Description
This property defines an object's co-ordinate system. It is a character string with one of the following values; 'Inherit', 'Prop', 'Pixel', 'RealPixel', 'ScaledPixel', 'User' or 'Cell' (graphics children of a Grid only).
If Coord is 'Inherit', the co-ordinate system for the object is inherited from its parent. Note that the default value of Coord for the system object '.' is 'Prop', so by default all objects created by ⎕WC inherit 'Prop'.
If Coord is 'Prop', the origin of the object's parent is deemed to be at its top left interior corner, and the scale along its x- and y-axes is 100. The object's position and size (Posn and Size properties) are therefore specified and reported as a percentage of the dimensions of the parent object, or, for a Form, of the screen.
If Coord is 'RealPixel', the origin of the object's parent is deemed to be at its top left interior corner, and the scale along its x- and y-axes is measured in physical pixel units. The object's position and size (Posn and Size properties) are therefore reported and set in physical pixel units. If you set Coord on the system object to 'Pixel', the value of its Size property gives you the resolution of your screen. Note that pixels are numbered from 0 to (Size -1).
If Coord is 'ScaledPixel' the number of pixels specified for Posn, Size, and other such properties will be automatically scaled by Dyalog APL according to the user's chosen display scaling factor. So if you specify an Edit object to be 80 pixels wide and 20 pixels high, and the user's scaling factor is 150%, Dyalog will automatically draw it 120 pixels wide and 30 pixels high. Dyalog will also de-scale coordinate values reported by ⎕WG and event messages.
If Coord is 'Pixel', it is interpreted as either 'RealPixel' or 'ScaledPixel' according to the value of the Dyalog_Pixel_Type parameter, which is either ScaledPixel or RealPixel. See Dyalog_Pixel_Type.
If this parameter is not specified, the default is RealPixel. So by default, when you set Coord to Pixel, it will be treated as RealPixel.
If Coord is 'User', the origin and scale of the co-ordinate system are defined by the values of the YRange and XRange properties of the parent object. Each of these is a 2-element numeric vector whose elements define the co-ordinates of top left and bottom right interior corners of the (parent) object respectively.
Note that if Coord is 'User' and you change the values of YRange and/or XRange of the parent, the object (and all its siblings with Coord 'User') are redrawn (and clipped) according to the new origin and scale defined for the parent. The values of their Posn, Size and Points properties are unaffected. Changing YRange and/or XRange therefore provides a convenient and efficient means to "pan and zoom".
The Coord property for graphic objects created as children of a Grid may also be set to Cell. Apart from being easier to compute, a graphic drawn using cell coordinates will expand and contract when the grid rows and columns are resized.
This statement creates a button 10 pixels high, 20 pixels wide, and 5 pixels down and along from the top-left corner of the parent Form T.
'T.B1'⎕WC'Button' 'OK'(5 5)(10 20)('Coord' 'Pixel')
If you set Coord to 'RealPixel' in the Root object '.', then query its Size, you get the dimensions of the screen in pixels, i.e.
'.' ⎕WS 'Coord' 'RealPixel'
'.' ⎕WG 'Size'
480 640
If you set Coord to 'ScaledPixel' in the Root object '.', then query its Size, you get the virtual resolution of the screen, i.e.
'.'⎕WS 'Coord' 'ScaledPixel'
'.'⎕WG'Size'
1080 1920