andlabs-ui/areaplan.md

type Area struct {		// implements Control
	// Paint receives requests to redraw from the window system.
	Paint		chan PaintRequest

	// Keyboard receives keyboard events.
	Key		chan KeyEvent			// not covered here

	// Mouse receives mouse events.
	Mouse	chan MouseEvent		// not covered here
}

// PaintRequest represents a request to redraw an Area.
// It is sent across Area.Paint.
type PaintRequest struct {
	// Rect is the clipping rectangle that needs redraw.
	Rect		image.Rect

	// Out is a channel on which you send the image to redraw.
	Out		chan<- *image.NRGBA
}

and an example of intended use:

func myAreaGoroutine(area *ui.Area, start <-chan bool) {
	var img *image.NRGBA

	// initialize img here
	<-start		// sent after calling Window.Open()
	area.SetSize(img.Rect.Dx(), img.Rect.Dy())	// sets the internal size; scrollbars and scrolling is handled automatically
	for {
		select {
		case req := <-area.Paint:
			req.Out <- img.SubImage(req.Rect).(*image.NRGBA)
		case e := <-area.Mouse:
			// draw on a mouse click, for instance
		}
	}
}

TODO is there a race on area.SetSize()?

TODO for all of the following: verify API call data types before moving code

Drawing and Scrolling

Windows

We create another custom window class that does WM_PAINT and handles input events thereof.

For this mockup, I'll extract the message handling into its own function and assume I can call Windows API functions and use their types and constants as normal. For WM_PAINT both wparam and lparam are unused.

func repaint(s *sysData) HRESULT {
	var xrect RECT
	var ps PAINTSTRUCT

	// TODO send TRUE if we want to erase the clip area
	if GetUpdateRect(s.hwnd, &xrect, FALSE) == 0 {
		// no update rect, so we're done
		return 0
	}
	hdc, err := BeginPaint(s.hwnd, &ps)
	if hdc == 0 {		// failure
		panic(fmt.Errorf("error beginning Area repaint: %v", err))
	}

	cliprect := image.Rect(int(xrect.Left), int(xrect.Top), int(xrect.Right), int(xrect.Bottom))
	imgret := make(chan *image.NRGBA)
	defer close(imgret)
	s.paint <- PaintRequest{
		Rect:		cliprect,
		Out:		imgret,
	}
	i := <-imgret

	// drawing code here; see below

	EndPaint(s.hwnd, &ps)
	return 0
}

We can use GDI+ (gdiplus.dll) and its flat API for drawing...

GpStatus WINGDIPAPI GdipCreateBitmapFromScan0(INT width, INT height, INT stride, PixelFormat format, BYTE* scan0, GpBitmap** bitmap);
GpStatus WINGDIPAPI GdipCreateFromHDC(HDC hdc, GpGraphics **graphics);
GpStatus WINGDIPAPI GdipDrawImageI(GpGraphics *graphics, GpImage *image, INT x, INT y);
GpStatus WINGDIPAPI GdipDeleteGraphics(GpGraphics *graphics);
GpStatus WINGDIPAPI GdipDisposeImage(GpImage *image);

(GpBitmap extends GpImage.) The only problem is the pixel format: the most appropriate one is PixelFormat32bppARGB, which is not premultiplied, but the components are in the wrong order... (specifically in BGRA order) (there is no RGBA pixel format in any bit width) (TODO GdipDisposeImage seems wrong since it bypasses ~Bitmap() and goes right for ~Image() but I don't see an explicit ~Bitmap()...)

Disregarding the RGBA issue, the draw code would be

	var bitmap, graphics uintptr

	status := GdipCreateBitmapFromScan0(
		i.Rect.Dx(),
		i.Rect.Dy(),
		i.Stride,
		PixelFormat32bppARGB,
		(*byte)(unsafe.Pointer(&i.Pix[0])),
		&bitmap)
	if status != 0 {		// failure
		panic(fmt.Errorf("error creating GDI+ bitmap to blit (GDI+ error code %d)", status))
	}
	status = GdipCreateFromHDC(hdc, &graphics)
	if status != 0 {		// failure
		panic(fmt.Errorf("error creating GDI+ graphics context to blit to (GDI+ error code %d)", status))
	}
	status = GdipDrawImageI(graphics, bitmap, cliprect.Min.X, cliprect.Min.Y)
	if status != 0 {		// failure
		panic(fmt.Errorf("error blitting GDI+ bitmap (GDI+ error code %d)", status))
	}
	status = GdipDeleteGraphics(graphics)
	if status != 0 {		// failure
		panic(fmt.Errorf("error freeing GDI+ graphics context to blit to (GDI+ error code %d)", status))
	}
	status = GdipDisposeImage(bitmap)
	if status != 0 {		// failure
		panic(fmt.Errorf("error freeing GDI+ bitmap to blit (GDI+ error code %d)", status))
	}

Upon further review, there really doesn't seem to be any way around it: we have to shuffle the image data around. We seem to be in good company: go.wde needs to do so as well. But you can't be too sure...

	realbits := make([]byte, 4 * i.Rect.Dx() * I.Rect.Dy())
	q := 0
	for y := i.Rect.Min.Y; y < i.Rect.Max.Y; y++ {
		k := i.Pix[y * i.Stride:]
		for x := i.Rect.Min.X; x < i.Rect.Max.X; x += 4 {
			realbits[q + 0] = byte(k[y + x + 2])	// B
			realbits[q + 1] = byte(k[y + x + 1])	// G
			realbits[q + 2] = byte(k[y + x + 0])	// R
			realbits[q + 3] = byte(k[y + x + 3])	// A
			q += 4
		}
	}

	var bitmap, graphics uintptr

	status := GdipCreateBitmapFromScan0(
		i.Rect.Dx(),
		i.Rect.Dy(),
		i.Rect.Dy() * 4,			// got rid of extra stride
		PixelFormat32bppARGB,
		&realbits[0],
		&bitmap)
	// rest of code

We must also initialize and shut down GDI+ in uitask:

var (
	gdiplustoken uintptr
)

	// init
	startupinfo := &GdiplusStartupInput{
		GdiplusVersion:	1,
	}
	status := GdiplusStartup(&gdiplustoken, startupinfo, nil)
	if status != 0 {		// failure
		return fmt.Errorf("error initializing GDI+ (GDI+ error code %d)", status)
	}

	// shutdown
	GdiplusShutdown(gdiplustoken)

For scrolling, the custom window class will come with scrollbars. We are reponsible for scrolling ourselves:

• we handle WM_HSCROLL and WM_VSCROLL messages, extrapolating the scroll data
  • we can use GetScrollInfo to get the current position, but the example code on MSDN adjusts it manually and then calls ScrollWindow then UpdateWindow (to accelerate redraw) and then SetScrollInfo (to update the scroll info)
• line size is 1, page size is visible dimension
• call SetScrollInfo on control resizes, passing in a SCROLLINFO which indicates the above, does not include SIF_DISABLENOSCROLL so scrollbars are auto-hidden, and does not change either thumb position (nPos and nTrackPos)
• the clipping rectangle must take scrolling into account; GetScrollInfo and add the position to the sent-out cliprect (only; still need regular cliprect for drawing) with cliprect.Add()
• we should probably cache the scroll position and window sizes so we wouldn't need to call those respective functions each WM_PAINT and WM_HSCROLL/WM_VSCROLL, respectively
  • TODO will resizing a window with built-in scrollbars/adjusting the page size set the thumb and signal repaint properly?

TODO is there a function to turn a GpStatus into a string?

TODO note http://msdn.microsoft.com/en-us/library/windows/desktop/bb775501%28v=vs.85%29.aspx#win_class for information on handling some key presses, tab switch, etc. (need to do this for the ones below too)

TODO standard scrollbars cannot be controlled by the keyboard; either we must provide an option for doing that or allow scrolling ourselves (the myAreaGoroutine would read the keyboard events and scroll manually, in the same way)

GTK+

We can use GtkDrawingArea. We hook into the draw signal; it does something equivalent to

func draw_callback(widget *C.GtkWidget, cr *C.cairo_t, data C.gpointer) C.gboolean {
	var x, y, w, h C.double

	s := (*sysData)(unsafe.Pointer(data))
	// thanks to desrt in irc.gimp.net/#gtk+
	C.cairo_clip_extents(cr, &x, &y, &w, &h)
	cliprect := image.Rect(int(x), int(y), int(w), int(h))
	imgret := make(chan *image.NRGBA)
	defer close(imgret)
	s.paint <- PaintRequest{
		Rect:		cliprect,
		Out:		imgret,
	}
	i := <-imgret
	pixbuf := C.gdk_pixbuf_new_from_data(
		(*C.guchar)(unsafe.Pointer(&i.Pix[0])),
		C.GDK_COLORSPACE_RGB,
		C.TRUE,			// has alpha channel
		8,				// bits per sample
		C.int(i.Rect.Dx()),
		C.int(i.Rect.Dy()),
		C.int(i.Stride),
		nil, nil)			// do not free data
	C.gdk_cairo_set_source_pixbuf(cr,
		pixbuf,
		C.gdouble(cliprect.Min.X),
		C.gdouble(cliprect.Min.Y))
	C.g_object_unref((C.gpointer)(unsafe.Pointer(pixbuf)))		// free pixbuf
	return C.FALSE		// TODO what does this return value mean? docs don't say
}

Example 1 on this page indicates the pixels are in RGBA order, which is good.

On alpha premultiplication:

12:27	andlabs	Hi. Is the pixel data fed to gdk-pixbuf alpha premultiplied, not alpha premultiplied, or is that settable? I need to feed it data from a source that doesn't know about the underlying rendering system. Thanks.
12:29		*** KaL_out is now known as KaL
12:29	desrt	andlabs: pixbuf is non-premultiplied
12:30	mclasen	sad that this information is not obvious in the docs
12:30	andlabs	there is no information about premultiplied in any of the GTK+ documentation, period
12:30	desrt	andlabs: we have a utility function to copy it to a cairo surface that does the multiply for you...
12:30	andlabs	(in versions compatible with ubuntu 12.04, at least)
12:31	andlabs	good to know, thanks
12:31	desrt	andlabs: i think it's because gdkpixbuf existed before premultiplication was a wide practice
12:31	desrt	so at the time nobody would have asked the question
12:31	andlabs	huh

GtkDrawingArea is not natively scrollable, so we use gtk_scrolled_window_add_with_viewport() to add it to a GtkScrolledWindow with an implicit GtkViewport that handles scrolling for us. Otherwise, it's like what we did for Listbox.

TODO "Note that GDK automatically clears the exposed area to the background color before sending the expose event" decide what to do for the other platforms

Cocoa

For this one we must create a subclass of NSView that overrides the drawing and keyboard/mouse event messages.

The drawing message is -[NSView drawRect:], which just takes the NSRect as an argument. So we already need to use bleh_darwin.m to grab the actual NSRect and convert it into something with a predictable data type before passing it back to Go. If we do this:

//export our_drawRect
func our_drawRect(self C.id, rect C.struct_xrect) {

we can call our_drawRect() from this C wrapper:

extern void our_drawRect(id, struct xrect);

void _our_drawRect(id self, SEL sel, NSRect r)
{
	struct xrect t;

	t.x = (int64_t) s.origin.x;
	t.y = (int64_t) s.origin.y;
	t.width = (int64_t) s.size.width;
	t.height = (int64_t) s.size.height;
	our_drawRect(self, t);
}

This just leaves our_drawRect itself. For this mockup, I will use "Objective-Go":

var (
	// for later
	initWithBitmapDataPlanes = sel_getUid("initWithBitmapDataPlanes:pixelsWide:pixelsHigh:bitsPerSample:samplesPerPixel:hasAlpha:isPlanar:colorSpaceName:bitmapFormat:bytesPerRow:bitsPerPixel:")
)

//export our_drawRect
func our_drawRect(self C.id, rect C.struct_xrect) {
	s := getSysData(self)
	cliprect := image.Rect(int(rect.x), int(rect.y), int(rect.width), int(rect.height))
	imgret := make(chan *image.NRGBA)
	defer close(imgret)
	s.paint <- PaintRequest{
		Rect:		cliprect,
		Out:		imgret,
	}
	i := <-imgret
	// the NSBitmapImageRep constructor requires a list of pointers
	_bitmapData := [1]*uint8{&i.Pix[0]}
	bitmapData := (**C.uchar)(unsafe.Pointer(&bitmapData))
	bitmap := [[NSBitmapImageRep alloc]
		initWithBitmapDataPlanes:bitmapData
		pixelsWide:i.Rect.Dx()
		pixelsHigh:i.Rect.Dy()
		bitsPerSample:8
		samplesPerPixel:4
		hasAlpha:YES
		isPlanar:NO
		colorSpaceName:NSCalibratedRGBColorSpace		// TODO NSDeviceRGBColorSpace?
		bitmapFormat:NSAlphaNonpremultipliedBitmapFormat		// this is where the flag for placing alpha first would go if alpha came first; the default is alpha last, which is how we're doing things (otherwise the docs say "Color planes are arranged in the standard order—for example, red before green before blue for RGB color.")
		bytesPerRow:i.Stride
		bitsPerPixel:32]
	[bitmap drawAtPoint:NSMakePoint(cliprect.Min.X, cliprect.Min.Y)]
	[bitmap release]
}

Due to the size of the NSBitmapImageRep constructor, I might just have another C function that performs the NSBitmapImageRep constructor using the image.NRGBA fields.

Finally, we need to override -[NSView isFlipped] since we want to keep (0,0) at the top-left:

//export our_isFlipped
func our_isFlipped(self C.id, sel C.SEL) C.BOOL {
	return C.BOOL(C.YES)
}

For scrolling, we simply wrap our view in a NSScrollView just as we did with Listbox; Cocoa handles all the details for us.

TODO erase clip rect?

Mouse Events

TODO scroll wheel

Windows

Back to our custom window prodcedure again. We receive:

WM_LBUTTONDBLCLK
WM_LBUTTONDOWN
WM_LBUTTONUP
WM_MBUTTONDBLCLK
WM_MBUTTONDOWN
WM_MBUTTONUP
WM_RBUTTONDBLCLK
WM_RBUTTONDOWN
WM_RBUTTONUP
WM_XBUTTONDBLCLK
WM_XBUTTONDOWN
WM_XBUTTONUP 

which specify the left, middle, right, and up to two additional mouse buttons.

Each of these returns the coordinates in the LPARAM and the modifier flags in the WPARAM:

MK_CONTROL
MK_LBUTTON
MK_MBUTTON
MK_RBUTTON
MK_SHIFT
MK_XBUTTON1
MK_XBUTTON2

where the button modifier flags allow handling simultaneous clicks. The XBUTTON messages also use WPARAM to encode which button was pressed.

In order to register double-clicks, we have to specify the CS_DBLCLKS style when calling RegisterClass. A mouse click event will always be sent before a double-click event.

That just leaves mouse moves. All mouse moves are handled with WM_MOUSEMOVE, which returns the same WPARAM and LPARAM format as above (so we use the WPARAM to see which mouse buttons were held during a move).

All of these messages expect us to return 0, except the XBUTTON messages, which expect us to return TRUE.

MSDN says to use macros to get the position and XBUTTON information:

/* for all messages */
xPos = GET_X_LPARAM(lParam);
yPos = GET_Y_LPARAM(lParam);

/* for XBUTTON messages */
fwKeys = GET_KEYSTATE_WPARAM (wParam);
fwButton = GET_XBUTTON_WPARAM (wParam);

We will need to reimplement these macros ourselves.

All messages are supported on at least Windows 2000, so we're good using them all.

There does not seem to be an equivalent to the mouse entered signal provided by GTK+ and Cocoa. There is an equivalent to mouse left (WM_MOUSELEAVE), but it requires tracking support, which has to be set up in special ways.

TODO what about Alt modifier?

GTK+

• "button-press-event" for mouse button presses; needs GDK_BUTTON_PRESS_MASK and returns GdkEventButton
• "button-release-event" for mouse button releases; needs GDK_BUTTON_RELEASE_MASK and returns GdkEventButton
• "enter-notify-event" for when the mouse enters the widget; needs GDK_ENTER_NOTIFY_MASK and returns GdkEventCrossing
• "leave-notify-event" for when the mouse leaves the widget; needs GDK_LEAVE_NOTIFY_MASK and returns GdkEventCrossing
• "motion-notify-event" for when the mouse moves while inside the widget; needs GDK_POINTER_MOTION_MASK and returns GdkEventMotion

The following events may also be of use:

GDK_BUTTON_MOTION_MASK
	receive pointer motion events while any button is pressed

GDK_BUTTON1_MOTION_MASK
	receive pointer motion events while 1 button is pressed

GDK_BUTTON2_MOTION_MASK
	receive pointer motion events while 2 button is pressed

GDK_BUTTON3_MOTION_MASK
	receive pointer motion events while 3 button is pressed 

GdkEventButton tells us:

• event type: click, double-click, triple-click, release
  • a click event is always sent before a double-click and triple-click event
    • double-click: click, release, click, double-click, release
    • triple-click: C, R, C, DC, R, C, TC, R
• x and y positions of event
• modifier keys held during event: see https://developer.gnome.org/gdk3/stable/gdk3-Windows.html#GdkModifierType
  • does not appear to have a way to differentiate left and right modifier keys?
  • TODO seems to have conflicting information about Alt and Meta
  • TODO also has mouse button info?
• button ID of event, with order 1 - left, 2 - middle, 3 - right

GdkEventCrossing tells us

• whether this was an enter or a leave
• x and y positions of event
• "crossing mode" and "notification type" [not sure if I'll need these - https://developer.gnome.org/gdk3/stable/gdk3-Event-Structures.html#GdkEventCrossing]
• modifier flags (see above)
  • I think the mouse buttons are used this time but what about the event flags above

GdkEventMotion tells us

• the type of the event (I assume this is always going to be GDK_MOTION_NOTIFY)
• x and y positions of the event
• modifier keys (as above) AND POINTER BUTTONS THIS TIME

Cocoa

Our NSView subclass will override the following:

mouseDown:
mouseDragged:
mouseUp:
mouseMoved:
mouseEntered:
mouseExited:
rightMouseDragged:
rightMouseUp:
otherMouseDown:
otherMouseDragged:
otherMouseUp:

The mouse... selectors are for the left mouse button. Each of these selectors is of the form

- (void)selectorName:(NSEvent *)e

where NSEvent is a concrete type, not an abstract class, that contains all the information we need.

...almost. NSEvent doesn't record mouse position directly, but rather relative to the view's parent window. The NSView Programming Guide says we can do

	nspoint := [self convertPoint:[e locationInWindow] fromView:nil]

to get the point we want. This should also obey isFlipped:, as that affects "the coordinate system of the receiver".

For the button number, there's -[e buttonNumber]. Alas, the exact number is not documented in the reference, and neither the Event nor the NSView Programming Guides say anything. Once we do get it though, the reference also says "This method is intended for use with the NSOtherMouseDown, NSOtherMouseUp, and NSOtherMouseDragged events, but will return values for NSLeftMouse... and NSRightMouse... events also.", so since we build our class at runtime, we can just assign the same implementation function to each type of event (the sel argument will differ, but since we can just get the button number directly we don't have to worry). Of course, if the exact number isn't documented, we can't... TODO

The click count is specified in -[e clickCount], so we can distinguish between single-click and double-click easily. Note "Returns 0 for a mouse-up event if a time threshold has passed since the corresponding mouse-down event. This is because if this time threshold passes before the mouse button is released, it is no longer considered a mouse click, but a mouse-down event followed by a mouse-up event.". The Event Programing Guide says "Find out how many mouse clicks occurred in quick succession (clickCount); multiple mouse clicks are conceptually treated as a single mouse-down event within a narrow time threshold (although they arrive in a series of mouseDown: messages). As with modifier keys, a double- or triple-click can change the significance of a mouse event for an application. (See Listing 4-3 for an example.)" which indicates that a click event is sent before a double-click.

-[e modifierFlags] gives us the modifier flags. The flag reference is https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSEvent_Class/Reference/Reference.html#//apple_ref/doc/uid/20000016-SW14 - no info on left/right keys seems to be provided.

TODO do we need to override acceptsFirstMouse: to return YES so a click event is sent when changing the current program to this one?

Consensus

// MouseEvent contains all the information for a mous event sent by Area.Mouse.
// Mouse button IDs start at 1, with 1 being the left mouse button, 2 being the middle mouse button, and 3 being the right mouse button.
// (TODO If additional buttons are supported, will they be returned with 4 being the first additional button (XBUTTON1 on Windows), 5 being the second (XBUTTON2 on Windows), and so on?) (TODO get the user-facing name for XBUTTON1/2)
type MouseEvent struct {
	// Pos is the position of the mouse relative to the top-left of the area.
	Pos			image.Point

	// If the event was generated by a mouse button being pressed, Down contains the ID of that button.
	// Otherwise, Down contains 0.
	Down		uint

	// If the event was generated by a mouse button being released, Up contains the ID of that button.
	// Otherwise, Up contains 0.
	Up			uint

	// If Down is nonzero, Count indicates the number of clicks: 1 for single-click, 2 for double-click.
	// If Count > 1, at least one (TODO exactly one?) Count-1 event will be sent before a Count event.
	Count		uint

	// Modifiers is a bit mask indicating the modifier keys being held during the event.
	Modifiers		Modifiers

	// Held is a slice of button IDs that indicate which mouse buttons are being held during the event.
	// (TODO Is thisonly guarnateed to be valid if both Down and Up are zero (which indicates a mouse move)?))
	Held			[]uint
}

// HeldBits returns Held as a bit mask.
// Bit 0 maps to button 1, bit 1 maps to button 2, etc.
func (e MousEvent) HeldBits() (h uintptr) {
	for _, x := range e.Held {
		h |= uintptr(1) << (x - 1)
	}
	return h
}

// Modifiers indicates modifier keys being held during a mouse event.
// There is no way to differentiate between left and right modifier keys.
type Modifiers int
const (
	Ctrl Modifiers = 1 << iota		// the canonical Ctrl keys (Command on Mac OS X, Control on others)
	Alt						// the canonical Alt keys (Option on Mac OS X, Meta on Unix systems, Alt on others)
	Shift						// the Shift keys
)