draw

type Color struct{ R, G, B, A float32 }

type Key int

type MouseButton int

type MouseClick struct {
	// X and Y are the screen position in pixels, relative to the drawing area.
	// X goes from left to right, starting at 0 and Y goes from top to bottom
	// starting at 0.
	// This means that pixel 0,0 is the top-left pixel in the drawing area (not
	// the title bar).
	X, Y   int
	Button MouseButton
}

type UpdateFunction func(window Window)

type Window interface {
	// Close closes the window which will stop the update loop after the current
	// frame (you will usually want to return from the update function after
	// calling Close or another frame will be displayed).
	Close()

	// Size returns the window's size in pixels.
	Size() (width, height int)

	// SetFullscreen toggles between the fixed-size window with title and border
	// and going full screen on the monitor that the window is placed on when
	// the call to SetFullscreen(true) occurs.
	// Use Window.Size to get the new size after this.
	// By default the window is not fullscreen. It always starts windowed.
	SetFullscreen(f bool)

	// ShowCursor set the OS' mouse cursor to visible or invisible. It defaults
	// to visible if you do not call ShowCursor.
	ShowCursor(show bool)

	// WasKeyPressed reports whether the specified key was pressed at any time
	// during the last frame. If the user presses a key and releases it in the
	// same frame, this function stores that information and will return true.
	// See the Key... constants for the available keys that can be queried.
	// NOTE do not use this for text input, use Characters instead.
	WasKeyPressed(key Key) bool

	// IsKeyDown reports whether the specified key is being held down at the
	// moment of calling this function.
	// See the Key... constants for the available keys that can be queried.
	IsKeyDown(key Key) bool

	// Characters returns all pressed keys translated to characters that
	// happened in the last frame. The runes in the string are ordered by the
	// time that the keys were entered.
	Characters() string

	// IsMouseDown reports whether the specified button is down at the time of
	// the function call
	IsMouseDown(button MouseButton) bool

	// Clicks returns all MouseClicks that occurred during the last frame.
	Clicks() []MouseClick

	// MousePositoin returns the current mouse position in pixels at the time of
	// the function call. It is relative to the drawing area of the window.
	MousePosition() (x, y int)

	// MouseWheelY returns the aggregate vertical mouse wheel rotation during
	// the last frame. A value of 1 typically corresponds to one tick of the
	// wheel. A positive value means the wheel was rotated forward, away from
	// the user, a negative value means the wheel was rotated backward towards
	// the user.
	MouseWheelY() float64

	// MouseWheelX returns the aggregate horizontal mouse wheel rotation during
	// the last frame. A value of 1 typically corresponds to one tick of the
	// wheel. A positive value means the wheel was rotated right, a negative
	// value means the wheel was rotated left.
	MouseWheelX() float64

	// DrawPoint draws a single point at the given screen position in pixels.
	DrawPoint(x, y int, color Color)

	// DrawLine draws a one pixel wide line from the first point to the second
	// (inclusive).
	DrawLine(fromX, fromY, toX, toY int, color Color)

	// DrawRect draws a one pixel wide rectangle outline.
	DrawRect(x, y, width, height int, color Color)

	// FillRect draws a filled rect.
	FillRect(x, y, width, height int, color Color)

	// DrawEllipse draws a one pixel wide ellipse. The top-left corner of the
	// surrounding rectangle is given by x and y, the horizontal and vertical
	// diameters are given by width and height.
	DrawEllipse(x, y, width, height int, color Color)

	// FillEllipse behaves like DrawEllipse but fills the ellipse with the color
	// instaed of only drawing the outline.
	FillEllipse(x, y, width, height int, color Color)

	// DrawImageFile draws the untransformed image at the give position. If the
	// image file is not found or has the wrong format an error is returned.
	DrawImageFile(path string, x, y int) error

	// DrawImageFileTo draws the image to the given screen rectangle, possibly
	// scaling it in either direction, and rotates it around the rectangles
	// center point by the given angle. The rotation is clockwise.
	// If the image file is not found or has the wrong format an error is
	// returned.
	DrawImageFileTo(path string, x, y, w, h, rotationCWDeg int) error

	// DrawImageFileRotated draws the image with its top-left corner at the
	// given coordinates but roatated clockwise about the given angle in degrees
	// around its center. This means its top-left corner will only actually be
	// at the given location if the rotation is 0.
	// If the image file is not found or has the wrong format an error is
	// returned.
	DrawImageFileRotated(path string, x, y, rotationCWDeg int) error

	// DrawImageFilePart lets you specify the source and destination rectangle
	// for the image file to be drawn. The image is rotated about its center by
	// the given angle in degrees, clockwise. You may flip the image by
	// specifying a negative width or height. E.g. to flip in x direction,
	// instead of
	//
	//     DrawImageFilePart("x.png", 0, 0, 100, 100, 0, 0, 100, 100, 0)
	//
	// you would do
	//
	//     DrawImageFilePart("x.png", 100, 0, -100, 100, 0, 0, 100, 100, 0)
	//
	// swapping the source rectangle's left and right positions.
	//
	// If the image file is not found or has the wrong format an error is
	// returned.
	DrawImageFilePart(
		path string,
		sourceX, sourceY, sourceWidth, sourceHeight int,
		destX, destY, destWidth, destHeight int,
		rotationCWDeg int,
	) error

	// GetTextSize returns the size the given text would have when being drawn.
	GetTextSize(text string) (w, h int)

	// GetScaledTextSize returns the size the given text would have when being
	// drawn at the given scale.
	GetScaledTextSize(text string, scale float32) (w, h int)

	// DrawText draws a text string. New line characters ('\n') are not drawn
	// but force a line break and the next character is drawn on the line below
	// starting again at x.
	DrawText(text string, x, y int, color Color)

	// DrawScaledText behaves as DrawText, but the text is scaled. If scale = 1
	// this behaves exactly like DrawText, scales > 1 make the text bigger,
	// scales < 1 shrink it. Scales <= 0 will draw no text at all.
	DrawScaledText(text string, x, y int, scale float32, color Color)

	// PlaySoundFile only plays WAV sounds. If the file is not found or has the
	// wrong format an error is returned.
	PlaySoundFile(path string) error
}