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5d7ab083a3
- README: added that loops can also execute zero times - accept labels only at the beginning of a line - rectangles and lines no longer use the bounding box for drawing (caused offset problems since we now correct for the line width) - dist_rect and inside_rect no longer require their input pre-sorted - pad instances now have their own structure and no longer abuse the bounding box to know the pad coordinates - Makefile: use $(GEN) for fig2dev, to reduce chattiness - when dragging a point, the symbol is now adjusted accordingly - added moving of rects, pads, circles, and arcs - added creation of pads - moved rotate_r from gui_inst.c to coord.c - new function "theta" that combines most of the angle calculations - save_pix_buf: y < 0 clipping changed width, not height git-svn-id: http://svn.openmoko.org/trunk/eda/fped@5386 99fdad57-331a-0410-800a-d7fa5415bdb3
357 lines
9.1 KiB
Plaintext
357 lines
9.1 KiB
Plaintext
fped - Footprint editor
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=======================
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fped is an editor that allows the interactive creation of footprints of
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electronic components. Footprint definitions are stored in a text format
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that resembles a programming language.
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The language is constrained such that anything that can be expressed in
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the textual definition also has a straightforward equivalent operation
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that can be performed through the GUI.
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Motivation
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----------
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KiCad already includes a footprint ("module") editor, so why do we need
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a new one ? The issue with footprint generation for KiCad is that the
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built-in module editor is basically a drawing program that only captures
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the result of the module author's interpretation of a footprint drawing,
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but does not include the steps that led to this construction.
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Furthermore, accurate measuring of dimensions in the drawing can only be
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done manually in the module editor, which makes review difficult and
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time-consuming.
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In fped, the construction process is made explicit and each step can be
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expressed in terms of the parameters that appear in the vendor's
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drawing. Dimensions can be explicitly measured and the results can be
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included in the graphical output generated by fped.
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Directly using parameters and construction steps from the reference
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drawing reduces the risk of mistakes. Visualizing the construction
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process and verificative measurements helps efficient and accurate
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review.
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Footprint definition file format
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--------------------------------
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Footprint definitions are stored in text files. The program "fped" reads
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and (soon) writes such files, visualizes their content, and provides a
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graphical editor for them.
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The syntax is unique and draws from elements of a variety of languages
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commonly found on unix systems. One specialty is that there are no
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reserved words - the language keywords appear only at the beginning of
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a line and can thus be recognized as such without restricting their use
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for identifiers. This reduces the risk of creating incompatibilities
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with existing designs when introduction future language features.
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fped uses the C preprocessor for comments, conditional compilation,
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and - to a limited extent - also macros. Long lines can be split by
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ending them with a backslash. If multiple items need to be placed in a
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single line, e.g., in a macro, they can be separated with semicolons.
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Geometry model
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--------------
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The geometry model consists of frames, vectors, and objects. The shape of
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objects is defined by a number of points. These points are produced by
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concatenating vectors.
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E.g., to draw a line from (1mm, 1mm) to (2mm, 2mm), one would make a
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vector from the origin to (1mm, 1mm) and one either from the origin or
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from the previous vector to (2mm, 2mm), and then make a line connecting
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the two points.
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Units
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- - -
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fped can calculate in mm and mil. Units are specified by following a
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number with "mm" or "mil", separated by zero or more spaces or tabs.
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Examples:
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1mm
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2 mil
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Units can be mixed in calculations, e.g.,
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set a = 1mm+20mil
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set b = 10*1mm
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All values used as dimensions must be either mm or mil.
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Vectors
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- - - -
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Vectors can be anonymous or they can be named for future reference:
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vec <base> ( <x-expr>, <y-expr> )
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<identifier>: vec <base> ( <x-expr>, <y-expr> )
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The base can be one of the following items:
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- @ is the origin of the frame containing the vector
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- . is the end of the previous vector in this frame
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- <identifier> is the name of a previous vector in the same frame
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The following example would draw the line described in the previous
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section:
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a: vec @(1mm, 1mm)
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b: vec .(1mm, 1mm)
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line a b
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Silk screen objects
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- - - - - - - - - -
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The output of fped is a footprint definition that contains pads and silk
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screen drawings (we may add more layers in the future). These items are
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called "objects". Their geometry is defined through points obtained with
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vectors.
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A line connects two points:
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line <point-a> <point-b> [<width>]
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The points can be specified with @, ., and an identifier, just like
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a vector base. The option width specifies the thickness of the silk
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screen line. If omitted, a hard-coded default of 15 mil is used.
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A rectangle has sides parallel to the x and y axis and is defined
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by two diagonally opposite corners:
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rect <point-a> <point-b> [<width>]
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A circle is defined by its center and a point on the circle:
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circ <center> <point> [<width>]
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This example draws a unit circle:
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vec @(1mm, 0mm)
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circ @ .
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An arc is like a circle, but the part of the circle drawn is determined
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by two points. The first point determines the radius and the starting
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angle. The second point only determines the end angle but its distance
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from the center is ignored.
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arc <center> <radius> <end> [<width>]
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The arc is drawn in a counter-clockwise direction. The following example
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draws an arc of the unit circle in the x > 0, y > 0 quadrant:
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from: vec @(1mm, 0mm)
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to: vec @(0mm, 1mm)
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arc @ from to
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Pads
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- -
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Pads are similar to rectangles, but they also have a name.
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pad "<name>" <point-a> <point-b>
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Variables can be expanded in a pad's name by prefixing their name with
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a dollar sign. The ${name} syntax is also available.
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Example:
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vec @(1mm, 1mm)
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pad "1" @ .
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Measurements
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- - - - - -
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Measurements show the distance between two points:
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meas <point-a> <point-b> <offset>
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The offset is the distance from the imaginary line connecting points A
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and B the measurement line is draw:
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- if the offset is 0mm, the line will connect A and B
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- if the offset is positive, the line would be on the left-hand side when
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traveling from A to B
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- if the offset is negative , the line would be on the right-hand side when
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traveling from A to B
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Example:
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a: vec @(-1mm, 1mm)
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b: vec @(1mm, 1mm)
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meas a b 0.2 mm
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Frames
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- - -
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Frames are used to group things and to reuse them multiple times. Frames
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must be defined before they can be used:
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frame <name> {
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... items ...
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}
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Once defined, a frame is placed at a given location with
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frame <name> <point>
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The frame definitions must precede all other items in a footprint
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description. Frames cannot be defined inside other frames, but frames
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can invoke each other recursively.
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For example, this puts two unity squares, one centered at (0 mm, 0 mm),
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the other at (2 mm, 0 mm):
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frame unit_square {
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a: vec @(-0.5mm, -0.5mm)
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b: vec .(1mm, 1mm)
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rect a b
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}
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frame unit_square @
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vec @(2mm, 0mm)
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frame unit_square .
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Names and variables
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-------------------
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fped uses several name spaces:
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- frame names occupy one global name space
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- vector names occupy name spaces delimited by the frame they're
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contained in. A vector name is only visible inside the frame in which
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it is defined.
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- variable names occupy name spaces delimited by the frame they're
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contained in. A variable lookup starts in the frame in which the
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corresponding expression appears and propagates to outer frames
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until the variable is found.
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- pads occupy one global name space (this is currently not enforced)
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Note that names cannot be redefined. E.g., this does not work:
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set a = 1
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set a = a+1
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The names spaces of frames, vectors, variables, and pads are separate
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from each other.
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Simple variables
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- - - - - - - -
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A variable with a single value is defined with the following
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assignment syntax:
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set <identifier> = <expression>
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Example:
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set a = b+2
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Loops
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- - -
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A loop is a variable with a range of values:
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loop <identifier> = <from>, <to>
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The variable assumes all the values i for <from> <= i <= <to>, in
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increments of one. E.g.,
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loop n = 1, 3
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and
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loop n = 1, 3.5
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both assign the values 1, 2, and 3 to the variable "n". The
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following loop would not execute at all:
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loop n = 1, 0
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When a loop is executed, the objects contained in the body of the
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enclosing frame are generated for each value of the variable. If
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a frame contains multiple loops, all possible combinations of the
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values are generated.
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The following example draws three concentric circles around the
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origin, with radii 1, 2, and 3:
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loop x = 1, 3
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vec @(x*1mm, 0mm)
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circ @ .
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Tables
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- - -
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Tables combine values for multiple variables. Like loops, they are
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used to iteratively generate objects. A table begins with a row of
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variable names, followed by one or more rows with values. Rows are
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enclosed in curly braces and their elements are separated by commas.
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table
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{ <identifier>, ... }
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{ <expression>, ... }
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...
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Like loops, tables are iterated to generate objects. The following
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example is equivalent to the one in the previous section:
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table
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{ x }
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{ 1mm }
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{ 2mm }
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{ 3mm }
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vec @(x, 0mm)
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circ @ .
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Note that we can set the unit of the values directly in this case.
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Iteration is performed over rows. All variables of the table are set
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to the value in the respective row at the same time. For example, in
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table
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{ x, y }
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{ 1, 2 }
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{ 3, 4 }
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(x, y) assume the values (1, 2) and (3, 4).
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Expressions
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-----------
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Expressions can contain numeric constants (in non-exponential notation),
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variable names, the arithmetic operations +, -, *, /, and unary -.
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Parentheses can be used to change precedence.
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GUI
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---
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Keys:
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space reset user coordinates
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+, = zoom in (like mouse wheel forward)
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- zoom out (like mouse wheel backward)
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. cursor position to screen center (like middle click)
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* zoom and center to extents
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# zoom and center to currently active frame instance
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