 +869,7 @@ bool GUITable::OnEvent(const SEvent &event)
  core::position2d<s32> p(event.MouseInput.X, event.MouseInput.Y);
 
  if (event.MouseInput.Event == EMIE_MOUSE_WHEEL) {
- m_scrollbar->setPos(m_scrollbar->getPos() +
+ m_scrollbar->setPosInterpolated(m_scrollbar->getTargetPos() +
  (event.MouseInput.Wheel < 0 ? -3 : 3) *
  - (s32) m_rowheight / 2);
  return true;