Added Image and renamed the BrushType constants respectively.

draw.go

@@ -206,10 +206,10 @@ type DrawContext struct {
 // TODO disclaimer
 type BrushType int
 const (
-	Solid BrushType = iota
-	LinearGradient
-	RadialGradient
-	Image		// presently unimplemented
+	BrushTypeSolid BrushType = iota
+	BrushTypeLinearGradient
+	BrushTypeRadialGradient
+	BrushTypeImage		// presently unimplemented
 )
 
 // TODO
@@ -270,12 +270,12 @@ func (b *Brush) toC() *C.uiDrawBrush {
 	cb := C.newBrush()
 	cb.Type = C.uiDrawBrushType(b.Type)
 	switch b.Type {
-	case Solid:
+	case BrushTypeSolid:
 		cb.R = C.double(b.R)
 		cb.G = C.double(b.G)
 		cb.B = C.double(b.B)
 		cb.A = C.double(b.A)
-	case LinearGradient, RadialGradient:
+	case BrushTypeLinearGradient, BrushTypeRadialGradient:
 		cb.X0 = C.double(b.X0)
 		cb.Y0 = C.double(b.Y0)
 		cb.X1 = C.double(b.X1)
@@ -291,7 +291,7 @@ func (b *Brush) toC() *C.uiDrawBrush {
 				C.double(s.B),
 				C.double(s.A))
 		}
-	case Image:
+	case BrushTypeImage:
 		panic("unimplemented")
 	default:
 		panic("invalid brush type in Brush.toC()")

image.go

@@ -0,0 +1,58 @@
+// 21 august 2018
+
+package ui
+
+import (
+	"image"
+)
+
+// #include <stdlib.h>
+// #include "ui.h"
+import "C"
+
+// Image stores an image for display on screen.
+// 
+// Images are built from one or more representations, each with the
+// same aspect ratio but a different pixel size. Package ui
+// automatically selects the most appropriate representation for
+// drawing the image when it comes time to draw the image; what
+// this means depends on the pixel density of the target context.
+// Therefore, one can use Image to draw higher-detailed images on
+// higher-density displays. The typical use cases are either:
+// 
+// 	- have just a single representation, at which point all screens
+// 	  use the same image, and thus uiImage acts like a simple
+// 	  bitmap image, or
+// 	- have two images, one at normal resolution and one at 2x
+// 	  resolution; this matches the current expectations of some
+// 	  desktop systems at the time of writing (mid-2018)
+//
+// Image allocates OS resources; you must explicitly free an Image
+// when you are finished with it.
+type Image struct {
+	i	*C.uiImage
+}
+
+// NewImage creates a new Image with the given width and
+// height. This width and height should be the size in points of the
+// image in the device-independent case; typically this is the 1x size.
+func NewImage(width, height float64) *Image {
+	return &Image{
+		i:	C.uiNewImage(C.double(width), C.double(height)),
+	}
+}
+
+// Free frees the Image.
+func (i *Image) Free() {
+	C.uiFreeImage(i.i)
+}
+
+// Append adds the given image as a representation of the Image.
+func (i *Image) Append(img *image.NRGBA) {
+	cpix := C.CBytes(img.Pix)
+	defer C.free(cpix)
+	C.uiImageAppend(i.i, cpix,
+		C.int(img.Rect.Dx()),
+		C.int(img.Rect.Dy()),
+		C.int(img.Stride))
+}

zz_histogram.go

@@ -31,7 +31,7 @@ const (
 // helper to quickly set a brush color
 func mkSolidBrush(color uint32, alpha float64) *ui.Brush {
 	brush := new(ui.Brush)
-	brush.Type = ui.Solid
+	brush.Type = ui.BrushTypeSolid
 	component := uint8((color >> 16) & 0xFF)
 	brush.R = float64(component) / 255
 	component = uint8((color >> 8) & 0xFF)
@@ -125,7 +125,7 @@ func (areaHandler) Draw(a *ui.Area, p *ui.AreaDrawParams) {
 
 	// now get the color for the graph itself and set up the brush
 	graphR, graphG, graphB, graphA := colorButton.Color()
-	brush.Type = ui.Solid
+	brush.Type = ui.BrushTypeSolid
 	brush.R = graphR
 	brush.G = graphG
 	brush.B = graphB