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QuickShow: Use a better formula for zooming.

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Now the pixel under the cursor doesn't move, which is more consistent
with other image viewers (e.g. GwenView and IrfanView). Also switch
m_pan_origin to use window space to have less space transformations.
This commit is contained in:
Oleg Sikorskiy 2021-03-15 22:34:19 +03:00 committed by Andreas Kling
parent d6239b691f
commit ee64c814c6
1 changed files with 14 additions and 11 deletions
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25
Userland/Applications/QuickShow/QSWidget.cpp
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@ -156,12 +156,11 @@ void QSWidget::relayout()
if (m_bitmap.is_null())
return;
float scale_factor = (float)m_scale / 100.0f;
Gfx::IntSize new_size = m_bitmap_rect.size();
Gfx::IntPoint new_location;
new_location.set_x((width() / 2) - (new_size.width() / 2) - (m_pan_origin.x() * scale_factor));
new_location.set_y((height() / 2) - (new_size.height() / 2) - (m_pan_origin.y() * scale_factor));
new_location.set_x((width() / 2) - (new_size.width() / 2) - m_pan_origin.x());
new_location.set_y((height() / 2) - (new_size.height() / 2) - m_pan_origin.y());
m_bitmap_rect.set_location(new_location);
update();
@ -208,10 +207,9 @@ void QSWidget::mousemove_event(GUI::MouseEvent& event)
return;
auto delta = event.position() - m_click_position;
float scale_factor = (float)m_scale / 100.0f;
m_pan_origin = m_saved_pan_origin.translated(
-delta.x() / scale_factor,
-delta.y() / scale_factor);
-delta.x(),
-delta.y());
relayout();
}
@ -231,13 +229,18 @@ void QSWidget::mousewheel_event(GUI::MouseEvent& event)
auto old_scale_factor = (float)m_scale / 100.0f;
auto new_scale_factor = (float)new_scale / 100.0f;
// focus_point is the window position the cursor is pointing to.
// The pixel (in image space) the cursor points to is located at
// (m_pan_origin + focus_point) / scale_factor.
// We want the image after scaling to be panned in such a way that the cursor
// will still point to the same image pixel. Basically, we need to solve
// (m_pan_origin + focus_point) / old_scale_factor = (new_m_pan_origin + focus_point) / new_scale_factor.
auto focus_point = Gfx::FloatPoint(
m_pan_origin.x() - ((float)event.x() - (float)width() / 2.0) / old_scale_factor,
m_pan_origin.y() - ((float)event.y() - (float)height() / 2.0) / old_scale_factor);
(float)event.x() - (float)width() / 2.0,
(float)event.y() - (float)height() / 2.0);
m_pan_origin = Gfx::FloatPoint(
focus_point.x() - new_scale_factor / old_scale_factor * (focus_point.x() - m_pan_origin.x()),
focus_point.y() - new_scale_factor / old_scale_factor * (focus_point.y() - m_pan_origin.y()));
// A little algebra shows that new m_pan_origin equals to:
m_pan_origin = (m_pan_origin + focus_point) * (new_scale_factor / old_scale_factor) - focus_point;
set_scale(new_scale);
}