graph: navigate to blocks, not to coordinates

Clicking the minimap panned to the exact coordinate under the pointer and moved
the cursor only if a block happened to sit there. Since one minimap cell covers
many canvas cells, "there" was almost always padding: you got a jump into empty
space and the cursor stayed behind, so you had to click a block afterwards to
actually go anywhere.

Blocks cover a few percent of a laid-out graph -- 4.6% of an 87-block function,
0.8% of a 424-block one -- and the rest is the space that keeps edges apart. So
coordinates are the wrong thing to navigate by here. The minimap now snaps to
the nearest block and takes the cursor with it, and a drag scrubs from block to
block. Distance is measured with the column halved, because cells are twice as
tall as they are wide and otherwise "nearest" is not what looks nearest.

A drag-pan or ctrl+d/pageup that ends with no block on screen at all now eases
to the nearest one too, since an empty screen leaves nothing to navigate back
by. It only fires when nothing is visible, so a deliberate pan is never fought.

0 files changed, 0 insertions, 0 deletions