Add `FramebufferWidget::dirtyOnSubpixelChange` setting. Disable it for the FramebufferWidget that contains the RackRail.

include/widget/FramebufferWidget.hpp

@@ -18,6 +18,8 @@ struct FramebufferWidget : Widget {
 	bool dirty = true;
 	bool bypass = false;
 	float oversample = 1.0;
+	/** Redraw when the world offset of the FramebufferWidget changes its fractional value. */
+	bool dirtyOnSubpixelChange = true;
 
 	FramebufferWidget();
 	~FramebufferWidget();

src/app/RackWidget.cpp

@@ -71,6 +71,8 @@ RackWidget::RackWidget() {
 	railFb = new widget::FramebufferWidget;
 	railFb->box.size = math::Vec();
 	railFb->oversample = 1.0;
+	// Don't redraw when the world offset of the rail FramebufferWidget changes its fractional value.
+	railFb->dirtyOnSubpixelChange = false;
 	{
 		RackRail* rail = new RackRail;
 		rail->box.size = math::Vec();

src/widget/FramebufferWidget.cpp

@@ -80,7 +80,7 @@ void FramebufferWidget::step() {
 		localBox = getChildrenBoundingBox();
 	}
 
-	// DEBUG("%g %g %g %g, %g %g, %g %g", RECT_ARGS(localBox), VEC_ARGS(internal->fbOffsetF), VEC_ARGS(internal->fbScale));
+	// DEBUG("rendering FramebufferWidget localBox (%g %g %g %g) fbOffset (%g %g) fbScale (%g %g)", RECT_ARGS(localBox), VEC_ARGS(internal->fbOffsetF), VEC_ARGS(internal->fbScale));
 	// Transform to world coordinates, then expand to nearest integer coordinates
 	math::Vec min = localBox.getTopLeft().mult(internal->fbScale).plus(internal->fbOffsetF).floor();
 	math::Vec max = localBox.getBottomRight().mult(internal->fbScale).plus(internal->fbOffsetF).ceil();
@@ -178,7 +178,7 @@ void FramebufferWidget::draw(const DrawArgs& args) {
 	math::Vec offsetI = offset.floor();
 	internal->offsetF = offset.minus(offsetI);
 
-	if (!math::isNear(internal->offsetF.x, internal->fbOffsetF.x, 0.01f) || !math::isNear(internal->offsetF.y, internal->fbOffsetF.y, 0.01f)) {
+	if (dirtyOnSubpixelChange && !(math::isNear(internal->offsetF.x, internal->fbOffsetF.x, 0.01f) && math::isNear(internal->offsetF.y, internal->fbOffsetF.y, 0.01f))) {
 		// If drawing to a new subpixel location, rerender in the next frame.
 		// DEBUG("%p dirty subpixel", this);
 		dirty = true;