Constraints property

Constraints exposes the four sub-properties MinWidth, MaxWidth, MinHeight and MaxHeight (all default 0 = no limit). They clamp the resize logic driven by Align, Anchors, or explicit SetBounds calls, preventing the viewer from collapsing below a usable minimum or growing beyond a sensible maximum.

For PDF reader applications the minimum dimensions matter most: rendering becomes uncomfortable below roughly 240 x 180, and the scroll bars start to fight for space with the page itself. Setting MinWidth := 320 and MinHeight := 240 avoids that visual breakdown while still letting users dock the viewer narrowly.

When a constraint kicks in, the active FitMode recalculates the page zoom against the clamped client size. This guarantees that fit-to-width and fit-to-page never produce zero or negative pixel sizes that would otherwise cause PDFium to skip rendering.

• Persistent — the four numeric sub-properties are serialized to the form file. Designed to be set in the Object Inspector or via code before the form is shown.
• Applies to both VCL and LCL. Under LCL Constraints additionally interacts with widget-set themed minimum sizes, but the PDFium control's own logic uses only the values declared here.
• Leave any sub-property at 0 to express "no limit" on that axis — for example a viewer that should never be wider than 800 px can have MaxWidth := 800 while keeping MinWidth := 0.
• Constraints take effect at the moment of every resize, so changing them at run-time may trigger an immediate OnResize and a re-fit if the current size violates the new range.