NAME
tweak – edit image files, subfont files, face files, etc.

SYNOPSIS
tweak [ file ... ]

DESCRIPTION
Tweak edits existing files holding various forms of images. To create original images, start from an existing image, subfont, etc.

Tweak reads its argument files and displays the resulting images in a vertical column. If the image is too wide to fit across the display, it is folded much like a long line of text in an rio window. Under each image is displayed one or two lines of text presenting its parameters. The first line shows the image's depth, the number of bits per pixel; r, the rectangle covered by the image; and the name of the file from which it was read. If the file is a subfont, a second line presents a hexadecimal 16–bit offset to be applied to character values from the subfont (typically as stored in a font file; see font(6)); and the subfont's n, height, and ascent as defined in cachechars(2).

By means described below, magnified views of portions of the images may be displayed. The text associated with such a view includes mag, the magnification. If the view is of a single character from a subfont, the second line of text shows the character's value (including the subfont's offset) in hexadecimal and as a character in tweak's default font; the character's x, top, bottom, left, and width as defined in cachechars(2); and iwidth, the physical width of the image in the subfont's image.

There are two methods to obtain a magnified view of a character from a subfont. The first is to click mouse button 1 over the image of the character in the subfont. The second is to select the char entry on the button 3 menu, point the resulting gunsight cursor at the desired subfont and click button 3, and then type at the text prompt at the bottom of the screen the character value, either as a multi–digit hexadecimal number or as a single rune representing the character.

To magnify a portion of other types of image files, click button 1 over the unmagnified file. The cursor will switch to a cross. Still with button 1, sweep a rectangle, as in rio, that encloses the portion of the image to be magnified. (If the file is 16x16 or smaller, tweak will just magnify the entire file; no sweeping is necessary.)

Pressing buttons 1 and 2 within magnified images changes pixel values. By default, button 1 sets the pixel to all zeros and button 2 sets the pixel to all ones.

Across the top of the screen is a textual display of global parameters. These values, as well as many of the textual values associated with the images, may be edited by clicking button 1 on the displayed value and typing a new value. The values along the top of the screen are:
mag   Default magnification.
val(hex)
The value used to modify pixels within magnified images. The value must be in hexadecimal, optionally preceded by a tilde for bitwise negation.
but1
but2
The pixel value written when the corresponding button is pressed over a pixel.
invert–on–copy
Whether the pixel values are inverted when a copy operation is performed.

Under button 3 is a menu holding a variety of functions. Many of these functions prompt for the image upon which to act by switching to a gunsight cursor; click button 3 over the selection, or click a different button to cancel the action.
openRead and display a file. The name of the file is typed to the prompt on the bottom line.
readReread a file.
write
Write a file.
copyUse the copy function, default S, to transfer a rectangle of pixels from one image to another. The program prompts with a cross cursor; sweep out a rectangle in one image or just click button 3 to select the whole image. The program will leave that rectangle in place and attach another one to the cursor. Move
that rectangle to the desired place in any image and click button 3, or another button to cancel the action.
charAs described above, open a magnified view of a character image in a subfont.
pixels
Report the coordinate and value of individual pixels indicated by pressing button 3. This is a mode of operation canceled by pressing button 1 or 2.
close
Close the specified image. If the image is the unmagnified file, also close any magnified views of that file.
exitQuit tweak. The program will complain once about modified but unwritten files.

SOURCE
/sys/src/cmd/tweak.c

SEE ALSO
cachechars(2), image(6), font(6)

BUGS
For a program written to adjust width tables in fonts, tweak has been pushed unreasonably far.
Copyright © 2017 Alcatel-Lucent. All rights reserved.