Extra image pixels to push the plot-area top edge down for a twiny (top x-axis), beyond the default top margin.
The raster/PDF backends stack the top band upward from the plot-area top edge as: top tick labels, then the top axis label, then the title. Without a twiny only the title sits above the axes, and the default top margin already holds it inside the canvas. A twiny inserts the tick labels and the top axis label below the title, so the stack grows and the upper elements clip at y=0. This returns that added height.
Tick and axis label heights match DEFAULT_FONT_SIZE points scaled to device pixels by DPI; pads match the constants the label placement applies (X_TICK_LABEL_TOP_PAD, CANVAS_EDGE_PADDING_PX). The added TITLE_VERTICAL_OFFSET is the gap the title now needs above the top-axis block. The title's own height is not added: the default top margin already reserves it, and with a twiny the title simply moves from just above the axes to the top of this taller stack.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| real(kind=wp), | intent(in) | :: | dpi | |||
| logical, | intent(in) | :: | has_top_xlabel |