More drawing API work, including some Windows code so I don't forget important implementation details.

gtkarea/draw.c

@@ -48,6 +48,20 @@ void uiDrawRectangle(uiDrawContext *c, intmax_t x, intmax_t y, intmax_t width, i
 	cairo_rectangle(c->cr, (double) x + 0.5, (double) y + 0.5, width, height);
 }
 
+void uiDrawArc(uiDrawContext *c, intmax_t xCenter, intmax_t yCenter, intmax_t radius, double startAngle, double endAngle, int lineFromCurrentPointToStart)
+{
+	if (!lineFromCurrentPointToStart)
+		cairo_new_sub_path(c->cr);
+	// the Windows AngleArc() function only goes counterclockwise, so our uiDrawArc() function does too
+	// simulate it in cairo by drawing a negative arc from end to start
+	cairo_arc_negative(c->cr,
+		((double) xCenter) + 0.5,
+		((double) yCenter) + 0.5,
+		radius,
+		endAngle,
+		startAngle);
+}
+
 void uiDrawCloseFigure(uiDrawContext *c)
 {
 	cairo_close_path(c->cr);

gtkarea/draw_windows.c

@@ -0,0 +1,120 @@
+// 7 september 2015
+#include "area.h"
+
+struct uiDrawContext {
+	HDC mainDC;
+
+	// when drawing in RGBA mode, we need to use this
+	HDC alphaDC;
+	HBITMAP alphaBitmap;
+
+	// and this is the DC we actually draw to, either mainDC or alphaDC
+	HDC currentDC;
+
+	// source color
+	BOOL useRGB;
+	BOOL useAlpha;
+	uint8_t r;
+	uint8_t g;
+	uint8_t b;
+	uint8_t a;
+};
+
+uiDrawContext *newContext(HDC dc)
+{
+	uiDrawContext *c;
+
+	c = (uiDrawContext *) g_malloc0(sizeof (uiDrawContext));
+	c->mainDC = dc;
+	return c;
+}
+
+void uiDrawBeginPathRGB(uiDrawContext *c, uint8_t r, uint8_t g, uint8_t b)
+{
+	c->useRGB = TRUE;
+	c->useAlpha = FALSE;
+	c->r = r;
+	c->g = g;
+	c->b = b;
+	c->currentDC = c->mainDC;
+	if (BeginPath(c->currentDC) == 0)
+		logLastError("error beginning new path in uiDrawBeginPathRGB()");
+}
+
+void uiDrawBeginPathRGBA(uiDrawContext *c, uint8_t r, uint8_t g, uint8_t b, uint8_t a)
+{
+	// TODO
+}
+
+void uiDrawMoveTo(uiDrawContext *c, intmax_t x, intmax_t y)
+{
+	if (MoveToEx(c->currentDC, x, y, NULL) == 0)
+		logLastError("error moving to point in uiDrawMoveTo()");
+}
+
+void uiDrawLineTo(uiDrawContext *c, intmax_t x, intmax_t y)
+{
+	if (LineTo(c->currentDC, x, y) == 0)
+		logLastError("error drawing line in uiDrawLineTo()");
+}
+
+void uiDrawRectangle(uiDrawContext *c, intmax_t x, intmax_t y, intmax_t width, intmax_t height)
+{
+	if (Rectangle(c->currentDC, x, y, x + width, y + height) == 0)
+		logLastError("error drawing rectangle in uiDrawRectangle()");
+}
+
+void uiDrawArc(uiDrawContext *c, intmax_t xCenter, intmax_t yCenter, intmax_t radius, double startAngle, double endAngle, int lineFromCurrentPointToStart)
+{
+	if (!lineFromCurrentPointToStart) {
+		// TODO
+	}
+	// TODO convert radians to degrees
+	if (AngleArc(c->currentDC,
+		xCenter, yCenter
+		radius,
+		startAngle,
+		// the "sweep angle" is relative to the start angle, not to 0
+		endAngle - startAngle) == 0)
+		logLastError("error drawing arc in uiDrawArc()");
+}
+
+void uiDrawCloseFigure(uiDrawContext *c)
+{
+	if (CloseFigure(c->currentDC) == 0)
+		logLastError("error closing figure in uiDrawCloseFigure()");
+}
+
+void uiDrawStroke(uiDrawContext *c, uiDrawStrokeParams *p)
+{
+	// TODO
+
+	switch (p->Cap) {
+	case uiDrawLineCapFlat:
+		break;
+	case uiDrawLineCapRound:
+		break;
+	case uiDrawLineCapSquare:
+		break;
+	}
+	switch (p->Join) {
+	case uiDrawLineJoinMiter:
+		break;
+	case uiDrawLineJoinRound:
+		break;
+	case uiDrawLineJoinBevel:
+		break;
+	}
+}
+
+void uiDrawFill(uiDrawContext *c, uiDrawFillMode mode)
+{
+	// TODO
+
+	switch (mode) {
+	case uiDrawFillModeWinding:
+		break;
+	case uiDrawFillModeAlternate:
+		break;
+	}
+}

gtkarea/main.c

@@ -1,4 +1,6 @@
 // 4 september 2015
+#define _GNU_SOURCE
+#include <math.h>
 #include "area.h"
 
 // #qo pkg-config: gtk+-3.0
@@ -48,6 +50,31 @@ static void handlerDraw(uiAreaHandler *a, uiArea *area, uiAreaDrawParams *p)
 	sp.Thickness = 1;
 	sp.MiterLimit = uiDrawDefaultMiterLimit;
 	uiDrawStroke(p->Context, &sp);
+
+	uiDrawBeginPathRGB(p->Context, 0x80, 0xC0, 0x00);
+	uiDrawMoveTo(p->Context, 400, 100);
+	uiDrawArc(p->Context,
+		400, 100,
+		50,
+		30. * (M_PI / 180.),
+		// note the end angle here
+		// in GDI, the second angle to AngleArc() is relative to the start, not to 0
+		330. * (M_PI / 180.),
+		1);
+	// TODO add a checkbox for this
+	uiDrawLineTo(p->Context, 400, 100);
+	uiDrawArc(p->Context,
+		510, 100,
+		50,
+		30. * (M_PI / 180.),
+		330. * (M_PI / 180.),
+		0);
+	uiDrawCloseFigure(p->Context);
+	sp.Cap = uiDrawLineCapFlat;
+	sp.Join = uiDrawLineJoinMiter;
+	sp.Thickness = 1;
+	sp.MiterLimit = uiDrawDefaultMiterLimit;
+	uiDrawStroke(p->Context, &sp);
 }
 
 static uintmax_t handlerHScrollMax(uiAreaHandler *a, uiArea *area)

gtkarea/ui.h

@@ -78,6 +78,8 @@ void uiDrawBeginPathRGBA(uiDrawContext *, uint8_t, uint8_t, uint8_t, uint8_t);
 void uiDrawMoveTo(uiDrawContext *, intmax_t, intmax_t);
 void uiDrawLineTo(uiDrawContext *, intmax_t, intmax_t);
 void uiDrawRectangle(uiDrawContext *, intmax_t, intmax_t, intmax_t, intmax_t);
+// notes: angles are both relative to 0 and go counterclockwise
+void uiDrawArc(uiDrawContext *, intmax_t, intmax_t, intmax_t, double, double, int);
 void uiDrawCloseFigure(uiDrawContext *);
 
 void uiDrawStroke(uiDrawContext *, uiDrawStrokeParams *);
@@ -87,8 +89,8 @@ void uiDrawFill(uiDrawContext *, uiDrawFillMode);
 // cairo			gdi						core graphics
 // move_to		MoveToEx				MoveToPoint
 // line_to			LineTo					AddLineToPoint
-// arc			Arc/ArcTo/AngleArc/Ellipse	AddArc/AddArcToPoint/AddEllipseInRect
-// arc_negative	Pie						AddArc/AddArcToPoint
+// arc			Arc/ArcTo/AngleArc/Pie		AddArc/AddArcToPoint/AddEllipseInRect
+// arc_negative	Arc/ArcTo/AngleArc/Pie		AddArc/AddArcToPoint
 // curve_to		PolyBezier/PolyBezierTo		AddCurveToPoint
 // rectangle		Rectangle					AddRect
 // [arc functions?]	Chord					[arc functions?]
@@ -112,3 +114,26 @@ void uiDrawFill(uiDrawContext *, uiDrawFillMode);
 // - arbitrary patterns
 // - solid colors, arbitrary spaces
 // - shadows
+
+// arcs
+// cairo_arc/arc_negative
+// - parameters: center, radius, angle1 radians, angle2 radins
+// - if angle2 < angle1, TODO
+// - if angle2 > angle1, TODO
+// - line segment from current point to beginning of arc
+// - arc: clockwise, arc_negative: counterclockwise
+// - circular
+// GDI Arc/Pie
+// - parameters: bounding box, start point, end point
+// - current position not used/changed
+// - either clockwise or counterclockwise
+// - elliptical
+// GDI ArcTo
+// - same as Arc except line segment from current point to beginning of arc
+// - there does not appear to be a PieTo
+// GDI AngleArc
+// - parameters: center, radius, angle1 degrees, angle2 degrees
+// - line segment from current position to beginning of arc
+// - counterclockwise
+// - circular
+// - can be used to draw pies too; MSDN example demonstrates