UXGdiGraphics

UXGdiGraphics is the Win32 realization of UXGraphics, and the first sibling of UXGemGraphics.

#use <UXKit>            // or #import "UXGdiGraphics.xc"

The same primitives, a different surface

Every drawRect in the toolkit calls the same small set of methods. This class implements them over a device context rather than a VDI workstation.

Incoming coordinates are bounds-relative, and the bound origin makes them absolute, as on GEM. Because the contract does not change, a view’s drawing body is written once and is correct on every backend.

GDI’s y grows down, as GEM’s does, so nothing needs flipping.

Two implementations define the protocol

This class shows that UXGraphics is an interface and not a description of the VDI. Two implementations satisfy it: one over an early-80s workstation model, the other over a device-context model. The later backends implement the same methods.

It has no theme art

hasThemeArt()      // false

Windows has no equivalent of GEM’s drawable theme slices, so drawTheme has nothing to call and the toolkit draws the pieces itself.

Answering false is safe because there is a neutral fallback. A capability query asks whether the backend can do something, not whether it must, and the toolkit always has an answer for no.

It strokes natively

strokesNatively()      // true

UXPainter.strokePath hands GDI the path, and GDI draws the curve at its own precision with its own joins, instead of the toolkit offsetting a whole-pixel polyline.

The stroke width rounds to a whole pixel

// strokeNative* take a double, but GDI's pen is an integer:
// 1.536 is drawn at 2, 1.0 at 1, 0 at 1.

A GDI pen has no fractional width, so the seam’s double width — which the five real strokers draw exactly — is rounded to the nearest pixel here (a width below half a pixel becomes a hairline rather than nothing). The VDI is the same. It is the one place where the width the caller passed and the width drawn are not the same number, and it errs towards ink.

It does not dash natively

dashesNatively()       // false

ExtCreatePen takes PS_DASH only on a cosmetic pen: one pixel wide, no joins, no phase, no width. A dash that cannot honour the caller’s width or phase is a worse answer than none, so a dashed border here goes through UXPainter’s neutral dasher, which emits the ON pieces of the flattened centreline.

Arrowheads stay neutral, because GDI has none. All six hosted backends use this split: the platform draws what it draws well, and the toolkit draws what no platform has.

Pens map to a colour table

The toolkit draws with VDI pen indices. This vocabulary keeps the index-to-RGB table (penColor) that converts them for GDI.

UXCanvasGraphics mirrors the same table, split per channel because the host import signature takes r, g and b separately. Keeping the table in several places has a maintenance cost; in return a pen number means the same colour on every backend.

fillRectRGB and fillPolygonRGB are the true-colour entry points for UXColor-driven drawing that bypasses the palette.