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feat: add overscroll when constrained area is smaller than viewport

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Arnošt Pleskot 2023-07-09 11:56:23 +02:00
parent 19ba107041
commit bc44c3f947
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1 changed files with 64 additions and 43 deletions
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107
src/components/App.tsx
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@ -7690,55 +7690,76 @@ class App extends React.Component<AppProps, AppState> {
const overscrollAllowanceY =
OVERSCROLL_ALLOWANCE_PERCENTAGE * scrollableHeight;
// Define the maximum and minimum scroll for each axis based on the cursor button state
const maxScrollX =
cursorButton === "down"
? scrollConstraints.x + overscrollAllowanceX
: scrollConstraints.x;
const minScrollX =
cursorButton === "down"
? scrollConstraints.x -
scrollableWidth +
width / zoom.value -
overscrollAllowanceX
: scrollConstraints.x - scrollableWidth + width / zoom.value;
const maxScrollY =
cursorButton === "down"
? scrollConstraints.y + overscrollAllowanceY
: scrollConstraints.y;
const minScrollY =
cursorButton === "down"
? scrollConstraints.y -
scrollableHeight +
height / zoom.value -
overscrollAllowanceY
: scrollConstraints.y - scrollableHeight + height / zoom.value;
// Constrain the scroll within the scroll constraints, with overscroll allowance if the cursor button is down
constrainedScrollX = Math.min(maxScrollX, Math.max(scrollX, minScrollX));
constrainedScrollY = Math.min(maxScrollY, Math.max(scrollY, minScrollY));
// Check if the zoom value requires adjustment for a centered view
// When we are zoomed out enough to contain constrained area in the viewport we will center the view
const shouldAdjustForCenteredView =
zoom.value <= maxZoomX || zoom.value <= maxZoomY;
if (shouldAdjustForCenteredView) {
// Adjust the scroll position for a centered view based on the zoom value
const adjustScrollForCenteredView = (zoomValue: number) => {
if (zoomValue <= maxZoomX) {
const centeredScrollX = (scrollableWidth - width / zoomValue) / -2;
constrainedScrollX = scrollConstraints.x + centeredScrollX;
}
if (zoomValue <= maxZoomY) {
const centeredScrollY = (scrollableHeight - height / zoomValue) / -2;
constrainedScrollY = scrollConstraints.y + centeredScrollY;
}
};
// When viewport is smaller than the scrollable area, user can pan freely within the constrained area,
// otherwilse the viewport is centered to the center of the scrollable area
let maxScrollX;
let minScrollX;
let maxScrollY;
let minScrollY;
adjustScrollForCenteredView(zoom.value);
// Get center of scrollable area
const constrainedScrollCenterX =
scrollConstraints.x + (scrollableWidth - width / zoom.value) / -2;
const constrainedScrollCenterY =
scrollConstraints.y + (scrollableHeight - height / zoom.value) / -2;
switch (true) {
case cursorButton === "down" && shouldAdjustForCenteredView:
// case when cursor button is down and we should adjust for centered view
maxScrollX = constrainedScrollCenterX + overscrollAllowanceX;
minScrollX = constrainedScrollCenterX - overscrollAllowanceX;
maxScrollY = constrainedScrollCenterY + overscrollAllowanceY;
minScrollY = constrainedScrollCenterY - overscrollAllowanceY;
break;
case cursorButton === "down" && !shouldAdjustForCenteredView:
// case when cursor button is down and we should not adjust for centered view
maxScrollX = scrollConstraints.x + overscrollAllowanceX;
minScrollX =
scrollConstraints.x -
scrollableWidth +
width / zoom.value -
overscrollAllowanceX;
maxScrollY = scrollConstraints.y + overscrollAllowanceY;
minScrollY =
scrollConstraints.y -
scrollableHeight +
height / zoom.value -
overscrollAllowanceY;
break;
case cursorButton !== "down" && shouldAdjustForCenteredView:
// case when cursor button is not down and we should adjust for centered view
maxScrollX = constrainedScrollCenterX;
minScrollX = constrainedScrollCenterX;
maxScrollY = constrainedScrollCenterY;
minScrollY = constrainedScrollCenterY;
break;
default:
// case when cursor button is not down and we should not adjust for centered view
maxScrollX = scrollConstraints.x;
minScrollX = scrollConstraints.x - scrollableWidth + width / zoom.value;
maxScrollY = scrollConstraints.y;
minScrollY =
scrollConstraints.y - scrollableHeight + height / zoom.value;
break;
}
// Constrain the scroll within the scroll constraints
constrainedScrollX = Math.min(maxScrollX, Math.max(scrollX, minScrollX));
constrainedScrollY = Math.min(maxScrollY, Math.max(scrollY, minScrollY));
// Check if the new state differs from the old state
const stateChanged =
constrainedScrollX !== scrollX || constrainedScrollY !== scrollY;