AffineTransform t = AffineTransform.getScaleInstance(vt.getScaleX(), vt.getScaleY());
t.translate(-tx,-ty);
canvas.viewTransform(t, false);
} else if (c == '+' || c == '=') {
vt.scale(2, 2);
canvas.viewTransform(vt, false);
} else if (c == '-' || c == '_') {
vt.scale(.5,.5);
canvas.viewTransform(vt, false);
} else if (c == 'z' || c == 'Z') {
canvas.zoomFit();