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<meta name="Description" content="KLayout layout viewer and editor project page" /> |
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<meta name="Keywords" content="KLayout OASIS GDS2 viewer editor layout semiconductor mask chip design" /> |
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<meta name="abstract" content="KLayout is a free layout viewer and editor for several formats commonly used in the semiconductor industry to transfer layout data" /> |
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<meta name="URL" content="https://www.klayout.de/" /> |
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<meta name="Author" content="Matthias Koefferlein" /> |
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<title>KLayout Layout Viewer And Editor</title> |
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</div> |
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<div class="container"> |
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<h1>DXF Format</h1> |
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<p> |
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This is a brief description of the DXF format or more precisely: the subset of DXF that KLayout understands. |
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Syntactically, DXF is a very simple format. The basic problem when reading DXF however is how to interpret it. |
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Apparently, it is more or less a dump of the object properties of the CAD tool, and many questions regarding the |
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interpretation of the properties are left open. |
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</p> |
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<p> |
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The implementation of KLayout is based on a number of test cases and comparison with other viewers. |
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In some cases, the interpretation of features was varying (for example, the interpretation of array instances). |
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In that case, TrueView (see link below) was believed to be the main authority in DXF interpretation. |
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</p> |
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<p> |
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Here are some links and references to other free viewers: |
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</p> |
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<ul> |
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<li><a href="http://en.wikipedia.org/wiki/AutoCAD_DXF">DXF page on Wikipedia</a></li> |
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<li><a href="http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=12272454&linkID=10809853">DXF specification page</a></li> |
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<li><a href="http://usa.autodesk.com/adsk/servlet/pc/index?id=6703438&siteID=123112">TrueView viewer</a></li> |
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<li><a href="http://www.sharecad.org">Online viewer (www.ShareCAD.org)</a></li> |
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<li><a href="http://www.edrawingsviewer.com">eDrawings viewer</a></li> |
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</ul> |
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<h2>Basic format</h2> |
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<p> |
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DXF consists of records of a very simple structure: |
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</p> |
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<pre> |
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<Group-Code> <Value> |
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</pre> |
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<p> |
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The group code is an integer which implicitly defines the value type and |
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acts as a key for the value. |
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In ASCII DXF, group codes and values are written in a single line each. |
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These are the group codes and values relevant for layout data: |
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</p> |
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<ul> |
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<li><b>0</b>: string (keyword)</li> |
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<li><b>2</b>: string (arbitrary)</li> |
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<li><b>6</b>: string</li> |
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<li><b>8</b>: string</li> |
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<li><b>10..13</b>: double precision coordinate</li> |
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<li><b>20..23</b>: double precision coordinate</li> |
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<li><b>30..33</b>: double precision coordinate</li> |
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<li><b>39</b>: double precision coordinate</li> |
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<li><b>40..45</b>: double precision floating point value</li> |
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<li><b>50</b>: double precision angle (in degree)</li> |
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<li><b>62</b>: 16 bit integer value</li> |
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<li><b>66</b>: 16 bit integer value </li> |
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<li><b>70</b>: 16 bit integer value</li> |
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<li><b>210</b>: double precision coordinate</li> |
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<li><b>220</b>: double precision coordinate</li> |
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<li><b>230</b>: double precision coordinate</li> |
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</ul> |
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<p> |
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Pure ASCII DXF allows the lines to contain leading or trailing blanks. KLayout also tries to identify |
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stray blank lines and skip them. Some systems generate such files. |
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</p> |
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<p> |
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There is also a binary version of the DXF format with this basic structure: |
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</p> |
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<ul> |
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<li>Header (22 Bytes): "AutoCAD Binary DXF<CR><LF><SUB><NULL></li> |
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<li>16 bit integers: 2 btyes, LSB firs</li> |
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<li>double: 8 bytes, LSB firs</li> |
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<li>string: zero-terminated</li> |
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</ul> |
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<p> |
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Apparently the binary format is rarely used. It suffers from a pretty basic issue: since the data type |
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of a value - hence the byte count - is implicitly determined by the group code, exact knowledge of the data type |
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associated with each group code is required. |
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</p> |
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<h2>General structure</h2> |
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<p> |
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This is the general structure of a DXF file as KLayout understands it. This is a schematic representation. |
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The "//" comments are not part of the file - they are provided for readability. |
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In addition, group codes and values have been written on one line. In ASCII DXF, group codes and values are on separate lines. |
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The indentation indicates coherent sections. "..." indicates that other group code / value pairs may be present which are read over: |
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</p> |
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<pre> |
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// header section |
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0 "SECTION" |
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2 "HEADER" |
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... |
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0 "ENDSEC" |
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... |
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// tables section |
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0 "SECTION" |
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2 "TABLES" |
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... |
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// layer table |
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0 "TABLE" |
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2 "LAYER" |
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70 (# of layers - do not use for reading) |
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... |
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// each layer |
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0 "LAYER" |
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2 (layer name) |
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62 (color code) |
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6 (line style) |
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... |
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0 "ENDTAB" |
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... |
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0 "ENDSEC" |
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... |
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// blocks section |
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0 "SECTION" |
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2 "BLOCKS" |
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... |
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// each block |
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0 "BLOCK" |
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8 (layer name - always 0?) |
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2 (block name) |
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70 (flags - always 64?) |
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10 (base point X) |
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20 (base point Y) |
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... |
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// each entity |
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0 (entity type) |
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... (specific for entity) |
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... |
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0 "ENDBLK" |
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... |
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0 "ENDSEC" |
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... |
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// entities (top level cell) |
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0 "SECTION" |
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2 "ENTITIES" |
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... |
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// each entity |
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0 (entity type) |
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... (specific for entity) |
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... |
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0 "ENDSEC" |
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... |
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// end of file |
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0 "EOF" |
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</pre> |
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<p>KLayout reads these entities which are described in detail below:</p> |
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<ul> |
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<li><b>POLYLINE</b>: polygon, paths</li> |
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<li><b>LWPOLYLINE</b>: polygon, paths</li> |
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<li><b>SPLINE</b>: a spline line segment</li> |
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<li><b>TRACE</b>: a four-point polygon</li> |
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<li><b>ARC</b>: an arc segment</li> |
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<li><b>ELLIPSE</b>: an elliptic segment</li> |
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<li><b>INSERT</b>: cell reference</li> |
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<li><b>LINE</b>: parts of polygon contours, path</li> |
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<li><b>SOLID</b>: triangle or tetragon</li> |
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<li><b>HATCH</b>: a filled area (polygon)</li> |
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<li><b>CIRCLE</b>: a circle</li> |
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<li><b>DIMENSION</b>: a dimension drawing</li> |
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<li><b>TEXT</b>: text</li> |
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<li><b>ATTRIB</b>: text</li> |
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<li><b>MTEXT</b>: multi-line text</li> |
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</ul> |
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<h3>POLYLINE entity</h3> |
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<pre> |
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0 "POLYLINE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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70 (flags - bit 0 for closed (1) or open (0) polyline) |
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40 (start width) |
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41 (end width) |
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... |
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// each vertex |
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0 "VERTEX" |
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8 (layer name - what for?) |
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10 (position X) |
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20 (position Y) |
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42 (bulge) |
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40 (start width) |
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41 (end width) |
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... |
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0 "SEQEND" |
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</pre> |
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<p> |
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A closed polyline with a width of 0 usually creates a polygon (unless in "keep lines" mode - see below). |
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A polyline with a width > 0 creates a path. |
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A non-closed polyline with a width of 0 creates a path with width 0 or contributes to the edges that |
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will be merged in "merge lines" mode. |
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</p> |
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<p> |
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Polylines with constant width are translated into GDS PATH objects. Polylines with non-constant |
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width are translated into polygons. |
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</p> |
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<p> |
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For paths: no round ends are provided. Variable extensions have to be emulated by extending the first and last segment. |
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</p> |
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<h3>LWPOLYLINE entity for polygons</h3> |
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<pre> |
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0 "LWPOLYLINE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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70 (flags - see POLYLINE) |
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42 (bulge) |
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43 (common width) |
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... |
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// each vertex |
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10 (position X) |
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20 (position Y) |
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40 (start width of segment) |
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41 (end width of segment) |
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... |
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0 "SEQEND" |
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</pre> |
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<p> |
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LWPOLYLINE entities are alternative representations of POLYLINE entities and are treated alike. |
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</p> |
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<h3>ARC entity</h3> |
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<pre> |
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0 "ARC" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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10 (center X) |
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20 (center Y) |
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50 (start angle) |
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51 (end angle) |
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... |
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</pre> |
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<p> |
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An ARC creates a path with width 0 or contributes to the edges that |
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will be merged in "merge lines" mode. |
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The arc will be interpolated according to the number of points per circle specified |
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in the reader options. |
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</p> |
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<h3>ELLIPSE entity</h3> |
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<pre> |
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0 "ELLIPSE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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10 (center X) |
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20 (center Y) |
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11 (main axis X) |
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21 (main axis Y) |
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40 (minor axis radius) |
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41 (start angle) |
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42 (end angle) |
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... |
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</pre> |
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<p> |
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An ELLIPSE creates a path with width 0 or contributes to the edges that |
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will be merged in "merge lines" mode. |
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The arc will be interpolated according to the number of points per circle specified |
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in the reader options. |
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</p> |
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<h3>SPLINE entity</h3> |
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<pre> |
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0 "SPLINE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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71 (degree) |
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... |
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// each vertex |
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10 (position X) |
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20 (position Y) |
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... |
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// each knot |
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40 (knot value) |
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... |
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</pre> |
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<p> |
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A spline creates a path with width 0 or contributes to the edges that |
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will be merged in "merge lines" mode. |
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</p> |
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<h3>TRACE entity</h3> |
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<pre> |
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0 "TRACE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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2 (block name) |
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10 (position1 X) |
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20 (position1 Y) |
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11 (position2 X) |
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21 (position2 Y) |
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12 (position3 X) |
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22 (position3 Y) |
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13 (position4 X) |
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23 (position4 Y) |
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... |
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</pre> |
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<p> |
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A TRACE entity generates a polygon with four vertices. |
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</p> |
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<h3>SOLID entity</h3> |
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<pre> |
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0 "SOLID" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
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2 (block name) |
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10 (position1 X) |
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20 (position1 Y) |
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11 (position2 X) |
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21 (position2 Y) |
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12 (position3 X) |
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22 (position3 Y) |
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13 (position4 X) |
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23 (position4 Y) |
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... |
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</pre> |
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<p> |
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To get a correctly ordered tetragon, points 3 and 4 must be swapped. A triangle is formed by setting position 3 and 4 to the same coordinates. |
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</p> |
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<h3>DIMENSION entity</h3> |
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<pre> |
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0 "DIMENSION" |
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2 (block name) |
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8 (layer) |
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... |
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</pre> |
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<p> |
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A DIMENSION entity is only implemented as importing the drawing block without a displacement |
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using the given layer on "0" wildcard layers inside the block. |
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</p> |
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<h3>INSERT entity</h3> |
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<pre> |
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0 "INSERT" |
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8 (layer name) |
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2 (block name) |
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10 (position X) |
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20 (position Y) |
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41 (scale factor X - can be negative for mirroring) |
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42 (scale factor Y - can be negative for mirroring) |
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50 (rotation angle) |
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70 (number of columns - optional) |
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71 (number of rows - optional) |
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44 (column spacing - optional) |
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45 (row spacing - optional) |
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... |
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</pre> |
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<p> |
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The layer specified overrides the "0" layer inside the block. This requires layer specific variants. |
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This override is inherited by child cells as well. |
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</p> |
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<p> |
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The array vectors specified by number of column spacing and row spacing is rotated by the given angle, but not scaled or mirrored. |
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</p> |
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<h3>LINE entity</h3> |
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<pre> |
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0 "LINE" |
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8 (layer name) |
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210 (extrusion direction x) |
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220 (extrusion direction y) |
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230 (extrusion direction z) |
|
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10 (start position X) |
|
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20 (start position Y) |
|
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11 (start position X) |
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21 (start position Y) |
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41 (scale factor X - can be -1 for mirroring) |
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42 (scale factor Y - can be -1 for mirroring) |
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39 (thickness - can be 0) |
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... |
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</pre> |
|
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|
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<p> |
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Lines are converted into paths with the specified width or contribute to the lines merged in "merge lines" mode. |
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</p> |
|
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|
|
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<h3>CIRCLE entity</h3> |
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<pre> |
|
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0 "CIRCLE" |
|
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8 (layer name) |
|
|
210 (extrusion direction x) |
|
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220 (extrusion direction y) |
|
|
230 (extrusion direction z) |
|
|
10 (center position X) |
|
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20 (center position Y) |
|
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40 (radius) |
|
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... |
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</pre> |
|
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|
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<p> |
|
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Circles are converted to single-point, round-ended paths. |
|
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</p> |
|
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|
|
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<h3>TEXT entity</h3> |
|
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<pre> |
|
|
0 "TEXT" |
|
|
8 (layer name) |
|
|
210 (extrusion direction x) |
|
|
220 (extrusion direction y) |
|
|
230 (extrusion direction z) |
|
|
10 (position X) |
|
|
20 (position Y) |
|
|
11 (second alignment position X) |
|
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21 (second alignment position Y) |
|
|
40 (height) |
|
|
50 (rotation) |
|
|
71 (mirror flags) |
|
|
72 (horizontal alignment) |
|
|
73 (vertical alignment) |
|
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1 (text string) |
|
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</pre> |
|
|
|
|
|
<h3>MTEXT entity</h3> |
|
|
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|
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<pre> |
|
|
0 "MTEXT" |
|
|
8 (layer name) |
|
|
210 (extrusion direction x) |
|
|
220 (extrusion direction y) |
|
|
230 (extrusion direction z) |
|
|
10 (position X) |
|
|
20 (position Y) |
|
|
11 (baseline vector X) |
|
|
21 (baseline vector Y) |
|
|
40 (height) |
|
|
41 (width) |
|
|
46 (alternative width) |
|
|
50 (rotation) |
|
|
71 (alignment flags) |
|
|
75 (columns flag) |
|
|
1 (text string) |
|
|
3 (text string continuation) |
|
|
</pre> |
|
|
|
|
|
<h3>ATTRIB entity</h3> |
|
|
|
|
|
<p> |
|
|
The ATTRIB entity is basically handled like the TEXT entity except |
|
|
that group 74 is used for the vertical alignment. |
|
|
</p> |
|
|
|
|
|
<h3>HATCH entity</h3> |
|
|
|
|
|
<pre> |
|
|
0 "HATCH" |
|
|
8 (layer name) |
|
|
210 (extrusion direction x) |
|
|
220 (extrusion direction y) |
|
|
230 (extrusion direction z) |
|
|
91 (number of loops (contours)) |
|
|
// each loop: |
|
|
92 (flags, usually 3: External (bit 0) | Polyline (bit 1)) |
|
|
93 (number of edges in the first loop) |
|
|
// each point: |
|
|
10 (position X) |
|
|
20 (position Y) |
|
|
... more points with 10/20 group codes |
|
|
... more loops (group codes 92, 93, 10, 20 ...) |
|
|
... |
|
|
</pre> |
|
|
|
|
|
<p> |
|
|
A hatch entity creates a polygon. Individual polygon parts are combined with the even-odd union rule: an overlapping contour |
|
|
can cancel an area of another contour even if the orientation of both is the same. |
|
|
</p> |
|
|
|
|
|
<h2>Other topics</h2> |
|
|
|
|
|
<h3><a name="polygon_modes"/>Polygon formation and LINE/POLYLINE interpretation</a></h3> |
|
|
|
|
|
<p> |
|
|
The are several ways to form polygons from DXF input, which are controlled by the LINE/POLYLINE mode setting on the |
|
|
reader options page. The following modes are provided: |
|
|
</p> |
|
|
|
|
|
<ul> |
|
|
<li>Automatic</li> |
|
|
<li>Keep lines</li> |
|
|
<li>Create polygons from closed polylines with width = 0</li> |
|
|
<li>Merge lines with width = 0 into polygons</li> |
|
|
<li>Merge lines and auto-close open contours</li> |
|
|
</ul> |
|
|
|
|
|
<p> |
|
|
"Automatic" mode will select the following modes: |
|
|
</p> |
|
|
|
|
|
<ul> |
|
|
<li>"Keep lines" if at least one SOLID or HATCH entity is present</li> |
|
|
<li>"Create polygons from closed polylines with width = 0" if at least one closed POLYLINE or LWPOLYLINE entity with width = 0 is present</li> |
|
|
<li>"Merge lines with width = 0 into polygons" otherwise.</li> |
|
|
</ul> |
|
|
|
|
|
<p> |
|
|
The modes have the following effect: |
|
|
</p> |
|
|
|
|
|
<ul> |
|
|
<li>SOLID entities always form filled tetragons or triangles.</li> |
|
|
<li>HATCH entities always form complex polygons.</li> |
|
|
<li>Closed POLYLINE or LWPOLYLINE entities with width = 0 form polygons unless "keep lines" mode is selected. In "auto-close" mode, non-closed polylines will form a closed polygon by connecting the first and last point.</li> |
|
|
<li>Multiple segments specified by either SPLINE,ARC,ELLIPSE,LINE or POLYLINE/LWPOLYLINE entities with width = 0 are joined and, if they form a loop, create a polygon in the "merge lines" modes. In "auto-close" mode, open contours will be closed by connecting the first and last point. |
|
|
Reverse-oriented loops can create holes in outer loops.</li> |
|
|
</ul> |
|
|
|
|
|
<h3>Extrusion direction</h3> |
|
|
|
|
|
<p> |
|
|
The extrusion direction specified by the group codes 210, 220 and 230 is by default (0,0,1). This is the normal case. Extrusion direction (0,0,-1) |
|
|
is also supported. In this case, the shapes will be mirrored at the Y axis. |
|
|
</p> |
|
|
|
|
|
<h3>INSERT entities with layer specification</h3> |
|
|
|
|
|
<p> |
|
|
Layer "0" is a "wildcard" layer and can be overridden on a per-instance |
|
|
basis by a instance specific layer. If the instance has itself "0" layer assigned, no |
|
|
override takes place (or it does not have any effect). |
|
|
</p> |
|
|
|
|
|
|
|
|
|
|
|
</div> |
|
|
</body> |
|
|
</html> |
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