Fixed image lists on Windows being NON-premultiplied.

redo/area.go

@@ -5,6 +5,7 @@ package ui
 import (
 	"fmt"
 	"image"
+	"image/draw"
 	"reflect"
 	"unsafe"
 )
@@ -331,7 +332,7 @@ func pixelData(img *image.RGBA) *uint8 {
 // some platforms require pixels in ARGB order in their native endianness (because they treat the pixel array as an array of uint32s)
 // this does the conversion
 // you need to convert somewhere (Windows and cairo give us memory to use; Windows has stride==width but cairo might not)
-func toARGB(i *image.RGBA, memory uintptr, memstride int) {
+func toARGB(i *image.RGBA, memory uintptr, memstride int, toNRGBA bool) {
 	var realbits []byte
 
 	rbs := (*reflect.SliceHeader)(unsafe.Pointer(&realbits))
@@ -340,14 +341,20 @@ func toARGB(i *image.RGBA, memory uintptr, memstride int) {
 	rbs.Cap = rbs.Len
 	p := pixelDataPos(i)
 	q := 0
+	iPix := i.Pix
+	if toNRGBA {		// for Windows image lists
+		j := image.NewNRGBA(i.Rect)
+		draw.Draw(j, j.Rect, i, i.Rect.Min, draw.Src)
+		iPix = j.Pix
+	}
 	for y := i.Rect.Min.Y; y < i.Rect.Max.Y; y++ {
 		nextp := p + i.Stride
 		nextq := q + memstride
 		for x := i.Rect.Min.X; x < i.Rect.Max.X; x++ {
-			argb := uint32(i.Pix[p+3]) << 24 // A
-			argb |= uint32(i.Pix[p+0]) << 16 // R
-			argb |= uint32(i.Pix[p+1]) << 8  // G
-			argb |= uint32(i.Pix[p+2])       // B
+			argb := uint32(iPix[p+3]) << 24 // A
+			argb |= uint32(iPix[p+0]) << 16 // R
+			argb |= uint32(iPix[p+1]) << 8  // G
+			argb |= uint32(iPix[p+2])       // B
 			// the magic of conversion
 			native := (*[4]byte)(unsafe.Pointer(&argb))
 			realbits[q+0] = native[0]

redo/area_unix.go

@@ -223,7 +223,7 @@ func our_area_draw_callback(widget *C.GtkWidget, cr *C.cairo_t, data C.gpointer)
 	// the flush and mark_dirty calls are required; see the cairo docs and https://git.gnome.org/browse/gtk+/tree/gdk/gdkcairo.c#n232 (thanks desrt in irc.gimp.net/#gtk+)
 	C.cairo_surface_flush(surface)
 	toARGB(i, uintptr(unsafe.Pointer(C.cairo_image_surface_get_data(surface))),
-		int(C.cairo_image_surface_get_stride(surface)))
+		int(C.cairo_image_surface_get_stride(surface)), false)		// not NRGBA
 	C.cairo_surface_mark_dirty(surface)
 	C.cairo_set_source_surface(cr,
 		surface,

redo/area_windows.c

@@ -101,7 +101,7 @@ static void paintArea(HWND hwnd, void *data)
 	// first, we need to load the bitmap memory, because Windows makes it for us
 	// the pixels are arranged in RGBA order, but GDI requires BGRA
 	// this turns out to be just ARGB in little endian; let's convert into this memory
-	dotoARGB(i, (void *) ppvBits);
+	dotoARGB(i, (void *) ppvBits, FALSE);		// FALSE = not NRGBA
 
 	// the second thing is... make a device context for the bitmap :|
 	// Ninjifox just makes another compatible DC; we'll do the same

redo/area_windows.go

@@ -118,10 +118,11 @@ func doPaint(xrect *C.RECT, hscroll C.int, vscroll C.int, data unsafe.Pointer, d
 }
 
 //export dotoARGB
-func dotoARGB(img unsafe.Pointer, ppvBits unsafe.Pointer) {
+func dotoARGB(img unsafe.Pointer, ppvBits unsafe.Pointer, toNRGBA C.BOOL) {
 	i := (*image.RGBA)(unsafe.Pointer(img))
+	t := toNRGBA != C.FALSE
 	// the bitmap Windows gives us has a stride == width
-	toARGB(i, uintptr(ppvBits), i.Rect.Dx() * 4)
+	toARGB(i, uintptr(ppvBits), i.Rect.Dx() * 4, t)
 }
 
 //export areaWidthLONG

redo/imagelist_unix.go

@@ -37,7 +37,7 @@ func (i *imagelist) Append(img *image.RGBA) {
 	}
 	C.cairo_surface_flush(surface)
 	toARGB(img, uintptr(unsafe.Pointer(C.cairo_image_surface_get_data(surface))),
-		int(C.cairo_image_surface_get_stride(surface)))
+		int(C.cairo_image_surface_get_stride(surface)), false)		// not NRGBA
 	C.cairo_surface_mark_dirty(surface)
 	basepixbuf := C.gdk_pixbuf_get_from_surface(surface, 0, 0, C.gint(img.Rect.Dx()), C.gint(img.Rect.Dy()))
 	if basepixbuf == nil {

redo/imagelist_windows.c

@@ -22,7 +22,9 @@ HBITMAP unscaledBitmap(void *i, intptr_t dx, intptr_t dy)
 	bitmap = CreateDIBSection(NULL, &bi, DIB_RGB_COLORS, &ppvBits, 0, 0);
 	if (bitmap == NULL)
 		xpanic("error creating HBITMAP for unscaled ImageList image copy", GetLastError());
-	dotoARGB(i, (void *) ppvBits);
+	// image lists use non-premultiplied RGBA - see http://stackoverflow.com/a/25578789/3408572
+	// the TRUE here does the conversion
+	dotoARGB(i, (void *) ppvBits, TRUE);
 	return bitmap;
 }