From ee64c814c623b85a2a427668ce4e391fc7411b4b Mon Sep 17 00:00:00 2001 From: Oleg Sikorskiy Date: Mon, 15 Mar 2021 22:34:19 +0300 Subject: [PATCH] QuickShow: Use a better formula for zooming. 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. --- Userland/Applications/QuickShow/QSWidget.cpp | 25 +++++++++++--------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/Userland/Applications/QuickShow/QSWidget.cpp b/Userland/Applications/QuickShow/QSWidget.cpp index fc515a87f5..23bfe8bfd1 100644 --- a/Userland/Applications/QuickShow/QSWidget.cpp +++ b/Userland/Applications/QuickShow/QSWidget.cpp @@ -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); }