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Microsoft OS/2 SDK PM 02-24-1989

Comments about FATPEL


Note:
-----

You must run "make opendlg" and include the ..\dll directory in your
libpath before attempting to make or execute this application.


Description:
------------

FatPels displays a "magnified" coordinate space with some object
rendered into it.

This program illustrates the diamond metric, which is:

    1) Round control points to the nearest integer.
    2) Draw the mathematical object onto an imaginary grid where a diamond
       surrounds each pel, the tips of which exactly touch the tips of
       similar diamonds around each surrounding pel.
    3) If the object drawn enters the diamond of a pel, turn on the pel.
    4) In the case of a tie between pels, turn on the lower one
       (in whichever dimension has the tie).

Gpi actually restricts this rule by requiring that the object
touch the cross drawn between opposing vertices of the diamond.

To see the effect of rendering different objects, click in the window
to add control points, or select a different output primitive from the
Primitive menu.  You can add points by clicking with the left button,
remove them by clicking on them with the right.  If you click on a point
and hold the button down, you can drag the point around the window, with
the mathematical and rendered curves following you.  You can insert
points into a line segment by clicking on the line.

To see the effect of rendering at different scales, resize the
pels (menu command: PelSize Set pel size and shape ...).
The dimensions of the target coordinate space are determined by how
many pels of the given size will fit in the program's window.  The
sample control points follow the corners of the target space.
Resizing the window will cause a reevaluation of how many pels will fit.

You can "touch up" a rendered object by entering "edit color" mode, by
selecting "Colors Edit pel colors".  The cursor shape changes to a
hollow diamond to let you know that mouse clicks will affect pel color
rather than control point positions.  Click on the left button to set a
pel to the foreground color (i.e. color of rendered object), or the
right button for the background (i.e. field) color.

You can see the true (subject to the resolution of your monitor)
"mathematical" object by disabling rounding of control points.
The control points must be rounded for the object to correspond to
the rendered pels, according to rule (1), but it might interest you
to see how your intended object is distorted.

Note:  I repaint the window by drawing one pel into the lower left
       corner, then calling GpiBitBlt to copy it up a column, then
       copy the column across to the right.  If the lower left corner
       is clipped, then whatever happens to be covering it will get
       copied all over the window. This "feature" is for speeding
       up the repaint.	To clean it up, bring the window to the top
       and issue a redraw command.


Program commands:
-----------------

File
    Save bitmap ...
	Allow current "fatpel" screen to be saved as a BMP format file.
	Note:  this command reads the bits that are on the screen, so
	if there's garbage in the window, it will be saved.

    About ...
	Show the credits and version number.

Display
    Rendered object
	Display the mathematical object rendered into the small bitmap,
	as fat pels.

    Mathematical object
	Display the "mathematical" object, i.e. drawn to the original
	coordinates in the window, rather than the transformed down
	coordinates in the small bitmap.

    Control points
	Display markers for the control points.

    Crosshairs
	Display the crosshairs in the center of each pel.

    Pel borders
	Draw a border (in the crosshair color) around each pel.

    Rounded control points
	Round the control points before drawing, to mimic the way
	Gpi does it.  To see whether the curve follows the
	diamond metric correctly, the mathematical object must be
	drawn with its control points rounded to the nearest pel.
	Note: Selecting control points is difficult with this option on,
	because they are not displayed at their true locations.

    Auto redraw after changes
	Automatically redraw the image after any changes.

Primitive
    None
	Don't draw anything on the grid.

    GpiPolyline
    GpiPolyFillet
    GpiPolySpline
    GpiPointArc
	Draw with the given primitive.	In the case of primitives which
	require points in groups of a given size (e.g. GpiPolySpline),
	some points may be truncated when calling GPI.

Colors
    Set colors ...
	Allows various colors used by the program to be changed.
	In RGB mode, the color values are presented in hexadecimal
	notation, since it's easier to see the different color
	components that way.  You can still type in decimal numbers.
	In RGB mode, dithering is allowed.  Note that when going
	from RGB to non-RGB (default color index table) mode, the
	values are mapped to their nearest equivalents on your
	display device.

    Edit pel colors
	Sets the mouse pointer mode to "edit color".  The pointer shape
	will change to a hollow diamond.  Click with the left button to
	change a fat pel to the rendered object's color.  Click with the
	right button to set a pel to the field color.  Select this command
	again to return to "edit control point" pointer mode.

PelSize
    Set pel size and shape ...
	Set the pel size to whatever is desired.

    Drag pel size
	Allows the pel size to be specified by dragging a rectangle on the
	window.  The rectangle must be dragged from lower left to upper
	right.	The cursor will change when a button is held down, and
	a tracking rectangle will appear.  Clicking in the window with
	this option on will cause the pel to be resized to 1 by 1.

Redraw
	Redraw the screen with the current selections.

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