private ImmutableViewportMetrics getValidViewportMetrics(
ImmutableViewportMetrics viewportMetrics) {
/* First, we adjust the zoom factor so that we can make no overscrolled area visible. */
float zoomFactor = viewportMetrics.zoomFactor;
RectF pageRect = viewportMetrics.getPageRect();
RectF viewport = viewportMetrics.getViewport();
float focusX = viewport.width() / 2.0f;
float focusY = viewport.height() / 2.0f;
float minZoomFactor = 0.0f;
float maxZoomFactor = MAX_ZOOM;
ZoomConstraints constraints = mTarget.getZoomConstraints();
if (constraints.getMinZoom() > 0) minZoomFactor = constraints.getMinZoom();
if (constraints.getMaxZoom() > 0) maxZoomFactor = constraints.getMaxZoom();
if (!constraints.getAllowZoom()) {
// If allowZoom is false, clamp to the default zoom level.
maxZoomFactor = minZoomFactor = constraints.getDefaultZoom();
}
// Ensure minZoomFactor keeps the page at least as big as the viewport.
if (pageRect.width() > 0) {
float scaleFactor = viewport.width() / pageRect.width();
minZoomFactor = Math.max(minZoomFactor, zoomFactor * scaleFactor);
if (viewport.width() > pageRect.width()) focusX = 0.0f;
}
if (pageRect.height() > 0) {
float scaleFactor = viewport.height() / pageRect.height();
minZoomFactor = Math.max(minZoomFactor, zoomFactor * scaleFactor);
if (viewport.height() > pageRect.height()) focusY = 0.0f;
}
maxZoomFactor = Math.max(maxZoomFactor, minZoomFactor);
if (zoomFactor < minZoomFactor) {
// if one (or both) of the page dimensions is smaller than the viewport,
// zoom using the top/left as the focus on that axis. this prevents the
// scenario where, if both dimensions are smaller than the viewport, but
// by different scale factors, we end up scrolled to the end on one axis
// after applying the scale
PointF center = new PointF(focusX, focusY);
viewportMetrics = viewportMetrics.scaleTo(minZoomFactor, center);
} else if (zoomFactor > maxZoomFactor) {
PointF center = new PointF(viewport.width() / 2.0f, viewport.height() / 2.0f);
viewportMetrics = viewportMetrics.scaleTo(maxZoomFactor, center);
}
/* Now we pan to the right origin. */
viewportMetrics = viewportMetrics.clamp();
return viewportMetrics;
}
