Implemented Area painting on Windows.

area_windows.go

@@ -7,6 +7,7 @@ import (
 	"syscall"
 	"unsafe"
 	"sync"
+	"image"
 )
 
 const (
@@ -23,9 +24,126 @@ var (
 	areaWndClassNumLock sync.Mutex
 )
 
+var (
+	_getUpdateRect = user32.NewProc("GetUpdateRect")
+	_beginPaint = user32.NewProc("BeginPaint")
+	_endPaint = user32.NewProc("EndPaint")
+	_gdipCreateBitmapFromScan0 = gdiplus.NewProc("GdipCreateBitmapFromScan0")
+	_gdipCreateFromHDC = gdiplus.NewProc("GdipCreateFromHDC")
+	_gdipDrawImageI = gdiplus.NewProc("GdipDrawImageI")
+	_gdipDeleteGraphics = gdiplus.NewProc("GdipDeleteGraphics")
+	_gdipDisposeImage = gdiplus.NewProc("GdipDisposeImage")
+)
+
+const (
+	// from winuser.h
+	_WM_PAINT = 0x000F
+)
+
+func paintArea(s *sysData) {
+	const (
+		// from gdipluspixelformats.h
+		_PixelFormatGDI = 0x00020000
+		_PixelFormatAlpha = 0x00040000
+		_PixelFormatCanonical = 0x00200000
+		_PixelFormat32bppARGB = (10 | (32 << 8) | _PixelFormatAlpha | _PixelFormatGDI | _PixelFormatCanonical)
+	)
+
+	var xrect _RECT
+	var ps _PAINTSTRUCT
+
+	// TODO send _TRUE if we want to erase the clip area
+	r1, _, _ := _getUpdateRect.Call(
+		uintptr(s.hwnd),
+		uintptr(unsafe.Pointer(&xrect)),
+		uintptr(_FALSE))
+	if r1 == 0 {			// no update rect; do nothing
+		return
+	}
+
+	cliprect := image.Rect(int(xrect.Left), int(xrect.Top), int(xrect.Right), int(xrect.Bottom))
+	// TODO offset cliprect by scroll position
+	// make sure the cliprect doesn't fall outside the size of the Area
+	cliprect = cliprect.Intersect(image.Rect(0, 0, 320, 240))	// TODO change when adding resizing
+	if cliprect.Empty() {		// still no update rect
+		return
+	}
+
+	r1, _, err := _beginPaint.Call(
+		uintptr(s.hwnd),
+		uintptr(unsafe.Pointer(&ps)))
+	if r1 == 0 {		// failure
+		panic(fmt.Errorf("error beginning Area repaint: %v", err))
+	}
+	hdc := _HANDLE(r1)
+
+	i := s.handler.Paint(cliprect)
+	// the pixels are arranged in RGBA order, but GDI+ requires BGRA
+	// we don't have a choice but to convert it ourselves
+	// TODO make realbits a part of sysData to conserve memory
+	realbits := make([]byte, 4 * i.Rect.Dx() * i.Rect.Dy())
+	p := 0
+	q := 0
+	for y := i.Rect.Min.Y; y < i.Rect.Max.Y; y++ {
+		nextp := p + i.Stride
+		for x := i.Rect.Min.X; x < i.Rect.Max.X; x++ {
+			realbits[q + 0] = byte(i.Pix[p + 2])		// B
+			realbits[q + 1] = byte(i.Pix[p + 1])		// G
+			realbits[q + 2] = byte(i.Pix[p + 0])		// R
+			realbits[q + 3] = byte(i.Pix[p + 3])		// A
+			p += 4
+			q += 4
+		}
+		p = nextp
+	}
+
+	var bitmap, graphics uintptr
+
+	r1, _, err = _gdipCreateBitmapFromScan0.Call(
+		uintptr(i.Rect.Dx()),
+		uintptr(i.Rect.Dy()),
+		uintptr(i.Rect.Dx() * 4),			// got rid of extra stride
+		uintptr(_PixelFormat32bppARGB),
+		uintptr(unsafe.Pointer(&realbits[0])),
+		uintptr(unsafe.Pointer(&bitmap)))
+	if r1 != 0 {			// failure
+		panic(fmt.Errorf("error creating GDI+ bitmap to blit (GDI+ error code %d; Windows last error %v)", r1, err))
+	}
+	r1, _, err = _gdipCreateFromHDC.Call(
+		uintptr(hdc),
+		uintptr(unsafe.Pointer(&graphics)))
+	if r1 != 0 {			// failure
+		panic(fmt.Errorf("error creating GDI+ graphics context to blit to (GDI+ error code %d; Windows last error %v)", r1, err))
+	}
+	r1, _, err = _gdipDrawImageI.Call(
+		graphics,
+		bitmap,
+		uintptr(xrect.Left),			// cliprect is adjusted; use original
+		uintptr(xrect.Top))
+	if r1 != 0 {			// failure
+		panic(fmt.Errorf("error blitting GDI+ bitmap (GDI+ error code %d; Windows last error %v)", r1, err))
+	}
+	r1, _, err = _gdipDeleteGraphics.Call(graphics)
+	if r1 != 0 {			// failure
+		panic(fmt.Errorf("error freeing GDI+ graphics context to blit to (GDI+ error code %d; Windows last error %v)", r1, err))
+	}
+	r1, _, err = _gdipDisposeImage.Call(bitmap)
+	if r1 != 0 {			// failure
+		panic(fmt.Errorf("error freeing GDI+ bitmap to blit (GDI+ error code %d; Windows last error %v)", r1, err))
+	}
+
+	// return value always nonzero according to MSDN
+	_endPaint.Call(
+		uintptr(s.hwnd),
+		uintptr(unsafe.Pointer(&ps)))
+}
+
 func areaWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
 	return func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
 		switch uMsg {
+		case _WM_PAINT:
+			paintArea(s)
+			return _LRESULT(0)
 		default:
 			r1, _, _ := defWindowProc.Call(
 				uintptr(hwnd),
@@ -72,3 +190,12 @@ func registerAreaWndClass(s *sysData) (newClassName string, err error) {
 	}
 	return newClassName, nil
 }
+
+type _PAINTSTRUCT struct {
+	hdc			_HANDLE
+	fErase		int32		// originally BOOL
+	rcPaint		_RECT
+	fRestore		int32		// originally BOOL
+	fIncUpdate	int32		// originally BOOL
+	rgbReserved	[32]byte
+}