Built the framework for matrices and transformations and implemented it on the GTK+ backend. Tests to come next.

GNUmakefile

@@ -25,6 +25,7 @@ baseHFILES = \
 baseCFILES = \
 	areaevents.c \
 	control.c \
+	matrix.c \
 	menu.c \
 	ptrarray.c \
 	shouldquit.c \

TODO.md

@@ -1,3 +1,5 @@
+- make sure graphics state is saved and restored around each draw call
+
 - all ports: update state when adding a control to a parent
 - should uiWindowsSizing be computed against the window handle, not the parent?
 

matrix.c

@@ -0,0 +1,17 @@
+// 11 october 2015
+#include "ui.h"
+#include "uipriv.h"
+
+void setIdentity(uiDrawMatrix *m)
+{
+	m->M11 = 1;
+	m->M12 = 0;
+	m->M21 = 0;
+	m->M22 = 1;
+	m->M31 = 0;
+	m->M32 = 0;
+}
+
+// TODO skew
+
+// see windows/draw.c for more information

ui.h

@@ -295,6 +295,7 @@ struct uiAreaDrawParams {
 typedef struct uiDrawPath uiDrawPath;
 typedef struct uiDrawBrush uiDrawBrush;
 typedef struct uiDrawStrokeParams uiDrawStrokeParams;
+typedef struct uiDrawMatrix uiDrawMatrix;
 
 typedef enum uiDrawBrushType uiDrawBrushType;
 typedef struct uiDrawBrushGradientStop uiDrawBrushGradientStop;
@@ -332,6 +333,15 @@ enum uiDrawFillMode {
 	uiDrawFillModeAlternate,
 };
 
+struct uiDrawMatrix {
+	double M11;
+	double M12;
+	double M21;
+	double M22;
+	double M31;
+	double M32;
+};
+
 struct uiDrawBrush {
 	uiDrawBrushType Type;
 
@@ -402,6 +412,21 @@ _UI_EXTERN void uiDrawFill(uiDrawContext *c, uiDrawPath *path, uiDrawBrush *b);
 // - elliptical arcs
 // - quadratic bezier curves
 
+_UI_EXTERN void uiDrawMatrixSetIdentity(uiDrawMatrix *m);
+_UI_EXTERN void uiDrawMatrixTranslate(uiDrawMatrix *m, double x, double y);
+_UI_EXTERN void uiDrawMatrixScale(uiDrawMatrix *m, double x, double y);
+_UI_EXTERN void uiDrawMatrixRotate(uiDrawMatrix *m, double x, double y, double amount);
+_UI_EXTERN void uiDrawMatrixSkew(uiDrawMatrix *m, double x, double y, double amount);
+_UI_EXTERN void uiDrawMatrixMultiply(uiDrawMatrix *dest, uiDrawMatrix *src);
+_UI_EXTERN int uiDrawMatrixInvertible(uiDrawMatrix *m);
+_UI_EXTERN int uiDrawMatrixInvert(uiDrawMatrix *m);
+_UI_EXTERN void uiDrawMatrixTransformPoint(uiDrawMatrix *m, double *x, double *y);
+_UI_EXTERN void uiDrawMatrixTransformSize(uiDrawMatrix *m, double *x, double *y);
+
+_UI_EXTERN void uiDrawSave(uiDrawContext *c);
+_UI_EXTERN void uiDrawRestore(uiDrawContext *c);
+_UI_EXTERN void uiDrawTransform(uiDrawContext *c, uiDrawMatrix *m);
+
 typedef enum uiModifiers uiModifiers;
 
 enum uiModifiers {

uipriv.h

@@ -59,3 +59,6 @@ struct clickCounter {
 extern uintmax_t clickCounterClick(clickCounter *, uintmax_t, intmax_t, intmax_t, uintptr_t, uintptr_t, intmax_t, intmax_t);
 extern void clickCounterReset(clickCounter *);
 extern int fromScancode(uintptr_t, uiAreaKeyEvent *);
+
+// matrix.c
+extern void setIdentity(uiDrawMatrix *);

unix/draw.c

@@ -296,3 +296,128 @@ void uiDrawFill(uiDrawContext *c, uiDrawPath *path, uiDrawBrush *b)
 	cairo_fill(c->cr);
 	cairo_pattern_destroy(pat);
 }
+
+static void m2c(uiDrawMatrix *m, cairo_matrix_t *c)
+{
+	c->xx = m->M11;
+	c->yx = m->M12;
+	c->xy = m->M21;
+	c->yy = m->M22;
+	c->x0 = m->M31;
+	c->y0 = m->M32;
+}
+
+static void c2m(cairo_matrix_t *c, uiDrawMatrix *m)
+{
+	m->M11 = c->xx;
+	m->M12 = c->yx;
+	m->M21 = c->xy;
+	m->M22 = c->yy;
+	m->M31 = c->x0;
+	m->M32 = c->y0;
+}
+
+void uiDrawMatrixSetIdentity(uiDrawMatrix *m)
+{
+	setIdentity(m);
+}
+
+void uiDrawMatrixTranslate(uiDrawMatrix *m, double x, double y)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	cairo_matrix_translate(&c, x, y);
+	c2m(&c, m);
+}
+
+void uiDrawMatrixScale(uiDrawMatrix *m, double x, double y)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	cairo_matrix_scale(&c, x, y);
+	c2m(&c, m);
+}
+
+void uiDrawMatrixRotate(uiDrawMatrix *m, double x, double y, double amount)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	// TODO verify this
+	cairo_matrix_translate(&c, x, y);
+	// TODO explain this
+	cairo_matrix_rotate(&c, -amount);
+	cairo_matrix_translate(&c, -x, -y);
+	c2m(&c, m);
+}
+
+void uiDrawMatrixSkew(uiDrawMatrix *m, double x, double y, double amount)
+{
+	complain("TODO");
+}
+
+void uiDrawMatrixMultiply(uiDrawMatrix *dest, uiDrawMatrix *src)
+{
+	cairo_matrix_t c;
+	cairo_matrix_t d;
+
+	m2c(dest, &c);
+	m2c(src, &d);
+	cairo_matrix_multiply(&c, &c, &d);
+	c2m(&c, dest);
+}
+
+int uiDrawMatrixInvertible(uiDrawMatrix *m)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	return cairo_matrix_invert(&c) == CAIRO_STATUS_SUCCESS;
+}
+
+int uiDrawMatrixInvert(uiDrawMatrix *m)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	if (cairo_matrix_invert(&c) != CAIRO_STATUS_SUCCESS)
+		return 0;
+	c2m(&c, m);
+	return 1;
+}
+
+void uiDrawMatrixTransformPoint(uiDrawMatrix *m, double *x, double *y)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	cairo_matrix_transform_point(&c, x, y);
+}
+
+void uiDrawMatrixTransformSize(uiDrawMatrix *m, double *x, double *y)
+{
+	cairo_matrix_t c;
+
+	m2c(m, &c);
+	cairo_matrix_transform_distance(&c, x, y);
+}
+
+void uiDrawSave(uiDrawContext *c)
+{
+	cairo_save(c->cr);
+}
+
+void uiDrawRestore(uiDrawContext *c)
+{
+	cairo_restore(c->cr);
+}
+
+void uiDrawTransform(uiDrawContext *c, uiDrawMatrix *m)
+{
+	cairo_matrix_t cm;
+
+	m2c(m, &cm);
+	cairo_transform(c->cr, &cm);
+}