Module pixel_bounds 

Pixel-alignment policy for widget bounds and draw-time translation.

Port of MatterCAD / agg-sharp

GuiWidget.DefaultEnforceIntegerBounds (static) controls whether widgets round their bounds / padding / margin to the physical pixel grid, and is then mirrored on each widget as EnforceIntegerBounds so individual widgets can opt out (e.g. a smooth-scrolling marker or a zoomed canvas that genuinely wants sub-pixel positioning).

We default to true because the vast majority of UI widgets want crisp text and strokes — fractional bounds are the exception, not the rule.

Read site

paint_subtree reads the effective flag (widget’s override, falling back to the global default) and rounds the child-translation to the nearest integer pixel before calling the child’s paint. That single snap kills fractional CTM accumulated by cumulative-heights flex layout (e.g. Label line_h = font_size × 1.5 is fractional for most font sizes), which is what caused the Y-axis pixel fringe on crisp rectangle fills downstream.

Opt-out

// Globally disable (rare — only for fully sub-pixel render targets):
agg_gui::pixel_bounds::set_default_enforce_integer_bounds(false);

// Per-widget:
my_widget.widget_base_mut().enforce_integer_bounds = false;

Functions

default_enforce_integer_bounds

Current process-wide default used to initialise each new widget’s enforce_integer_bounds field.

set_default_enforce_integer_bounds

Change the process-wide default. Only affects widgets constructed after this call; existing widgets keep whichever value they captured when they were built. Match MatterCAD semantics (DefaultEnforceIntegerBounds setter) exactly.