advanced_image_usage.md

Advanced Image Usage

In rare cases when the ordinary image scaling functionality is insufficient, a couple of extra optional image attributes can be set to offer extra image cell space and scaling functionality when combined with the image dimension attributes width and height, but in most cases their default values below are sufficient:

• scale: <str> (how an image will use the available cell space) is default false if no dimension is set, or true if only one dimension is set, or both if both dimensions are set.
• fixedsize: <bool> (scale to fixed size or expand to minimum size) is default false when no dimension is set or if a scale value is set, and true otherwise.
• When fixedsize is true and only one dimension is set, then the other dimension is calculated using the image aspect ratio. If reading the aspect ratio fails, then 1:1 ratio is assumed.

See explanations of all supported values for these attributes in subsections below.

The effect of fixedsize boolean values

• When false, any width or height values are minimum values used to expand the image cell size for more available space, but cell contents or other size demands in the table might expand this cell even more than specified by width or height.
• When true, both width and height values are required by Graphwiz and specify the fixed size of the image cell, distorting any image inside if it don't fit. Any borders are normally drawn around the fixed size, and therefore, WireViz enclose the image cell in an extra table without borders when fixedsize is true to keep the borders around the outer non-fixed cell.

The effect of scale string values:

• When false, the image is not scaled.
• When true, the image is scaled proportionally to fit within the available image cell space.
• When width, the image width is expanded (height is normally unchanged) to fill the available image cell space width.
• When height, the image height is expanded (width is normally unchanged) to fill the available image cell space height.
• When both, both image width and height are expanded independently to fill the available image cell space.

In all cases (except true) the image might get distorted when a specified fixed image cell size limits the available space to less than what an unscaled image needs.

In the WireViz diagrams there are no other space demanding cells in the same row, and hence, there are never extra available image cell space height unless a greater image cell height also is set.

Usage examples

All examples of image attribute combinations below also require the mandatory src attribute to be set.

• Expand the image proportionally to fit within a minimum height and the node width:

  height: 100      # Expand image cell to this minimum height
  fixedsize: false # Avoid scaling to a fixed size
  # scale default value is true in this case

• Increase the space around the image by expanding the image cell space (width and/or height) to a larger value without scaling the image:

  width:  200  # Expand image cell to this minimum width
  height: 100  # Expand image cell to this minimum height
  scale: false # Avoid scaling the image
  # fixedsize default value is false in this case

• Stretch the image width to fill the available space in the node:

  scale: width # Expand image width to fill the available image cell space
  # fixedsize default value is false in this case

• Stretch the image height to a minimum value:

  height: 100   # Expand image cell to this minimum height
  scale: height # Expand image height to fill the available image cell space
  # fixedsize default value is false in this case

How Graphviz support this image scaling

The connector and cable nodes are rendered using a HTML <table> containing an image cell <td> with width, height, and fixedsize attributes containing an image <img> with src and scale attributes. See also the Graphviz doc, but note that WireViz uses default values as described above.